section name header

Introduction

VA Class:AH000

ATC Class:R06A

AHFS Class:

Associated Monographs

Antihistamines, which inhibit the effects of histamine at H1 receptors, have been classified as first generation (i.e., relatively sedating) or second generation (i.e., relatively nonsedating).

Uses

[Section Outline]

Antihistamines are most often used to provide symptomatic relief of allergic symptoms caused by histamine release. The drugs are not curative and merely provide palliative therapy. Antihistamines are used only as adjunctive therapy to epinephrine and other standard measures in the treatment of anaphylactic reactions and laryngeal edema after the acute manifestations have been controlled. Individual patients vary in their response to antihistamines. A specific antihistamine that provides dramatic relief without adverse effects to one patient may produce intolerable adverse effects in another patient. Trial of various antihistamines may be necessary to determine which drug will provide relief while causing minimal adverse effects.

Nasal Allergies and the Common Cold !!navigator!!

Antihistamines are most beneficial in the management of nasal allergies. Seasonal allergic rhinitis (e.g., hay fever) and perennial (nonseasonal) allergic rhinitis are benefited more than perennial nonallergic (vasomotor) rhinitis. Orally administered antihistamines generally provide symptomatic relief of rhinorrhea, sneezing, oronasopharyngeal irritation or itching, lacrimation, and red, irritated, or itching eyes associated with the early response to histamine.100,149,168,169,170,487,494,509 The drugs generally are not effective in relieving symptoms of nasal obstruction, which are characteristic of the late allergic reaction,100,170,487 although limited data indicate that cetirizine and levocetirizine may relieve some symptoms of late allergic reactions.581,681,682 Antihistamines (e.g., azelastine) also may be administered intranasally for the symptomatic relief of seasonal allergic rhinitis.526,527,528 (See Uses in Azelastine 52:02.) In comparative studies, intranasal azelastine was more effective than placebo and at least as effective as oral antihistamines (e.g., cetirizine, terfenadine [no longer commercially available in the US]) or intranasal corticosteroids in relieving allergic rhinitis.529,530,531,532,533,534,535,536,537,538,539 However, unlike intranasal corticosteroids, azelastine does not appear to exhibit local histologic anti-inflammatory activity;529,530 therefore, beneficial effects on nasal obstruction appear to result principally from antihistaminic and/or other activity.530,531,535

Chronic nasal congestion and headache caused by edema of the paranasal sinus mucosa are often refractory to antihistamine therapy. In the treatment of hay fever, antihistamines are more likely to be beneficial when therapy is initiated at the beginning of the hay fever season when pollen counts are low (e.g., before pollination begins) and if used regularly during the pollen season. Antihistamines are less likely to be effective when pollen counts are high, when pollen exposure is prolonged, and when nasal congestion is prominent.149,151,168

Although antihistamines frequently are used for symptomatic relief in the common cold, evidence of effectiveness remains to be clearly established.100,129,130,398,401,402,467,487,494,525,540,564,565 Antihistamines cannot prevent, cure, or shorten the course of the common cold,100,129,130,398,400,402 but may provide some symptomatic relief.130,169,390,392,400,401,519,540,564,565 Conventional (prototypical, first generation) antihistamines (e.g., those with anticholinergic activity) are considered effective in relieving rhinorrhea and sneezing associated with the common cold,130,169,390,392,400,540,564 but evidence of efficacy in relieving oronasopharyngeal itching, lacrimation, or itching eyes associated with this condition currently is lacking.169 Nonsedating (second generation) antihistamines do not appear to be effective in relieving rhinorrhea, suggesting that histamine is not a principal mediator of this manifestation.519,524,564 The extent to which histamine contributes to other manifestations of the common cold currently is unclear, but pathogenesis of the full constellation of symptoms that constitute the common cold appears to be complex, involving a number of mediators and neurologic mechanisms.519,520,521,522,523

Routine, prolonged administration of fixed combinations containing antihistamines, nasal decongestants, anticholinergics, analgesic-antipyretics, caffeine, antitussives, and/or expectorants has been questioned.100,390 Single-ingredient products generally are safer than combination products,100 while also facilitating dosage adjustment.100,390 There is no evidence that combinations containing 2 or more antihistamines are more effective than one antihistamine or that combinations of subtherapeutic doses of 2 or more antihistamines are more effective than therapeutic doses of one antihistamine.100,390,397,398 Oral antihistamine combinations containing an analgesic-antipyretic and/or nasal decongestant; an antitussive and nasal decongestant; an analgesic-antipyretic, antitussive, and nasal decongestant; or an antitussive may be rational if each ingredient has demonstrated clinical effectiveness and is present in therapeutic dosage.100,390,397,398,399 Selective use of such combinations can provide a convenient and rational approach for relief of concurrent symptoms (e.g., rhinorrhea, nasal congestion, cough), which often are present in allergic rhinitis and other conditions (e.g., common cold), by allowing the patient to use a single combination rather than multiple single-entity preparations.100,390,398,487 Combination preparations generally should be used only when symptoms amenable to each ingredient are present concurrently.100,390,398 Combinations containing an antihistamine and an expectorant, anticholinergic agent, or bronchodilator are not considered rational.100,390

Although cough and cold preparations that contain antihistamines, nasal decongestants, cough suppressants, and/or expectorants commonly were used in pediatric patients younger than 2 years of age, systematic reviews of controlled trials have concluded that nonprescription (over-the-counter, OTC) cough and cold preparations are no more effective than placebo in reducing acute cough and other symptoms of upper respiratory tract infection in these patients.693 Furthermore, adverse events, including deaths, have been (and continue to be) reported in pediatric patients younger than 2 years of age receiving these preparations.693 (See Cautions: Pediatric Precautions.)

Other Allergic Conditions !!navigator!!

Antihistamines are often effective in the treatment of allergic dermatoses and other dermatoses associated with histamine release, but effectiveness varies with the causative agent and symptoms may return when the drug is stopped. Antihistamines have been used in the symptomatic treatment of chronic idiopathic urticaria;176,177,178,179,509,567,568,569,570,571,572,573,669,670,683,684 occasionally, patients who do not experience adequate relief with an antihistamine (H1-receptor antagonist) alone may benefit from the addition of an H2-receptor antagonist.176,177,178,179 However, in one study, the addition of an H2-receptor antagonist did not provide a substantial increase in response (as determined by reduction in whealing).175 Some antihistamines also may symptomatically relieve pruritus accompanying atopic dermatitis, contact dermatitis, pruritus ani or vulvae, and insect bites. Some evidence suggests that first generation antihistamines such as hydroxyzine and diphenhydramine may be more effective than second generation antihistamines (e.g., terfenadine [no longer commercially available in the US], loratadine) for the relief of pruritus associated with certain allergic dermatoses (e.g., atopic dermatitis), but additional study is needed to elucidate further the relative efficacy of these drugs as antipruritics.487,495,496 Antihistamines also may be used in the treatment of dermatographism. Patients with dermatographism or other urticarial conditions who do not experience adequate relief with an antihistamine (H1-receptor antagonist) alone may benefit from the addition of an H2-receptor antagonist to enhance relief of pruritus and wheal formation.173,174,321,487

Antihistamines are useful in the management of allergic conjunctivitis caused by foods or inhaled allergens. Allergic or hypersensitivity reactions to penicillin, streptomycin, sulfonamides, and other drugs may be amenable to antihistamine therapy. Pruritus and urticaria accompanying these conditions usually are temporarily relieved; edema is more resistant and serum sickness is not benefited.

Symptoms of mild transfusion reactions not caused by ABO incompatibility or pyrogens may be alleviated by antihistamines. The drugs should not be added to blood being transfused. Antihistamines may be administered prophylactically to patients with a history of transfusion reactions, but the drugs should not be given routinely to patients receiving blood. Antihistamines also may be useful to prevent sequelae following desensitization procedures and allergic reactions to radiographic contrast media. It must be kept in mind that prophylactic use of antihistamines may mask incipient signs of allergic reactions, and the patient's hypersensitivity may not be recognized until a serious reaction occurs.

Although epinephrine is the initial drug of choice for patients with anaphylactic or anaphylactoid reactions, antihistamines are useful in the ancillary treatment of pruritus, urticaria, angioedema, and bronchospasm associated with these reactions.487,492,493 Concurrent use of H1- and H2-receptor antagonists appears to reduce the adverse effects of histamine on the peripheral vasculature and myocardium during anaphylaxis.487,492

Asthma !!navigator!!

Antihistamines may provide some benefit in certain asthmatic patients, but the drugs usually are not effective in treating bronchial asthma per se and should not be used in the treatment of severe acute asthma attacks. In addition, antihistamines are not included in the usual recommended regimens for the management of asthma, including long-term control of the disease.566 Antihistamine and decongestant combinations may provide symptomatic relief (e.g., of rhinitis) in patients with chronic rhinitis and persistent asthma, but the drugs have not been shown to have a protective effect on lower airways; other agents (e.g., inhaled corticosteroids) are for protective effects on lower airways.566 In general, patients with predictable seasonal asthma should receive long-term anti-inflammatory therapy (e.g., inhaled corticosteroids, mast-cell stabilizers), initiated prior to the anticipated onset of exposure to allergens and continued throughout the season.566 The drugs may be used with caution to treat hay fever or other airway disorder with a histamine-mediated component in patients with such disorders and asthma. Although some clinicians believe that the anticholinergic effects (e.g., reduction of nasal secretions) of some of these drugs may cause thickening of bronchial secretions resulting in further airway obstruction in asthmatics, especially those with status asthmaticus, most experts consider complete avoidance of currently available antihistamines in asthmatics unjustified.467,481,484,487 (See Cautions: Precautions and Contraindications.)

Motion Sickness and Vertigo !!navigator!!

Some antihistamines (e.g., dimenhydrinate, diphenhydramine, meclizine, promethazine) are useful for the prevention and treatment of nausea, vomiting, and/or vertigo associated with motion sickness328,341,342,343,344,345,346,347,348 and they are considered the drugs of choice for the management of this condition.341,342,345,346,347 For additional information on the use of antihistamines for the management of motion sickness, see Dimenhydrinate and see Meclizine Hydrochloride in 56:22.08. Dimenhydrinate and meclizine have also been used in the symptomatic treatment of vertigo associated with diseases affecting the vestibular system (e.g., labyrinthitis, Ménière's disease). Nonphenothiazine antihistamines are less effective than the phenothiazines in controlling nausea and vomiting not related to vestibular stimulation.

Nausea and Vomiting of Pregnancy !!navigator!!

Doxylamine succinate is used in fixed combination with pyridoxine hydrochloride for the management of nausea and vomiting of pregnancy in women who have not responded to conservative management.705,706 (See Uses in Doxylamine 4:04.)

Chemotherapy-induced Nausea and Vomiting !!navigator!!

Some antihistamines (e.g., diphenhydramine) may be useful as adjunctive antiemetic agents to prevent chemotherapy-induced nausea and vomiting†; however, the American Society of Clinical Oncology currently does not recommend that antihistamines be used alone as antiemetic agents in patients receiving chemotherapy.680

Insomnia !!navigator!!

Some antihistamines, especially the ethanolamines such as diphenhydramine and doxylamine, are used for their sedative effects as nighttime sleep aids.197,407,408 The US Food and Drug Administration (FDA) states that diphenhydramine currently is the only antihistamine commercially available in the US that has been shown to be both safe and effective for self-medication as a nighttime sleep aid.407 In individuals who experience occasional sleeplessness or those who have difficulty falling asleep, diphenhydramine (administered as either the citrate or hydrochloride salt) is more effective than placebo in reducing sleep onset (i.e., time to fall asleep) and increasing the depth and quality of sleep.197,407 Although the safety and efficacy of doxylamine as a nighttime sleep aid have not been fully established,197,407 the FDA states that, pending further accumulation of data, doxylamine-containing nighttime sleep aids that have been approved for this use may continue to be marketed in the US.407 Some proprietary sleep aids also may continue to contain pyrilamine despite a lack of substantial evidence of safety and efficacy for use of this antihistamine as a nighttime sleep aid;197,407 however, many such preparations have been or are likely to be reformulated with other antihistamines (e.g., diphenhydramine).407

Other Systemic Uses !!navigator!!

Some antihistamines such as diphenhydramine have been used effectively as antitussives. Diphenhydramine also may be useful in the management of tremor early in the course of parkinsonian syndrome673,674,675 and in the management of drug-induced extrapyramidal reactions.676

Topical and Other Local Uses !!navigator!!

Diphenhydramine and tripelennamine (no longer commercially available in the US; extemporaneous formulation would be necessary) are used topically for temporary relief of pruritus and pain associated with various skin conditions including minor burns, sunburn, minor cuts or scrapes, insect bites, or minor skin irritations.196,349 The drugs may provide effective localized antipruritic activity when applied topically if pruritus and discomfort are histamine mediated; the weak local anesthetic action of the drugs also may contribute to the overall effect.349 However, many clinicians suggest that topical diphenhydramine not be used on large areas of the body or more often than directed,672 since increased percutaneous absorption of the drug may occur that can result in systemic adverse effects and toxicity.556,557 (See Acute Toxicity: Manifestations.) Topical diphenhydramine also should not be used for self-medication in the management of varicella (chickenpox) or measles without first consulting a clinician.672

Some antihistamines also have been used for their topical or local anesthetic effects in ophthalmic, urologic, proctologic, gastroscopic, otolaryngologic, and dental procedures. However, topical use of antihistamines generally is discouraged because sensitivity reactions (e.g., sensitization, hypersensitivity) may result.11,44,50,149,151,345,355,356,357,358,359,368,379,380,436 (See Cautions: Sensitivity Reactions.) In addition, use of certain antihistamines (e.g., diphenhydramine) for local anesthesia via local infiltration also is discouraged because of the risk of local tissue necrosis.411,437 If the drugs are used topically as antipruritics, therapy generally should be short-term (i.e., for no longer than 7 days) because of the increasing risk of sensitivity reactions from prolonged or repeated use.349 Antihistamines are more effective, especially if pruritus is generalized, and are less likely to cause sensitivity reactions when the drugs are administered systemically rather than applied topically.349

Dosage and Administration

[Section Outline]

Administration !!navigator!!

Antihistamines usually are administered orally. Although some of these drugs may be given IV, IM, or subcutaneously, most antihistamines are not administered parenterally because they frequently cause local irritation. Some antihistamines also may be administered topically196,349 or intranasally.526,527,528 Topical use of antihistamines generally is discouraged since sensitivity reactions (e.g., sensitization, hypersensitivity) may result.11,44,50,149,151,345,355,356,357,358,359,368,379,380 In addition, topical preparations containing diphenhydramine should not be used more often than directed for any condition, applied on large areas of the body, or used concomitantly with other preparations containing diphenhydramine, including those used orally,672 since increased serum concentrations of diphenhydramine may occur that can result in CNS toxicity.556,575,576 (See Acute Toxicity: Manifestations.) Topical diphenhydramine also should not be used for self-medication in the management of varicella (chickenpox) or measles without first consulting a clinician.672

Dosage !!navigator!!

Dosage of antihistamines should be individualized according to the patient's response and tolerance.

Cautions

[Section Outline]

Adverse effects, which vary in incidence and severity with the individual drug, are caused by all antihistamines, although serious toxicity rarely occurs. Individual patients vary in their susceptibility to the adverse effects of these drugs, and such effects may disappear despite continued therapy. Geriatric patients may be particularly susceptible to dizziness, sedation, and hypotension. Most mild reactions may be relieved by a reduction in dosage or changing to another antihistamine.

Severe cardiovascular effects, including prolongation of the QT interval, arrhythmias, cardiac effects, hypotension, palpitations, syncope, dizziness and/or death have been reported in patients receiving astemizole (no longer commercially available in the US) or terfenadine (no longer commercially available in the US).413,414,415,416,417,418,419,420,421,422,423,431,434,443,444,445,446,447,448,449,466,476,514 These cardiotoxic effects usually were associated with higher than recommended dosages and/or increased plasma concentrations of the drugs and their active metabolites.413,414,416,417,419,421,424,425,426,427,428,429,430,431,432,433,434,448,449,453,454,455,456,457,458,459,461,462,463,464,465,466,476,512,514

CNS Effects !!navigator!!

CNS depression is common with usual dosage of antihistamines, especially with the ethanolamine derivatives. Sedation, ranging from mild drowsiness to deep sleep, occurs most frequently; however, in the treatment of allergies, this effect may be therapeutically useful. Dizziness, lassitude, disturbed coordination, and muscular weakness may also occur. In some patients, the sedative effects disappear spontaneously after the antihistamine has been administered for 2-3 days. Individuals who perform potentially hazardous tasks requiring mental alertness or physical coordination (e.g., operating machinery, driving a motor vehicle) should be warned about possible drowsiness, dizziness, or weakness.705,706 Patients also should be warned to avoid consuming alcoholic beverages while taking antihistamines, since alcohol may potentiate these CNS effects.169,350,390,407,509,705,706 In addition, patients already receiving other CNS depressants (e.g., sedatives, tranquilizers) should be warned not to undertake self-medication with an antihistamine without first consulting their clinician.350,407,491 Patients using diphenhydramine or doxylamine for self-medication should be warned that the drugs may cause marked drowsiness.100,169,197,350,390 Acrivastine, desloratadine, fexofenadine, loratadine, and, possibly, cetirizine and levocetirizine appear to cause fewer adverse CNS effects, including effects on psychomotor performance and reactivity, than other currently available (first generation) antihistamines and therefore commonly have been referred to as relatively “nonsedating” or second generation antihistamines.154,155,156,159,165,180,181,182,183,184,185,186,187,188,189,190,191,404,405,406,459,470,471,472,473,495,496,497,498,499,516,517,509,695 However, while most second generation antihistamines do not appear to potentiate the effects of CNS depressants, including alcohol,161,192,404,405,406,497,498,499 acrivastine, cetirizine, and levocetirizine may potentiate such effects, although less prominently than first generation antihistamines.494,498,499,509,685

Some patients, especially children, receiving antihistamines may experience paradoxical excitement characterized by restlessness, insomnia, tremors, euphoria, nervousness, delirium, palpitation, and even seizures. There have been several reports of toxic psychosis in children who received concomitant oral and topical diphenhydramine for relief of pruritus associated with varicella (chickenpox), poison ivy, or sunburn.556,557,575,576 (See Acute Toxicity: Manifestations.) In addition, central anticholinergic syndrome characterized by hallucinations, agitation, and confusion occurred in several children receiving usual or excessive dosages of cyproheptadine.662 Patients should be warned that phenindamine may be particularly likely to occasionally cause insomnia and nervousness in some individuals.100,169,350 Antihistamines also may precipitate epileptiform seizures in patients with focal lesions of the cerebral cortex, and the drugs should be administered with caution in patients with seizure disorders.

An acute dystonic reaction, which consisted of trismus, difficulty in swallowing, dysarthria, rigidity, and motor incoordination, and was accompanied by mental confusion and tremors, was reported in at least 1 patient receiving IV diphenhydramine.409

GI and Hepatic Effects !!navigator!!

Adverse GI effects of antihistamines include epigastric distress, anorexia, nausea, vomiting, diarrhea, or constipation. GI symptoms may be decreased by administering the drug with meals or with milk. Cholestasis,392,393,395 hepatitis,392,393,394 hepatic failure,391 hepatic function abnormality,391 and jaundice391,392,393,394,395,396 have been reported rarely in patients receiving antihistamines (e.g., cyproheptadine, terfenadine).

Sensitivity Reactions !!navigator!!

Antihistamines can cause sensitivity reactions (e.g., sensitization, hypersensitivity) following topical application11,44,50,149,151,345,349,355,356,357,358,359,360,361,362,363,364,368,369,370,379,380 or systemic administration,50,149,151,345,360,361,364,369,370,379,381,382,383,388,436 but such reactions are more likely following topical use of the drugs,149,151,345,349,355,356,361,364,369,370,379 especially ethylenediamine derivatives.44,50,355,356,361,362,379,380 Antihistamines can act as haptens349 and cause IgE-mediated (type I) hypersensitivity reactions349,369,381,383,388 or T cell-mediated (type IV) sensitization reactions.44,50,149,349,355,356,359,360,361,362,379 Type I reactions appear to occur rarely, but type IV reactions occur more frequently, particularly following topical application of the drugs.149,349,355,356,361,363,364,369,379,381,383 Sensitization following topical use of antihistamines results in allergic contact dermatitis, which may be manifested as eczema, pruritus, and inflammation, at the site of application.44,50,349,355,356,359,360,361,362,363,364,368,379,380 Once local sensitization to an antihistamine occurs, the dermatitis can recur following subsequent topical or systemic exposure to the drug44,50,355,360,361,364,379 or a chemically related drug (including local anesthetics).44,50,355,356,360,361,364,379 Photosensitivity (principally photoallergic dermatitis) reactions, which may be manifested as eczema, pruritus, papular rash, and erythema on exposed skin, also have occurred following topical365,366 or systemic administration365,367,509 of antihistamines, and cross-sensitivity with chemically related drugs can occur.367

Cardiovascular Effects !!navigator!!

Although antihistamines exhibit anticholinergic and local anesthetic effects, including quinidine-like effects on cardiac conduction, and certain drugs have been investigated for potential antiarrhythmic activity, adverse cardiovascular effects are uncommon and usually limited to overdosage situations. When adverse cardiac effects have occurred, they generally were characteristic anticholinergic and/or local anesthetic (quinidine-like) effects such as tachycardia, palpitation, ECG changes (e.g., widened QRS), and arrhythmias (e.g., extrasystole, heart block). Other cardiovascular effects reported with antihistamines include hypotension and hypertension; in some cases, hypotension may result in part from α-adrenergic blocking activity of the antihistamine.

Serious cardiac effects, including prolongation of the QT interval corrected for rate (QTc), ST-U abnormalities, arrhythmias (e.g., ventricular tachycardia, atypical ventricular tachycardia [torsades de pointes], ventricular fibrillation, heart block), arrest, hypotension, palpitations, syncope, dizziness, and/or death (secondary to ventricular tachyarrhythmia), have been reported rarely in patients receiving terfenadine413,414,415,416,417,418,419,420,421,422,423,431,434,443,444,445,446,447,448,449,466,476,514 or astemizole.424,425,426,427,428,429,430,431,432,433,434,448,449,453,456,457,458,459,460,461,462,463,507,512 Astemizole and terfenadine are no longer commercially available in the US.456,659,660 These cardiotoxic effects usually were associated with higher than recommended dosages and/or increased plasma concentrations of the drugs and their active metabolites,413,414,416,417,419,421,424,425,426,427,428,429,430,431,432,433,434,448,449,453,459,461,466,476,514 although serious cardiac effects also have been reported occasionally at usual astemizole or terfenadine dosages.413,414,417,418,424,433,448,449,456,459,461,476,512 While patients with impaired liver function and, possibly, geriatric patients may have been at particular risk of accumulation of these antihistamines and associated cardiotoxic effects,413,417,418,419,422,424,433,447,448,449,456,459,466,476,512 these effects have been reported rarely in apparently healthy individuals with no associated risk factors.413,414,417,418,476

Patients who were receiving concomitant therapy with an azole (including imidazole derivative [e.g., ketoconazole] and triazole derivative [e.g., itraconazole]) antifungal, a macrolide (e.g., clarithromycin, erythromycin, troleandomycin) anti-infective, mibefradil (no longer commercially available in the US), quinine, or grapefruit juice also appeared to be at substantial risk of such toxicity, probably secondary to interference with metabolism of the antihistamine.413,415,416,417,418,419,420,421,423,443,444,445,446,447,448,449,455,456,457,458,459,460,466,475,476,477,479,480,487,490,507,511,512,513,515,518,542,543,544 In addition, concomitant use of terfenadine or astemizole with most human immunodeficiency virus (HIV) protease inhibitors, quinupristin and dalfopristin, zileuton, or serotonin-reuptake inhibitors has not been recommended since HIV protease inhibitors, quinupristin and dalfopristin, zileuton, and serotonin-reuptake inhibitors have been associated with increased plasma concentrations of these antihistamines and potentially serious and/or life-threatening adverse effects could have occurred as a result of these drugs' effects on the metabolism of astemizole or terfenadine.413,518,545,546,547,548,549,550,551,552,553,554,574,664

The potential for similar drug interactions and cardiac effects with loratadine remains to be elucidated more fully.470,505,506 However, acrivastine and loratadine have not been shown to prolong the QT interval when administered alone.487 Prolongation of the QTc interval has been reported in a limited number of healthy adults receiving desloratadine dosages of 45 mg daily (9 times the recommended daily dosage) for 10 days; however, the manufacturer states that no clinically relevant adverse events were reported.670

The manufacturer of cetirizine states that no clinically important prolongation of the QTc interval has been reported in healthy adult men receiving cetirizine during controlled clinical studies.509 The manufacturer of levocetirizine (the R enantiomer of cetirizine) states that no clinically important prolongation of the QTc interval has been reported following administration of a single dose of levocetirizine.685 The effects of multiple-dose administration are not known, but levocetirizine is not expected to have clinically important effects on the QTc interval based on results of QTc studies with cetirizine and the lack of reports of QTc interval prolongation during postmarketing surveillance of that drug.685 The manufacturer of cetirizine also states that concomitant administration of the antihistamine with drugs known to inhibit cytochrome P-450 microsomal enzymes (e.g., azithromycin, erythromycin, ketoconazole) has not been associated with clinically important changes in ECG parameters (e.g., QTc intervals) and that no clinically important interactions have been reported in patients receiving cetirizine concomitantly with azithromycin, erythromycin, or ketoconazole.509,580,584

The manufacturer of fexofenadine states that no statistically significant mean increases in the QTc interval have been reported in healthy adults or patients with seasonal allergic rhinitis receiving fexofenadine hydrochloride dosages up to 400 mg twice daily (for 6 days) or 60-240 mg twice daily (for 2 weeks), respectively, during controlled clinical studies.516,517

The mechanism of the cardiotoxic effects of astemizole and terfenadine has not been fully understood,417,425,426,461,462,466,476 and it appeared to be contrary to what would have been expected from studies on cardiac histamine H1-receptors;426,439,463,464,465 the possibility that H3-receptors (mediating a regulatory feedback mechanism) may have been involved had been suggested.426 Limited evidence from animal models using terfenadine has suggested that the cardiotoxic effects of the drug may have resulted at least in part from blockade of the potassium channel involved in repolarization of cardiac cells (i.e., blockade of the delayed rectifier potassium current IK).455,462,476,514,516 Unlike other antihistamines, anticholinergic and/or local anesthetic effects appeared to be unlikely causes of the cardiac effects of these 2 second generation (relatively “nonsedating”) antihistamines.426

It has been recommended that usual dosages of terfenadine (i.e., 60 mg twice daily) and astemizole (i.e., 10 mg daily) not be exceeded because of the risk of potentially life-threatening cardiotoxic effects.413,417,419,430,433,448,449,459,476 Because of this risk, patients were advised not to temporarily increase (e.g., double) the prescribed dosage in an attempt to accelerate or improve symptomatic relief provided by these drugs.413,419,424,433,448,449,459,476

Patients with hepatic impairment, geriatric patients, those receiving drugs or who had underlying conditions that might have prolonged the QT interval, and those who were receiving drugs that could have produced electrolyte abnormalities such as hypokalemia or hypomagnesemia may have been at increased risk of cardiac arrhythmias during terfenadine or astemizole therapy.413,419,424,433,448,449,459,466,475,476,477 Therefore, administration of these antihistamines was not recommended in such patients.413,419,424,433,448,449,459,476,477 Terfenadine or astemizole also should not have been used in patients receiving a macrolide (e.g., clarithromycin, erythromycin, troleandomycin) anti-infective, an azole antifungal (including imidazole [e.g., itraconazole] and triazole [e.g., itraconazole] derivatives), or mibefradil; in addition, use of these antihistamines in patients receiving any other drug (e.g., quinine, most HIV protease inhibitors, serotonin-reuptake inhibitors, zileuton) that potentially could inhibit their metabolism was not recommended.413,416,417,418,419,447,448,449,455,459,466,475,476,490,508,513,514,518,545,546,547,548,549,550,551,552,553,554,574 It also has been recommended that astemizole or terfenadine not be taken with grapefruit juice.413,512 Concomitant administration of astemizole with therapeutic doses of quinine was contraindicated.511,512,513,514

Other Adverse Effects !!navigator!!

Adverse anticholinergic effects of antihistamines include dryness of mouth, nose, and throat; dysuria; urinary retention; impotence; vertigo; visual disturbances; blurred vision; diplopia; tinnitus; acute labyrinthitis; insomnia; tremors; nervousness; irritability; and facial dyskinesia. Tightness of the chest, thickening of bronchial secretions, wheezing, nasal stuffiness, sweating, chills, early menses, toxic psychosis, headache, faintness, and paresthesia have occurred.

Rarely, agranulocytosis, hemolytic anemia, leukopenia, thrombocytopenia, and pancytopenia have been reported in patients receiving some antihistamines. Increased appetite and/or weight gain also occurred in patients receiving antihistamines (cyproheptadine).

Precautions and Contraindications !!navigator!!

Antihistamines having substantial anticholinergic activity (usually conventional [prototypical, first generation] including ethanolamines) should be administered with caution, if at all, in patients with angle-closure glaucoma, prostatic hypertrophy (which may result in difficulty in urination), stenosing peptic ulcer, pyloroduodenal obstruction, or bladder neck obstruction. Because it was suggested that the anticholinergic effect of antihistamines might reduce the volume and cause thickening of bronchial secretions and thus result in obstruction of respiratory passages, it had been recommended that the drugs be used with caution and only under the direction of a clinician in patients with asthma or chronic obstructive pulmonary disease if clearance of bronchial secretions was a problem.169,467,487 While some clinicians100,481,482 and manufacturers320,391,411,484,487 continue to warn against use of the drugs in patients with asthma because of potential effects of anticholinergic activity on the volume and fluidity of bronchial secretions, most experts467,486,500 and clinicians382,481,482,484,487 believe that there currently is little, if any, direct evidence of antihistamine-induced exacerbation of asthma secondary to bronchial drying nor substantiation for avoiding use of currently available antihistamines in asthmatic patients.467,481,500 Antihistamines usually should not be used, unless under the direction of a clinician, in patients who have a breathing problem (e.g., emphysema, chronic bronchitis),467,485,486 and these drugs generally should not be used in asthmatics who previously experienced a serious antihistamine-induced adverse bronchopulmonary effect.467,481 467,481 In addition, antihistamines should be used with caution in patients with increased intraocular pressure, hyperthyroidism, cardiovascular disease, or hypertension. The drugs are contraindicated in patients with asthmatic attacks. For self-medication , cough preparations containing an antihistamine (e.g., diphenhydramine) should not be used for persistent or chronic cough or breathing problems such as those occurring with smoking, asthma, chronic bronchitis, or emphysema, or for cough accompanied by excessive phlegm, unless directed by a clinician.501 A persistent cough may be indicative of a serious condition.501 If cough persists for more than one week, is recurrent, or is accompanied by fever, rash, or persistent headache, a clinician should be consulted.501

Patients should be advised that CNS depression (e.g., drowsiness) is common with first generation antihistamines, even at usual dosages and particularly with ethanolamine derivatives. (See Cautions: CNS Effects.) In addition, patients should be warned that additive CNS depression may occur when first generation antihistamines or possibly, cetirizine or levocetirizine is administered concomitantly with other CNS depressants, including alcohol.685 (See Drug Interactions: CNS Depressants.) Patients receiving acrivastine, a second generation antihistamine, also should be warned of the possibility of such effects.494,498,499

Diphenhydramine toxicity (e.g., dilated pupils, facial flushing, hallucinations, ataxic gait, urinary retention) has been reported in pediatric patients following topical application of diphenhydramine to large areas of the body (often areas with broken skin) or following concomitant use of topical and oral preparations containing diphenhydramine.556 (See Acute Toxicity: Manifestations.) Therefore, the US Food and Drug Administration (FDA) and many clinicians warn that oral diphenhydramine should not be used concomitantly with any other preparations containing the drug, including those used topically.556,672 (See Cautions, in Diphenhydramine 4:04.) In addition, topical preparations containing diphenhydramine should not be used more often than directed for any condition, applied on large areas of the body, or used concomitantly with other preparations containing diphenhydramine, including those used orally,672 since increased serum concentrations of diphenhydramine may occur that can result in CNS toxicity.556,557,575,576 (See Acute Toxicity: Manifestations.) Patients should be advised to consult a clinician prior to use of topical diphenhydramine for the management of varicella (chickenpox) or measles.672

Although diphenhydramine appears to have low abuse potential, several children, adolescents, and at least one adult with chronic hematologic and antineoplastic diseases have exhibited drug-seeking behavior and anticholinergic effects after chronic intermittent rapid IV administration of the drug.661

While astemizole and terfenadine were commercially available in the US, individuals receiving these second generation antihistamines were warned that patients with hepatic impairment (e.g., cirrhosis, hepatitis); geriatric patients; those who were concomitantly receiving an azole-derivative anti-infective (e.g., fluconazole, itraconazole, ketoconazole, metronidazole, miconazole), a macrolide antibiotic (e.g., clarithromycin, erythromycin, troleandomycin), mibefradil (no longer commercially available in the US), or other potent inhibitors of the cytochrome P-450 isoenzyme (CYP3A) (including most HIV protease inhibitors, quinupristin and dalfopristin, zileuton, or serotonin-reuptake inhibitors) responsible for the metabolism of astemizole or terfenadine (see Drug Interactions); those who were having underlying conditions that might prolong the QT interval corrected for rate (QTc) (e.g., hypokalemia, hypomagnesemia, bradycardia, congenital QT syndrome); those who were receiving drugs that might prolong the QTc interval (e.g., certain antiarrhythmic agents, bepridil hydrochloride, certain psychotropic agents, probucol [no longer commercially available in the US], cisapride, sparfloxacin, pentamidine); or those who were receiving drugs (e.g., diuretics) that could produce electrolyte abnormalities, such as hypokalemia or hypomagnesemia, may have experienced prolongation of the QTc interval and may have been at increased risk of cardiac arrhythmias (e.g., ventricular tachycardia, atypical ventricular tachycardia [torsades de pointes], ventricular fibrillation) when they were receiving recommended dosages of astemizole or terfenadine.416,434,457,458,466,475,476,477,478,512,515,594,595,596,597,605,606,607,615,643,645,646,658,664 Therefore, administration of astemizole or terfenadine was not recommended in such patients.434,477,512,594,597,605,606,643,664

In addition, astemizole or terfenadine was contraindicated in patients with disease states (e.g., severe hepatic impairment) or receiving concomitant therapy (e.g., itraconazole, ketoconazole, clarithromycin, erythromycin, troleandomycin, mibefradil) known to impair metabolism of the antihistamine.419,443,477,510,512,594,596,597,605,606,607,634 Astemizole also was contraindicated in patients receiving concomitant therapy with quinine.512

For additional cautions, contraindications, and drug interactions with the phenothiazine derivatives, see the Phenothiazines General Statement 28:16.08.24.

Pediatric Precautions !!navigator!!

Antihistamines should not be administered to premature or full-term neonates. Young children may be more susceptible than adults to the toxic effects of antihistamines.307,308 (See Acute Toxicity.) Adults responsible for the supervision of a child receiving an antihistamine should be warned that children may be at increased risk for experiencing CNS stimulant effects with antihistamines.100,169,307 (See Cautions: CNS Effects.) Although the relationship and possible mechanism(s) have not been elucidated,203,204,205,206,207 respiratory depression, sleep apnea, and sudden infant death syndrome (SIDS) have occurred in a number of infants and young children who were receiving usual dosages of phenothiazine-derivative antihistamines (i.e., promethazine, trimeprazine [no longer commercially available in the US]).202,203,206,207 (See Cautions: Pediatric Precautions, in Promethazine 4:04.) In addition, death has been reported in children younger than 2 years of age receiving carbinoxamine-containing preparations696,697 or cough and cold preparations containing an antihistamine with or without other agents (e.g., cough suppressants, expectorants, nasal decongestants).693 (See Uses: Regulations Governing Carbinoxamine-containing Preparations, in Carbinoxamine Maleate 4:04 and also see Cautions: Pediatric Precautions, in Pseudoephedrine Hydrochloride 12:12.12.)

In a report published by the US Centers for Disease Control and Prevention (CDC), cough and cold preparations containing carbinoxamine, pseudoephedrine, acetaminophen, and/or dextromethorphan were determined by medical examiners or coroners to be the underlying cause of death in 3 infants 6 months of age or younger during 2005.693,694 The actual cause of death might have been overdosage of one drug, interaction of different drugs, an underlying medical condition, or a combination of drugs and underlying medical conditions.693 In addition, an estimated 1519 children younger than 2 years of age were treated in emergency departments in the US during 2004-2005 for adverse events, including overdoses, associated with cold and cough preparations.693

The dosages at which cold and cough preparations can cause illness or death in pediatric patients younger than 2 years of age are not known, and there are no specific dosage recommendations (i.e., approved by the US Food and Drug Administration [FDA]) for the symptomatic treatment of cold and cough for patients in this age group.693 Because of the absence of dosage recommendations, limited published evidence of effectiveness, and risks for toxicity (including fatal overdosage).693,694 FDA stated that nonprescription cough and cold preparations should not be used in children younger than 2 years of a 699 the agency continues to assess safety and efficacy of these preparations in older children.702,704 Meanwhile, because children 2-3 years of age also are at increased risk of overdosage and toxicity, some manufacturers of oral nonprescription cough and cold preparations agreed to voluntarily revise the product labeling to state that such preparations should not be used in children younger than 4 years of age.701,702,703,704 FDA recommends that parents and caregivers adhere to the dosage instructions and warnings on the product labeling that accompanies the preparation if administering to children and consult with their clinician about any concerns.701,702,703 Clinicians should ask caregivers about use of nonprescription cough and cold preparations to avoid overdosage.693

Because antihistamines may cause drowsiness that can be potentiated by other CNS depressants (e.g., sedatives, tranquilizers), an antihistamine should be used in children receiving one of these drugs only under the direction of a clinician.350 Antihistamines should not be used in children who have a breathing problem (e.g., chronic bronchitis) or glaucoma unless otherwise directed by a clinician.485 It also has been recommended that antihistamines not be used in children with asthma, liver disease, or seizure disorder unless under the direction of a clinician.390 Overdosage of doxylamine has been reported in children.705,706 Manifestations of doxylamine overdosage in children have included coma, generalized tonic-clonic (grand mal) seizures, cardiorespiratory arrest, and death.705,706 Children appear to be at high risk for cardiorespiratory arrest secondary to doxylamine overdosage.705,706 For additional information, see the individual monographs in 4:00.

Acute toxicity has been reported in pediatric patients following topical application of diphenhydramine to large areas of the body (often areas with broken skin) or following concomitant use of topical and oral preparations containing diphenhydramine.556 (See Cautions: Precautions and Contraindications, and also see Acute Toxicity.)

While it is desirable to avoid the use of alcohol-containing antihistamine preparations in children because of potential toxicity,100,390,403 inclusion of alcohol in some preparations may be a pharmaceutical necessity (e.g., as a solvent) and therefore complete avoidance of such preparations may not be possible.390,403 According to a final rule issued in 1995 by FDA, over-the-counter (OTC) oral preparations intended for use in children younger than 6 years of age, children 6-11 years of age, or children 12 years of age and older may contain up to 0.5, 5, or 10% alcohol, respectively.678,679

Pregnancy and Lactation !!navigator!!

Pregnancy

Antihistamines should not be used in women who are or may become pregnant unless the potential benefits justify the possible risks to the fetus. Some manufacturers caution that antihistamines should not be used during the third trimester because of the risk of severe reactions (e.g., seizures) to the drugs in neonates and premature infants.143,320 For additional information, see the individual monographs in 4:00.

Doxylamine succinate in fixed combination with pyridoxine hydrochloride is intended for use in the management of nausea and vomiting of pregnancy.705,706,710 Historically, there was considerable controversy regarding the teratogenic potential, if any, of doxylamine succinate;169,268,269,270,271,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,289,290,291,292,293,294,295,296,297,298,299,300,301,302,303,304,305,306,350 however, after evaluating extensive data and information concerning the possible teratogenicity of the drug, FDA concluded that it is unlikely that doxylamine succinate is teratogenic.350 In addition, FDA states that the removal of products containing doxylamine succinate that previously were commercially available for the management of nausea and vomiting of pregnancy was not for reasons of safety or effectiveness.709 Numerous epidemiologic studies (including cohort studies, case-control studies, and meta-analyses) have been performed to investigate possible teratogenic effects of doxylamine succinate in fixed combination with pyridoxine hydrochloride in pregnant women and have found no evidence of an increased risk of fetal malformations.705,706,711,712

Lactation

Most manufacturers state that antihistamines should not be administered to nursing women, since the drugs may inhibit lactation and small amounts appear to be distributed into milk. Adverse effects (e.g., excitement, irritability, and sedation) have been reported in infants presumably exposed to antihistamines (e.g., doxylamine) through human milk.705,706 Infants with apnea or other respiratory syndromes may be particularly vulnerable to the sedative effects of antihistamines (e.g., doxylamine).705,706

Because of the potential for serious adverse reactions (e.g., CNS effects) to antihistamines in nursing infants, a decision should be made whether to discontinue nursing or antihistamines, taking into account the importance of the drugs to the woman. The manufacturer of doxylamine in fixed combination with pyridoxine states that this preparation should not be used in nursing women.705,706

Drug Interactions

[Section Outline]

CNS Depressants !!navigator!!

Additive CNS depression may occur when antihistamines are administered concomitantly with other CNS depressants including barbiturates, tranquilizers, and alcohol. If antihistamines are used concomitantly with other depressant drugs, caution should be used to avoid overdosage. Patients should be advised to avoid alcoholic beverages during antihistamine therapy.350,407,585,586 Patients already receiving another CNS depressant (e.g., sedatives, tranquilizers) should not undertake self-medication with an antihistamine without first consulting a physician.350,407,585,586 Unlike first generation antihistamines, most second generation antihistamines (e.g., astemizole [no longer commercially available in the US], loratadine, terfenadine [no longer commercially available in the US]) do not appear to potentiate the sedative effects of CNS depressants;161,192,404,405,406,456,497,498,499,659,660 however, acrivastine, cetirizine, and levocetirizine, which also have been classified as second generation antihistamines, may potentiate such effects, although less prominently than first generation antihistamines.494,498,499,509,685

It also should be considered that monoamine oxidase (MAO) inhibitors may prolong and intensify some anticholinergic effects (e.g., dryness) of antihistamines.705,706 The manufacturer of doxylamine in fixed combination with pyridoxine hydrochloride states that the drug is contraindicated in patients receiving MAO inhibitors.705,706

Epinephrine !!navigator!!

Phenothiazine-type antihistamines (e.g., methdilazine [no longer commercially available in the US], promethazine, trimeprazine [no longer commercially available in the US]) may block and reverse the vasopressor effect of epinephrine. If patients receiving phenothiazines require a vasopressor agent, norepinephrine or phenylephrine should be used; epinephrine should not be used.

Drugs and Foods Affecting Hepatic Microsomal Enzymes !!navigator!!

Concomitant administration of astemizole or terfenadine with drugs that can inhibit the metabolism of these antihistamines has resulted in accumulation of potentially cardiotoxic concentrations of astemizole or terfenadine and/or their active metabolites.413,416,417,418,419,447,448,449,454,456,457,458,459,460,466,477,508 (See Cautions: Cardiovascular Effects.) Both human and animal data have indicated that associated cardiotoxic effects resulted principally from accumulation of unchanged astemizole (and its main metabolite desmethylastemizole) or unchanged terfenadine.466,476,477,478,512,541,596,597,605,606,607,615,616,617,638

Serious, potentially life-threatening cardiac effects have occurred when astemizole or terfenadine was used concomitantly with certain azole antifungal (including imidazole derivative [e.g., ketoconazole] and triazole derivative [e.g., itraconazole]) or macrolide (e.g., clarithromycin, erythromycin, troleandomycin) anti-infectives, mibefradil (no longer commercially available in the US), or quinine sulfate (a single dose of 430 mg), probably secondary to inhibition of metabolism of the antihistamine by these drugs.413,415,416,417,418,419,420,421,423,443,444,445,446,447,448,449,454,455,456,457,458,459,460,466,475,476,477,490,508,511,512,513,514,515 Therefore, while astemizole or terfenadine was commercially available in the US,456,659,660 concomitant therapy with these or other known inhibitors of astemizole or terfenadine metabolism was contraindicated.416,418,419,447,448,449,477,512,594,596,597,605,606,607,643 No clinically adverse effects or changes in the QTc intervals were reported after concomitant administration of erythromycin or ketoconazole with fexofenadine, the active metabolite of terfenadine.516,517 The increased safety profile of fexofenadine compared with the parent drug, terfenadine, may result from the lack of fexofenadine-induced cardiotoxicity in addition to only minimal metabolism of fexofenadine in the liver by the cytochrome P-450 microsomal enzyme system.514,516,517

Concomitant use of terfenadine or astemizole with other chemically related azole-derivative anti-infective (e.g., fluconazole, miconazole, metronidazole), most human immunodeficiency virus (HIV) protease inhibitors, quinupristin and dalfopristin, zileuton, or serotonin-reuptake inhibitors has not been recommended since these drugs may have increased plasma concentrations of terfenadine and/or astemizole and potentially serious and/or life-threatening adverse effects could have occurred.413,518,545,546,547,548,549,550,551,552,553,554,574,664

Grapefruit juice also may have inhibited metabolism of terfenadine.413,514,518,541,544,555 Increased oral bioavailability of unchanged terfenadine observed with concomitant administration of the drug and grapefruit juice has been associated with prolongation of the QT interval averaging 3.3% (range: -1.6 to 9.5%);541 mean QT interval corrected for rate (QTc) increased by 4-14 msec compared with administration of terfenadine with water.413,514,518,541,544,555 Therefore, it has been recommended that astemizole or terfenadine not be taken concomitantly with grapefruit juice.512,596,607

Ketoconazole and Other Azole Antifungal Agents

Prolongation of the QT interval and QT interval corrected for rate (QTc) and, rarely, serious cardiovascular effects, including arrhythmias (e.g., ventricular tachycardia, atypical ventricular tachycardia [torsades de pointes, ventricular fibrillation]), cardiac arrest, palpitations, hypotension, dizziness, syncope, and death, have been reported in patients receiving recommended dosages of astemizole or terfenadine concomitantly with ketoconazole.416,418,419,420,434,443,458,475,476,512,515,594,595,596,597,598,599,605,606,607,643 Ketoconazole has markedly inhibited the metabolism of astemizole or terfenadine, probably via inhibition of the cytochrome P-450 microsomal enzyme system, which resulted in increased plasma concentrations of unchanged astemizole (and its principal metabolite desmethylastemizole) or unchanged terfenadine; clearance of the active carboxylic acid metabolite of terfenadine also may have been reduced.434,458,475,476,477,512,597,598,605,643 Increased plasma concentrations of unchanged astemizole (and its principal metabolite desmethylastemizole) or unchanged terfenadine has been associated with prolongation of the QT and QTc intervals.416,419,420,443,458,475,476,477,512,594,597,599,605,643 Similar alterations in astemizole or terfenadine pharmacokinetics and adverse cardiac effects (prolongation of the QTc interval, cardiac arrest, and ventricular arrhythmias [e.g., torsades de pointes]) have been reported in patients receiving the antihistamine concomitantly with itraconazole.457,477,478,490,512,594,596,605,607,612 Therefore, while commercially available in the US,456,659,660 astemizole and terfenadine were contraindicated in patients receiving ketoconazole or itraconazole.418,457,458,477,512,515,594,605,643 In addition, it has been recommended that astemizole and terfenadine also not be used in patients receiving drugs that are structurally related to these antifungals (e.g., triazoles such as fluconazole, imidazoles such as miconazole, nitroimidazoles such as metronidazole).512,594,596,597,607

Increased plasma concentrations of loratadine and its active metabolite desloratadine (descarboethoxyloratadine) also have been reported in controlled clinical studies in healthy men receiving 10 mg of loratadine once daily concomitantly with ketoconazole dosages of 200 mg every 12 hours.470,502 In these studies, area under the plasma concentration-time curve (AUC) of loratadine increased by 307% following concomitant administration with ketoconazole while AUC of desloratadine increased by 73% following concomitant administration with ketoconazole.470,502 However, no clinically important changes, as measured by ECG and laboratory evaluations, vital signs, and adverse effects, were reported after concomitant administration of ketoconazole with loratadine.470 In addition, no changes in QTc intervals, sedation, or syncope were reported in these individuals.470,502 Plasma concentrations of ketoconazole appeared to be unchanged in individuals receiving loratadine concomitantly.470 In addition, increased plasma concentrations of loratadine (AUC increased by 180%) and desloratadine (AUC increased by 56%) have been reported in a limited number of individuals receiving a single 20-mg dose of loratadine concomitantly with a ketoconazole dosage of 200 mg twice daily.488,502 However, no changes in QTc intervals were reported 2, 6, and 24 hours after concomitant administration of the drugs.488,502 Adverse effects were similar in individuals receiving loratadine alone compared with those receiving loratadine concomitantly with ketoconazole.488,502

Increased plasma concentrations of desloratadine and 3-hydroxydesloratadine have been reported in a controlled clinical study in healthy individuals receiving 7.5 mg of desloratadine once daily concomitantly with ketoconazole dosages of 200 mg every 12 hours for 10 days.670 In this study, AUC of desloratadine or 3-hydroxydesloratadine increased by 39 or 72%, respectively, while peak plasma concentrations increased by 45 or 43%, respectively, following concomitant administration with ketoconazole.670 However, no clinically important changes, as measured by ECG and laboratory evaluations, vital signs, and adverse effects, were reported after concomitant administration of ketoconazole with desloratadine.670

The manufacturer of cetirizine states that no clinically important drug interactions have been reported in patients receiving cetirizine concomitantly with ketoconazole.509

Increased plasma concentrations of fexofenadine have been reported in 2 studies in healthy individuals receiving 120 mg of fexofenadine twice daily concomitantly with ketoconazole 400 mg once daily.516 In these studies, AUC of fexofenadine increased by 164% following concomitant administration with ketoconazole while peak plasma concentrations of fexofenadine increased by 135%.516 However, no clinically important adverse effects or changes in the QTc intervals were reported after concomitant administration of ketoconazole with fexofenadine.516,517

Macrolides

Erythromycin and clarithromycin have altered the metabolism of astemizole or terfenadine.419,434,443,445,466,477,507,512,515,594,596,597,606,607,613,643 In some individuals, concomitant administration of erythromycin with astemizole or terfenadine has resulted in increased plasma concentrations of unchanged astemizole (and its principal metabolite desmethylastemizole) or unchanged terfenadine (and its active carboxylic metabolite fexofenadine).512,596,606,607 Prolongation of the QTc, ST-U abnormalities, and ventricular tachycardia, including torsades de pointes, have been reported in some patients receiving astemizole or terfenadine concomitantly with erythromycin or the structurally related macrolides clarithromycin, troleandomycin, or josamycin.416,434,445,446,447,448,449,466,476,507,512,594,596,597,606,607,655 Cardiac arrest and death have occurred in patients receiving erythromycin concomitantly with astemizole or terfenadine.510,512,606 Therefore, while commercially available in the US,456,659,660 astemizole or terfenadine was contraindicated in patients receiving clarithromycin, erythromycin, or troleandomycin.416,418,446,448,449,477,512,515,582,594,606,613,655

Limited data have suggested that azithromycin606,607,608,610,611,632 and dirithromycin606,609,633 did not appear to alter the metabolism of terfenadine.593,606,608,609,610,611,633

Increased plasma concentrations of loratadine and its active metabolite desloratadine have been reported in controlled clinical studies in healthy men receiving 10 mg of loratadine once daily concomitantly with erythromycin dosages of 500 mg every 8 hours for 10 days.470,502,503 In these studies, AUC of loratadine increased by 40% following concomitant administration with erythromycin, while AUC of desloratadine increased by 46%.470,502,503 However, no clinically important changes, as measured by ECG and laboratory evaluations, vital signs, and adverse effects, were reported after concomitant administration of erythromycin with loratadine.470,503 In addition, no changes in QTc intervals, sedation, or syncope were reported in these individuals.470,502,503 Although the clinical importance has not been established, decreased plasma concentrations of erythromycin (AUC decreased by 15-18%) have been reported in these patients receiving loratadine concomitantly.470,503

Increased plasma concentrations of loratadine and desloratadine also have been reported in a controlled drug interaction study in healthy men receiving 10 mg of loratadine every 24 hours concomitantly with clarithromycin dosages of 500 mg every 12 hours for 10 days.663 In this study, peak steady-state plasma concentrations and AUC of loratadine increased by 36 and 76%, respectively, following concomitant administration with clarithromycin for 10 days while peak steady-state plasma concentrations and AUC of desloratadine increased by 69 and 49%, respectively, compared with administration of loratadine alone.663 Although mean maximum QTc interval was modestly increased (by less than 3% and not exceeding 439 msec) when loratadine was administered concomitantly with clarithromycin, such increase was similar to that observed when loratadine was administered alone and probably was not clinically important.663 The pharmacokinetics of clarithromycin were not affected by concomitant loratadine.663

Increased plasma concentrations of desloratadine and 3-hydroxydesloratadine have been reported in a controlled clinical study in healthy individuals receiving 7.5 mg of desloratadine once daily concomitantly with erythromycin dosages of 500 mg every 8 hours for 10 days.670 In this study, AUC of desloratadine or 3-hydroxydesloratadine increased by 14 or 40%, respectively, while peak plasma concentrations increased by 24 or 43%, respectively, following concomitant administration with erythromycin.670 In another study in healthy individuals receiving 5 mg of desloratadine once daily concomitantly with azithromycin (500 mg followed by 250 mg once daily for 4 days), AUC of desloratadine or 3-hydroxydesloratadine increased by 5 or 4%, respectively, while peak plasma concentrations increased by 15%.670 However, no clinically important changes, as measured by ECG and laboratory evaluations, vital signs, and adverse effects, were reported after concomitant administration of erythromycin or azithromycin with desloratadine.670

The manufacturer of cetirizine states that no clinically important drug interactions have been reported in patients receiving cetirizine concomitantly with azithromycin or erythromycin.509

Increased plasma concentrations of fexofenadine have been reported in 2 studies in healthy individuals receiving 120 mg of fexofenadine twice daily concomitantly with erythromycin dosages of 500 mg every 8 hours.516 In these studies, AUC of fexofenadine increased by 109% following concomitant administration with erythromycin, while peak plasma concentrations of fexofenadine increased by 82%.516 However, no clinically important adverse effects or changes in the QTc intervals were reported after concomitant administration of erythromycin with fexofenadine.516,517

HIV Protease Inhibitors

In vitro, ritonavir has been shown to inhibit the metabolism of terfenadine, but the clinical importance of this in vitro finding is not known.596,607 Several manufacturers of HIV protease inhibitors and some clinicians state that specific in vivo pharmacokinetic drug interaction studies between these antihistamines and HIV protease inhibitors currently are not available.545,546,547,548,549,554 Concomitant use of astemizole or terfenadine with HIV protease inhibitors (e.g., indinavir, nelfinavir, ritonavir, saquinavir) has not been recommended,512,582,596,607 because of the theoretical risk that the HIV protease inhibitor could produce substantially increased plasma concentrations of unchanged astemizole or terfenadine resulting in potentially serious and/or life-threatening adverse effects.512,545,546,547,548,549,554 The manufacturers of indinavir and ritonavir state that concomitant use of either drug with astemizole or terfenadine is contraindicated because such use may precipitate potentially life-threatening adverse effects.656,657

Serotonin-reuptake Inhibitors

In vitro, fluvoxamine, nefazodone, or sertraline and/or their metabolites have been shown to inhibit metabolism of terfenadine probably secondary to inhibition of the cytochrome P-450 (CYP34A) enzyme system, but the clinical importance of these in vitro findings is not known.553,596,607,641 Concomitant administration of astemizole or terfenadine and any of the serotonin-reuptake inhibitors (i.e., fluoxetine, fluvoxamine, nefazodone, paroxetine, sertraline) has not been recommended since substantially increased plasma concentrations of unchanged astemizole or terfenadine could occur resulting in an increased risk of serious adverse cardiac effects.512,553,582,596,607 The manufacturer of fluvoxamine and some clinicians state that concomitant use of the antidepressant with terfenadine or astemizole is contraindicated.551,552 However, at least one manufacturer (i.e., of sertraline) states that in vivo drug interaction studies with sertraline and terfenadine have failed to confirm any important alteration in plasma terfenadine concentrations by the antidepressant and that a clinically important interaction is unlikely.647

Increased plasma concentrations of desloratadine and 3-hydroxydesloratadine have been reported in a controlled clinical study in healthy individuals who were pretreated with fluoxetine for 23 days prior to receiving 5 mg of desloratadine once daily concomitantly with fluoxetine 20 mg once daily for 7 days.670 In this study, peak plasma concentrations of desloratadine or 3-hydroxydesloratadine increased by 15 or 17%, respectively, while AUC of 3-hydroxydesloratadine increased by 13%, following concomitant administration with fluoxetine.670 However, no clinically important changes, as measured by ECG and laboratory evaluations, vital signs, and adverse effects, were reported after concomitant administration of fluoxetine with desloratadine.670

Zileuton

Increased plasma concentrations of terfenadine have been reported in one study in healthy individuals receiving 60 mg of terfenadine every 12 hours concomitantly with zileuton dosages of 600 mg every 6 hours for 7 days.574,596,607 In this study, AUC and peak plasma concentrations of terfenadine increased by about 35%, resulting from a 22% decrease in the clearance of unchanged terfenadine.574,596,607 Although no adverse cardiac effects (e.g., substantial changes in QTc intervals) were reported in these individuals, concomitant administration of astemizole or terfenadine with zileuton is not recommended since pharmacokinetics of the antihistamines may be impaired resulting in an increased risk of serious adverse cardiac effects.512,574,582,596,607

Quinine and Chemically Related Drugs

There has been some evidence indicating that quinine may alter the pharmacokinetics of astemizole.511,512,614 Quinine is extensively metabolized in the liver; however, only limited information exists about the specific cytochrome P-450 microsomal isoenzymes responsible for the drug's metabolism.615 Increased plasma concentrations of astemizole and desmethylastemizole were reported in a study in healthy men receiving 10 mg of astemizole orally once daily for 24 days and 20 mg of quinine sulfate every 4 hours for 4 consecutive doses on the 22nd day and then a single 430-mg dose on the 24th day of the study.614 In this study, slight increases in the maximum plasma concentration and AUC of astemizole were associated with concomitant administration of the 20-mg doses of quinine sulfate; however, no clinically or statistically significant changes in QT interval were observed.614 Maximum plasma concentrations and AUCs of astemizole and desmethylastemizole increased threefold following concomitant administration of the antihistamine and the 430-mg dose of quinine sulfate; these increases were associated with increases in the QT interval.614 Therefore, the manufacturer of astemizole has stated that concomitant administration of astemizole and therapeutic doses (i.e., more than 80 mg daily) of quinine sulfate were contraindicated.512

Although increases in plasma concentrations of astemizole and its desmethyl metabolite also may occur in patients receiving the antihistamine concomitantly with food products containing quinine (e.g., tonic water), such increases are small and not associated with clinically or statistically significant prolongation of the QT interval when consumption is limited to approximately 1 L (32 oz) of tonic water a day (about 80 mg of quinine sulfate).614 Since consumption of larger daily amounts of quinine in tonic water may be associated with risk in patients receiving astemizole, patients who consume large amounts of tonic water daily may wish to consult their clinician.593

Histamine H2-Receptor Antagonists and Xanthine Derivatives

The manufacturer of terfenadine has stated that detectable plasma concentrations of unchanged terfenadine were not present and mean pharmacokinetic parameters (e.g., AUC, elimination half-life, peak plasma concentration) for the carboxylic acid metabolite fexofenadine did not appear to be affected in a study in which a single dose of terfenadine was given to individuals receiving multiple doses of cimetidine.443,597,604 Other data also suggest that an interaction between the drugs seems unlikely.593 While the potential for such a drug interaction has not been established, cardiotoxic effects also occurred following a terfenadine overdosage in at least one patient who was receiving cimetidine.597 In addition, torsades de pointes and prolongation of QT interval were reported in a patient receiving terfenadine 60 mg twice daily concomitantly with cimetidine 400 mg twice daily, and some clinicians state that concomitant use of terfenadine and cimetidine is not recommended.642,644

Increased plasma concentrations of loratadine and its active metabolite desloratadine have been reported in controlled clinical studies in healthy men receiving 10 mg of loratadine once daily concomitantly with cimetidine dosages of 300 mg 4 times daily (every 6 hours) for 10 days.470,502,503 In these studies, AUC of loratadine increased by 103% following concomitant administration with cimetidine, while AUC of descarboethoxyloratadine increased by 6% following concomitant administration with cimetidine.470,502,503 However, no clinically important changes, as measured by ECG and laboratory evaluations, vital signs, and adverse effects, were reported after concomitant administration of cimetidine with loratadine.470,503 In addition, no changes in QTc intervals, sedation, or syncope were reported in these individuals.470,502,503 Plasma concentrations of cimetidine appeared to be unchanged in individuals receiving loratadine concomitantly.470

Increased plasma concentrations of desloratadine have been reported in a controlled clinical study in healthy individuals receiving 5 mg of the drug once daily concomitantly with cimetidine (600 mg every 12 hours for 14 days under steady-state conditions).670 In this study, peak plasma concentrations and AUC of desloratadine increased by 12 and 19%, respectively, following concomitant administration with cimetidine.670 However, no clinically important changes, as measured by ECG and laboratory evaluations, vital signs, and adverse effects, were reported after concomitant administration of cimetidine with desloratadine.670

Other Drugs

To date, the number of patients receiving loratadine concomitantly with ranitidine or theophylline has been too small to rule out a possible drug interaction between loratadine and such drugs and therefore, the manufacturers have recommended that loratadine be used with caution in patients receiving them.488

Grapefruit Juice

Concomitant oral administration of grapefruit juice with terfenadine has been reported to increase bioavailability of terfenadine.541,542,544,555,596,607,616,617,643,649 This increased bioavailability of terfenadine was associated with prolongation of the QT interval averaging 3.3% (range: -1.6 to 9.5%); mean QTc intervals increased by 4-14 msec compared with administration of terfenadine with water.541,544,555,596,607,615 The interaction between grapefruit juice and terfenadine bioavailability appears to result from inhibition, probably prehepatic,541,544,555,574,616,619,620,621,622,623,624,636,637 of the cytochrome P-450 enzyme system by some constituent(s) in the juice.541,544,574,618,619,620,621,622,623,624,625,626,627,628,629,630,631,636,637 Patients have been discouraged to ingest grapefruit juice concomitantly with terfenadine;541,542 in addition, concomitant administration of astemizole with grapefruit juice has not been recommended since substantially increased plasma concentrations of unchanged astemizole also could occur resulting in an increased risk of serious adverse cardiac effects.512,582

Concomitant oral administration of grapefruit juice with desloratadine does not appear to alter bioavailability of the drug.671

Other Information

[Section Outline]

Laboratory Test Interferences

Antihistamines may suppress inhalation-challenge testing with histamine or antigen as well as the wheal and flare reactions to antigen skin testing.309,310,311,312,313,314,315,316,317 Considerable interindividual variation in the extent and duration of suppression has been reported, depending on the antigen and test technique, antihistamine and dosage regimen, time since the last dose, and individual response to testing.309,311,312,316,317 In one study, usual oral dosages of chlorpheniramine or diphenhydramine suppressed the wheal response for about 2 days after the last dose, promethazine or tripelennamine suppressed whealing for about 3 days, and hydroxyzine suppressed whealing for about 4 days.309 Combined use of an H1- and H2-antagonist appears to have a synergistic suppressive effect on immediate and late cutaneous reactions to skin test antigens.316,317 Whenever possible, antihistamines should be discontinued about 4 days prior to skin testing procedures since they may prevent otherwise positive reactions to dermal reactivity indicators. Some evidence suggests that loratadine or terfenadine should be discontinued at least 7 days prior to such testing and that the results of such tests should be interpreted with caution even if testing were performed 4-6 weeks after astemizole discontinuance.487

In one study, topical application of an antihistamine (i.e., 2% pyrilamine maleate cream) to the skin test site 10 minutes after antigen testing decreased pruritus but did not suppress wheal or flare 10 minutes after application.318

Acute Toxicity

Manifestations !!navigator!!

Although antihistamines have relatively high therapeutic indexes, overdosage may result in death, especially in infants and children. There have been several reports of toxicity, often occurring within 24-48 hours of repeated topical application of diphenhydramine, in children with pruritus associated with varicella (chickenpox), poison ivy, or sunburn.556,557 Such toxicity included toxic psychosis (sometimes mimicking varicella encephalitis) and occurred in children who received oral and topical diphenhydramine concomitantly.556,557,575,576 The toxicity usually was associated with increased (60-1900 ng/mL) serum concentration of diphenhydramine.556,557 Topical diphenhydramine usually was applied to large areas of the body and usually was contained in Caladryl®, a commercially available lotion containing 1% diphenhydramine and 8% calamine; such combination is no longer commercially available in the US since Caladryl® has been reformulated by the manufacturer to contain pramoxine hydrochloride with calamine or zinc acetate.563 In general, overdosage of diphenhydramine may cause CNS stimulation and/or depression; in young children, CNS stimulation is dominant. Symptoms of antihistamine toxicity in children may resemble atropine overdosage and include fixed dilated pupils, abnormal eye movements, flushed face, dry mouth, urinary retention, fever, excitation, hallucinations, disorientation, delusions, agitation, bizarre behavior, confusion, jitteriness, restlessness, irritability, hyperactivity, delirium, twitching, tiredness, abnormal tongue movement, unsteady gait, trembling extremities, slurred speech, ataxia, incoordination, athetosis, tonic-clonic seizures, and postictal depression. Children recovered gradually from these adverse CNS effects, usually within 24-48 hours following removal of the topical preparation and discontinuance of all diphenhydramine-containing preparations.556,557

Overdosage in adults usually causes CNS depression with drowsiness or coma which may be followed by excitement, seizures, and finally postictal depression. In children and adults, cerebral edema and upper nephron nephrosis, a deepening coma, tachycardia, QRS widening, heart block, cardiorespiratory collapse/arrest,391 cardiogenic shock, and death may occur. The risk of cardiotoxicity has been particularly likely with astemizole and terfenadine;413,417,419,430,433,448,449,459,461,487 however, these 2 antihistamines are no longer commercially available in the US.456,659,660 (See Cautions: Cardiovascular Effects.) Symptoms of overdosage occur within 30 minutes to 2 hours after ingestion; death may occur within 18 hours. Toxic effects may persist for prolonged (e.g., several days) periods after acute overdosage of antihistamines (e.g., astemizole) with long elimination half-lives. Rhabdomyolysis (evidenced by myoglobinuria) has been associated with overdosage of doxylamine.410 Acute toxicity has been reported following topical overdosage of diphenhydramine451,452 or tripelennamine213 (no longer commercially available in the US) in children.

Treatment !!navigator!!

Treatment of acute antihistamine overdosage consists of symptomatic and supportive therapy including artificial respiration, if necessary. If the patient is conscious, has not lost the gag reflex, and is not having seizures, emesis should be induced; however, the manufacturer of trimeprazine (no longer commercially available in the US) stated that emesis should not be induced because dystonic reaction of the head and neck may cause aspiration of gastric contents. The manufacturer of carbinoxamine maleate also states that emesis should not be induced; activated charcoal should be administered and gastric lavage should be considered following ingestion of a potentially life-threatening amount of carbinoxamine maleate.677

While phenothiazine-type antihistamines may exhibit an antiemetic effect, ipecac syrup still may be effective in oral poisonings with these agents if given early (usually within 1 hour) before toxic or antiemetic effects appear. If emesis cannot be induced, gastric lavage and administration of activated charcoal are indicated; an endotracheal tube with cuff inflated should be in place to prevent aspiration of gastric contents. Saline cathartics (e.g., magnesium sulfate) may be administered.

Vasopressor agents, such as norepinephrine or phenylephrine, may be administered if necessary. Epinephrine should not be used, especially with phenothiazine overdosage, because epinephrine may lower the blood pressure further. Analeptic agents should not be used since they may cause seizures. Physostigmine may be useful to counteract the CNS anticholinergic effects of antihistamine intoxication. Diazepam can be given IV in the management of seizures that do not respond to physostigmine. Hyperthermia may be treated with cold packs or sponging with tepid water; sponging with alcohol should not be used.

If hypotension and/or cardiac arrhythmias occur (reported mainly with overdosage of astemizole or terfenadine), appropriate therapy should be instituted.592,593,594 Antiarrhythmic agents that can prolong the QT interval (e.g., class 1A agents) should be avoided in treating overdosage-associated arrhythmias in which prolongation of the QTc interval is a manifestation.416,594,597,600,601 While arrhythmias may resolve spontaneously following discontinuance of the antihistamine,416,420 when necessary, therapy for ventricular tachyarrhythmias with associated QT prolongation (e.g., torsades de pointes) can include temporary atrial or ventricular pacing, IV magnesium sulfate, IV isoproterenol, and/or DC cardioversion (for initial management of sustained, symptomatic runs).416,421,423,600,601,602,603

Pharmacology

Histamine is a physiologically active, endogenous substance (autacoid) that binds to and activates histamine H1- and H2-receptors at various sites in the body.149,150,151,371,389,487 H3-receptors, which may be involved in feedback control of histamine synthesis and release, also have been described.371,372,373,374,375 The principal pharmacologic effects of histamine involve the cardiovascular system, extravascular smooth muscle (e.g., bronchial tree), and exocrine glands (e.g., stimulation of salivary, gastric, lacrimal, and bronchial secretions).149,150,151,371,378,389 Histamine also can stimulate some nerve endings and thus causes pruritus.149 Characteristic cardiovascular effects of histamine include direct and indirect microvascular dilation, hypotension, tachycardia, and flushing (involving H1- and H2-receptors) and increased vascular permeability (thought to principally involve H1-receptors). Intracutaneous injection of histamine produces a “triple response” of local reddening, a bright halo or flare, and wheal formation.149,150,151,371,376 In allergic conditions, histamine and other substances (e.g., leukotrienes, prostaglandins, kinins, serotonin, platelet-activating factor) are secreted from mast cells, basophils, and other cells in response to antigenic stimulation.149,150,152,153,172,371,378 Histamine binds to and activates specific receptors in the nose, eyes, respiratory tract, and skin, causing characteristic allergic signs and symptoms.100,149,150,152,153

The term antihistamine has historically been used to describe drugs that act as H1-receptor antagonists.149,150 Although drugs that antagonize H2-receptors also are commercially available (e.g., cimetidine, famotidine, nizatidine, ranitidine), these drugs generally are not referred to as antihistamines but rather as H2-receptor antagonists.149,150 Antihistamines competitively antagonize most of the smooth muscle stimulating actions of histamine on the H1-receptors of the GI tract, uterus, large blood vessels, and bronchial muscle. Contraction of the sphincter of Oddi and bile duct may be mediated in part by H1-receptors, and opiate-induced contraction of biliary smooth muscle has been antagonized by antihistamines.377 The drugs only are feebly antagonistic to bronchospasm induced by antigen-antibody reactions. Antihistamines also effectively antagonize the action of histamine that results in increased capillary permeability and the formation of edema. H1-receptor antagonists also suppress flare and pruritus that accompany the endogenous release of histamine. Antihistamines appear to act by blocking H1-receptor sites, thereby preventing the action of histamine on the cell; they do not chemically inactivate or physiologically antagonize histamine nor do they prevent the release of histamine. Antihistamines do not block the stimulating effect of histamine on gastric acid secretion, which is mediated by H2-receptors of the parietal cells. For information on the effects of H2-receptor antagonists, see Cimetidine 56:28.12, Famotidine 56:28.12, and Nizatidine 56:28.12.

The basic ethylamine group common to antihistamines also is common to anticholinergics, ganglionic and adrenergic blocking agents, local anesthetics, and antispasmodics; antihistamines therefore may be expected to exhibit some of the activities of these other classes of drugs. Some antihistamines also demonstrate a quinidine-like effect on myocardial conduction, and they may enhance the pressor action of norepinephrine. The antiemetic and antimotion-sickness actions of some antihistamines appear to result, at least in part, from their central anticholinergic and CNS depressant properties. The effects of diphenhydramine on parkinsonian syndrome and drug-induced extrapyramidal reactions are also apparently related to its central anticholinergic effects.

Although the antipruritic effect of systemically administered or locally applied antihistamines in conditions associated with histamine-induced pruritus appears to result from a peripheral antihistaminic effect and possibly a local anesthetic effect,149,171,349 the sedative effect of systemically administered antihistamines also appears to contribute to their antipruritic activity.11,171 The drugs are more effective antipruritics when administered systemically than when applied topically, especially when pruritus is generalized.349 Because pruritus can involve mediators other than histamine, the antipruritic efficacy of antihistamines is not routine.349

Pharmacokinetics

Limited information is available on the pharmacokinetics of most antihistamines.

Absorption !!navigator!!

Antihistamines generally are well absorbed following oral or parenteral administration, but various salts may differ in activity and toxicity because of differences in solubility or absorption. The least soluble antihistamines are often the least toxic and may have a slow onset but prolonged duration of action. Following oral administration of antihistamines, symptomatic relief of allergic reactions usually begins within 15-30 minutes and usually is maximal within 1 hour. The duration of action is variable but symptoms usually are relieved for 3-6 hours after oral administration of most antihistamines. There may be some decrease in effectiveness with prolonged use of these drugs, although a substantial degree of tolerance to the antihistaminic effects generally does not occur. However, tolerance to the sedative effects may occur.

Some antihistamines (e.g., astemizole [no longer commercially available in the US], cetirizine, desloratadine, loratadine) exhibit a slower onset of action and/or prolonged duration of effect. Following single- and multiple-dose administration, the long-acting antihistamine loratadine exhibits antihistaminic effects beginning within 1-3 hours, reaching a maximum at 8-10 hours, and lasting in excess of 24 hours.470 Following single- and multiple-dose administration of a 5-mg dose of desloratadine, the antihistaminic effect of the drug is apparent within 1 hour and lasts for 24 hours.670 Following oral administration of a single 10-mg dose of cetirizine hydrochloride in healthy individuals, the antihistaminic effect of the drug is apparent within 20-60 minutes and lasts for at least 24 hours.509 Following oral administration of a 5-mg dose of levocetirizine dihydrochloride in patients with allergic rhinitis, the antihistaminic effect of the drug is apparent within 1 hour and lasts for at least 24 hours. 685

Topically applied antihistamines generally do not readily penetrate intact skin, especially when salts of the drugs are used.349 However, percutaneous absorption can occur,213,214,215,319,349,556 especially when the stratum corneum is disrupted,349,556 and rarely may result in systemic effects and toxicity.44,319,349,356,556

Distribution !!navigator!!

The distribution of most antihistamines has not been fully characterized. Those compounds that have been studied show highest concentrations in the lungs and lower concentrations in spleen, kidneys, brain, muscle, and skin. Protein binding of these agents ranges from 50-99%.

Unlike other currently available antihistamines, second generation (also referred to as relatively “nonsedating”) antihistamines such as acrivastine, astemizole, cetirizine, desloratadine, fexofenadine, levocetirizine, loratadine, and terfenadine (no longer commercially available in the US) appear to distribute poorly or not appreciably into the CNS at usual dosages.154,155,156,157,158,159,160,161,162,163,164,165,166,167,404,405,406,470,471,472,473,474,487,495,496,497,498,516,669,670,695 It is thought that this lack of CNS distribution results principally from the inability of these agents to cross the tightly fused outer membranes of endothelial cells lining the brain capillaries.487,498 Cetirizine, because of its substantial polarity, also does not readily cross the blood-brain barrier;509,583,584 however, some data indicate that the drug may cause more somnolence than other second generation antihistamines.583 Levocetirizine also is considered mildly sedating.695

Small amounts of the drugs appear to be distributed into milk.

Elimination !!navigator!!

The metabolic fate of most antihistamines is not clearly established. The drugs usually appear to be extensively metabolized, mainly in the liver. Some second generation antihistamines (e.g., astemizole, loratadine, terfenadine) are metabolized principally by the cytochrome P-450 microsomal enzyme system, mainly by the isoenzyme 3A4 (CYP3A4), although other isoenzymes, including CYP1A2 and CYP2D6, also may be involved.156,157,161,477,512,587,588,589,590,591,594,596,597,607,635,650,651,652,653,654 Desloratadine also is extensively metabolized; however, the enzyme(s) responsible for metabolism of the drug has not been identified.670 Other second generation antihistamines (e.g., cetirizine, fexofenadine, levocetirizine) appear to be only minimally metabolized in the liver.509,575,576,648,685

Metabolism of some antihistamines that are extensively metabolized in the liver (e.g., astemizole, terfenadine) may be substantially reduced in patients with hepatic impairment and possibly in geriatric patients.413,417,418,419,422,424,433,447,448,449,456,459,466,476,512 In addition, metabolism also may be substantially reduced in patients concomitantly receiving foods (e.g., grapefruit juice)512,541,542,543,544,555,596,607,616,617 or drugs (e.g., certain azole-derivative anti-infective agents, including fluconazole, itraconazole, ketoconazole, metronidazole, and miconazole; certain macrolide antibiotics, including clarithromycin, erythromycin, and troleandomycin; mibefradil [no longer commercially available in the US]; possibly certain human immunodeficiency virus [HIV] protease inhibitors, including indinavir, nelfinavir, ritonavir, and saquinavir; possibly some serotonin-reuptake inhibitors, including fluoxetine, fluvoxamine, nefazodone, paroxetine, and sertraline; zileuton; quinine) that affect the hepatic microsomal enzyme system.418,419,420,443,444,445,446,455,475,476,477,478,512,547,548,549,554,574,594,596,597,598,605,606,607,615,639 Decreased metabolism may result in accumulation of potentially toxic concentrations of the unchanged antihistamines that may be associated with serious adverse cardiac effects.418,419,422,443,447,448,449,476,512,594,596,597,607 (See Cautions: Cardiovascular Effects and see Drug Interactions.)

Many antihistamines are excreted in urine as inactive metabolites within 24 hours; however, some antihistamines (e.g., terfenadine, desloratadine, loratadine, astemizole, acrivastine) have active H1-antagonist metabolites. Negligible amounts of most antihistamines are excreted unchanged in urine; however, cetirizine and levocetirizine are excreted in urine mainly as unchanged drug.577,578,579,583,685,686

Chemistry

Antihistamines (histamine H1-receptor antagonists) competitively inhibit most of the pharmacologic actions of histamine.

Antihistamines have been classified chemically and also have been classified according to their propensity to cause sedation, with relatively sedating antihistamines (i.e., conventional, prototypical antihistamines) being classified as first generation and relatively “nonsedating” antihistamines (e.g., acrivastine, astemizole [no longer commercially available in the US], desloratadine, fexofenadine, loratadine, terfenadine [no longer commercially available in the US]) being classified as second generation.435,471,487,495,496,497,498,516 Cetirizine also is considered a second generation antihistamine; however, some data indicate that it causes more sedation than other second generation antihistamines.583 Levocetirizine, the active R enantiomer of cetirizine, is considered a mildly sedating antihistamine695 and has been found to be slightly more sedating than desloratadine.687

FIRST GENERATION ANTIHISTAMINES

azatadine*

diphenhydramine

brompheniramine

doxylamine

carbinoxamine

hydroxyzine

chlorpheniramine

meclizine

clemastine

promethazine

cyproheptadine

triprolidine

dimenhydrinate

SECOND GENERATION ANTIHISTAMINES

acrivastine

fexofenadine

astemizolea

levocetirizine

cetirizine

loratadine

desloratadine

terfenadinea

ano longer commercially available in the US

Most antihistamines are substituted ethylamines. In general, these molecules consist of 3 portions: R1 = nucleus, X = a linkage such as nitrogen, oxygen, or carbon, and the ethylamine group. Antihistamines can be depicted by a general formula:

R1 is composed of aromatic and/or heterocyclic groups, which may be separated from X by a methylene group. Hydrogenation of the rings in the R1 portion of the molecule decreases antihistamine activity. Usually, activity of an antihistamine is increased by substitution of a halogen atom in the para position of the phenyl or benzyl group of R1. For maximum activity, the terminal nitrogen of the ethylamine group should be a tertiary amine with methyl groups or a small cyclic moiety in R2 and R3. In optically active compounds, the dextro isomer (e.g., dexchlorpheniramine, dexbrompheniramine) usually is more active than the levo isomer.

Antihistamines can be classified on the basis of X substitution as follows:

ETHYLENEDIAMINE DERIVATIVES

antazoline

pyrilamine

methapyrilene

tripelennamine

This group of antihistamines has nitrogen in the X position. Ethylenediamine derivatives have relatively weak CNS effects; however, drowsiness may occur in some patients. Adverse GI effects are common with this group of antihistamines.

ETHANOLAMINE DERIVATIVES (AMINOALKYL ETHERS)

bromodiphenhydramine*

diphenhydramine

carbinoxamine

diphenylpyraline

clemastine

doxylamine

dimenhydrinate

phenyltoloxamine

This group of antihistamines, which has oxygen in the X position, has substantial atropine-like activity. Drugs in this group commonly cause CNS depression; with usual doses, drowsiness occurs in about 50% of patients who receive ethanolamine derivative antihistamines. The incidence of adverse GI effects with these antihistamines is relatively low. Dimenhydrinate (see 56:22.08) and diphenhydramine also are used as antiemetics.

ALKYLAMINES (PROPYLAMINE DERIVATIVES)

acrivastine

dimethindene

brompheniramine

pheniramine

chlorpheniramine

pyrrobutamine

dexbrompheniramine

triprolidine

dexchlorpheniramine

These antihistamines contain a carbon atom in the X position. Alkylamines cause less drowsiness and more CNS stimulation than the other antihistamines and thus are suitable for daytime use.

PHENOTHIAZINE DERIVATIVES

promethazine

In this group of antihistamines, nitrogen, as part of a phenothiazine nucleus, is in the X position. Most phenothiazines are used principally as antipsychotics (see 28:16.08); however, some are useful as antihistamines, antipruritics, and antiemetics.

PIPERAZINE DERIVATIVES

cetirizine

levocetirizine

hydroxyzine

meclizine

In this group, nitrogen, as part of a piperazine nucleus, is in the X position. Meclizine is used in the treatment of motion sickness. (See 56:22.08.) Hydroxyzine is used as a tranquilizer, sedative, antipruritic, and antiemetic. (See 28:24.92.)

OTHERS

astemizolea

fexofenadine

azatadinea

loratadine

cyproheptadine

phenindamine

desloratadine

terfenadinea

ano longer commercially available in the US

Copyright

AHFS® Drug Information. © Copyright, 1959-2024, Selected Revisions September 24, 2018. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, MD 20814.

References

Only references cited for selected revisions after 1984 are available electronically.

11. Anon. Choice of antihistamines. Med Lett Drugs Ther . 1971; 13:102-4. [PubMed 4150398]

44. Bleumink E. Antihistamines. In: Dukes MNG, ed. Meyler's side effects of drugs. Vol 8. New York: Excerpta Medica; 1975:406-17.

50. Fisher AA. Antihistamine dermatitis. Cutis . 1976; 18:329,330,336. [PubMed 138569]

100. Food and Drug Administration. Over-the-counter drugs: establishment of a monograph for OTC cold, cough, allergy, bronchodilator and antiasthmatic products. [21 CFR 341] Fed Regist . 1976; 41:38312-424. (Cited in previous revisions as reference #16.) (IDIS 66640)

101. Key Pharmaceuticals. Trinalin®(azatadine maleate and pseudoephedrine sulfate) Repetabs® prescribing information (dated 1996 Jun). In: Physicians' desk reference. 52nd ed. Montvale, NJ: Medical Economics Company Inc; 1998:1339-40.

102. Lin C, Lim J, Scymchowicz S. Bioavailability of d-pseudoephedrine and azatadine from a repeat action tablet formulation. J Int Med Res . 1982; 10:122-5. [PubMed 7067923]

103. Schering Corporation. Optimine® prescribing information. In: Huff BB, ed. Physicians' desk reference. 38th ed. Oradell, NJ: Medical Economics Company Inc; 1984:1795-7.

104. The United States pharmacopeia, 20th rev, and The national formulary, 15th ed. Suppl 3. Rockville, MD: The United States Pharmacopeial Convention, Inc; 1982:46.

105. Falliers CJ, Redding MA. Controlled comparison of a new antihistamine-decongestant combination to its individual components. Ann Allergy . 1980; 45:75-80. [PubMed 6157338]

106. Zubizaretta J. Azatadine maleate/pseudoephedrine sulfate repetabs versus placebo in the treatment of severe perennial allergic rhinitis. J Int Med Res . 1980; 8:395-9. [PubMed 6108263]

107. Tarasido JC. Azatadine maleate/pseudoephedrine sulfate repetabs versus placebo in the treatment of severe seasonal allergic rhinitis. J Int Med Res . 1980; 8:391-4. [PubMed 6108262]

108. Connell JT. A novel method to assess antihistamine and decongestant efficacy. Ann Allergy . 1979; 42:278-85. [PubMed 88194]

109. Simons FER, Frith EM, Simons KJ. The pharmacokinetics and antihistaminic effects of brompheniramine. J Allergy Clin Immunol . 1982; 70:458-64. [PubMed 6128358]

110. Bruce RB, Turnbull LB, Newman JH et al. Metabolism of brompheniramine. J Med Chem . 1968; 11:1031-4. [PubMed 4386938]

111. Kabasakalian P, Taggart M, Townley E. Urinary excretion of pheniramine and its N -demethylated metabolites in man—comparison with chlorpheniramine and brompheniramine data. J Pharm Sci . 1968; 57:621-3. [PubMed 4385103]

112. Hanna S, Tang A. GLC determination of chlorpheniramine in human plasma. J Pharm Sci . 1974; 63:1954-7. [PubMed 4449031]

113. Peets EA, Jackson M, Symchowicz S. Metabolism of chlorpheniramine maleate in man. J Pharmacol Exp Ther . 1972; 180:464-74.

114. Kotzan JA, Vallner JJ, Stewart JT et al. Bioavailability of regular and controlled-release chlorpheniramine products. J Pharm Sci . 1982; 71:919-23. [PubMed 7120098]

115. Simons FER, Luciuk GH, Simons KJ. Pharmacokinetics and efficacy of chlorpheniramine in children. J Allergy Clin Immunol . 1982; 69:376-81. [PubMed 7069073]

116. Thompson JA, Bloedow DC, Leffert FH. Pharmacokinetics of intravenous chlorpheniramine in children. J Pharm Sci . 1981; 70:1284-6. [PubMed 7299679]

117. Vallner JJ, Needham TE, Chan W et al. Intravenous administration of chlorpheniramine to seven subjects. Curr Ther Res . 1979; 26:449-53.

118. Chiou WL, Athanikar NK, Huang SM. Long half-life of chlorpheniramine. N Engl J Med . 1979; 300:501. [PubMed 759945]

119. Lange WE, Theodore JM, Pruyn FJ. In vivo determination of certain aralkylamines. J Pharm Sci . 1968; 57:124-7. [PubMed 5652111]

120. Kabasakalian P, Taggart M, Townley E. Urinary excretion of pheniramine and its N -demethylated metabolites-comparison with chlorpheniramine and brompheniramine data. J Pharm Sci . 1968; 57:621-3. [PubMed 4385103]

121. Kabasakalian P, Taggart M, Townley E. Urinary excretion of chlorpheniramine and its N -demethylated metabolites in man. J Pharm Sci . 1968; 57:856-8. [PubMed 5657548]

122. Huang SM, Athanikar NK, Sridhar K et al. Pharmacokinetics of chlorpheniramine after intravenous and oral administration in normal adults. Eur J Clin Pharmacol . 1982; 22:359-65. [PubMed 7106172]

123. Huang SM, Huang YC, Chiou WL. Oral absorption and presystemic first-pass effect of chlorpheniramine in rabbits. J Pharmacokinet Biopharm . 1981; 9:725-38. [PubMed 7341757]

124. Huang SM, Chiou WL. Pharmacokinetics and tissue distribution of chlorpheniramine in rabbits after intravenous administration. J Pharmacokinet Biopharm . 1981; 9:711-23. [PubMed 7341756]

125. Athanikar NK, Peng GW, Nation RL et al. Chlorpheniramine. I. Rapid quantitative analysis of chlorpheniramine in plasma, saliva and urine by high-performance liquid chromatography. J Chromatogr . 1979; 162:367-76. [PubMed 528601]

126. Dube LM, Bloch R, Warner RN et al. Pharmacokinetics of chlorpheniramine maleate in chronic renal failure: effect of hemodialysis and peritoneal dialysis. In: Official Program and Abstracts of Papers presented before the APhA Academy of Pharmaceutical Sciences. 1980; 10:84. Abstract.

127. Beckett AH, Wilkinson GR. Influence of urine pH and flow rate on the renal excretion of chlorpheniramine in man. J Pharm Pharmacol . 1965; 17:256-7. [PubMed 14327721]

128. Lai CM, Stoll RG, Look ZM et al. Urinary excretion of chlorpheniramine and pseudoephedrine in humans. J Pharm Sci . 1979; 68:1243-6. [PubMed 41928]

129. West S, Brandon B, Stolley P et al. A review of antihistamines and the common cold. Pediatrics . 1975; 56:100-7. [PubMed 240145]

130. Howard JC Jr, Kantner TR, Lilienfield LS et al. Effectiveness of antihistamines in the symptomatic management of the common cold. JAMA . 1979; 242:2414-7. [PubMed 490852]

131. Albert KS, Hallmark MR, Sakmar E et al. Pharmacokinetics of diphenhydramine in man. J Pharmacokinet Biopharm . 1975; 3:159-70. [PubMed 1159620]

132. Carruthers SG, Shoeman DW, Hignite CE et al. Correlations between plasma diphenhydramine level and sedative and antihistamine effects. Clin Pharmacol Ther . 1978; 23:375-82. [PubMed 24512]

133. Glazko AJ, Dill WA, Young RM et al. Metabolic disposition of diphenhydramine. Clin Pharmacol Ther . 1974; 16:1066-76. [PubMed 4447663]

134. Bilzer W, Gundert-Remy U, Weber E. Relationship between antihistaminic activity and plasma level of diphenhydramine. Eur J Clin Pharmacol . 1974; 7:393-5. [PubMed 4154042]

135. Glazko AJ, Dill WA. Biochemical studies on diphenhydramine (Benadryl®). II. Distribution in tissues and urinary excretion. J Biol Chem . 1949; 179:403-8. [PubMed 18119256]

136. Parkin DE. Probably Benadryl withdrawal manifestations in a newborn infant. J Pediatr . 1974; 85:580. [PubMed 4443870]

137. O'Brien TE. Excretion of drugs in human milk. Am J Hosp Pharm . 1974; 31:844-54. [PubMed 4608122]

138. Knowles JA. Excretion of drugs in milk: a review. J Pediatr . 1965; 66:1068-82. [PubMed 14288461]

139. Chang T, Okerholm RA, Glazko AJ. Identification of diphenhydramine (Benadryl®) metabolites in human subjects. Res Commun Chem Pathol Pharmacol . 1974; 9:391-404. [PubMed 4445562]

140. Russo RM, Gururaj VJ, Allen JE. The effectiveness of diphenhydramine HCl in pediatric sleep disorders. J Clin Pharmacol . 1976; 16:284-8. [PubMed 770511]

141. Food and Drug Administration. Drug efficacy study implementation; revocation of the exemption category for oral prescription drugs for cough, cold, or allergy (“paragaph XIV/category 15”); followup notice and opportunity for hearing. Docket No. 83N-0005; [DESI No. 11935] Fed Regist . 1983; 48:56854-6.

142. Schering Corporation. Disophrol® Chronotab® prescribing information. In: Huff BB, ed. Physicians' desk reference. 36th ed. Oradell, NJ: Medical Economics Company Inc; 1982:1701.

143. Schering Corporation. Drixoral®sustained-action tablets prescribing information. In: Huff BB, ed. Physicians' desk reference. 36th ed. Oradell, NJ: Medical Economics Company Inc.; 1982:1703-4.

144. Schering Corporation. Disophrol® tablets prescribing information. In: Huff BB, ed. Physicians' desk reference. 33rd ed. Oradell, NJ: Medical Economics Company Inc; 1979:1527-8.

145. Schering Corporation. Disophrol® Chronotab® patient information. In: Huff BB, ed. Physicians' desk reference for nonprescription drugs. 6th ed. Oradell, NJ: Medical Economics Company Inc; 1985:677-8.

146. Schering Corporation. Drixoral® sustained-action tablets patient information. In: Huff BB, ed. Physicians' desk reference for nonprescription drugs. 6th ed. Oradell, NJ: Medical Economics Company Inc; 1985:678.

147. Lederle Laboratories. Dexbrompheniramine maleate USP and pseudoephedrine sulfate USP Sequels®. Pearl River, NY; 1982 Jul.

148. Schering Corporation. Disophrol® tablets patient information. Kenilworth, NJ. Undated.

149. Douglas WW. Histamine and 5-hydroxytryptamine (serotonin) and their antagonists. In: Gilman AG, Goodman LS, Rall TW et al, eds. Goodman and Gilman's the pharmacological basis of therapeutics. 7th ed. New York: Macmillan Publishing Company; 1985:605-38.

150. Local hormones and autacoids: biogenic amines, purines, kinins, and prostaglandins. In: Bowman WC, Rand MJ, eds. Textbook of pharmacology. 2nd ed. Oxford: Blackwell Scientific Publications; 1980:12.1-12.41.

151. Cirillo VJ, Tempero KF. The pharmacology and therapeutic use of H1 and H2 antihistamines. In: Miller RR, Greenblatt DJ, eds. Drug therapy reviews. Vol 2. New York: Elsevier/North Holland Inc; 1979:24-47.

152. Hypersensitivity reactions. In: Bauman WC, Rand MJ, eds. Textbook of Pharmacology. 2nd ed. Oxford: Blackwell Scientific Publications; 1980:13.23-13.28.

153. Immune mechanisms in tissue damage. In: Stites DP, Stobo JD, Fudenberg HH et al, eds. Basic clinical immunology. 4th ed. Los Altos, CA: Lange Medical Publications; 1982:136-55.

154. Woodward JK, Munro NL. Terfenadine, the first non-sedating antihistamine. Arzneimittelforschung . 1982; 32:1154-6. [PubMed 6129860]

155. Merrell Dow Pharmaceuticals Inc. Seldane® prescribing information. Cincinnati, OH; 1985 May.

156. Merrell Dow Pharmaceuticals Inc. Seldane® (terfenadine) monograph. Cincinnati, OH; 1985.

157. Merrell Dow Pharmaceuticals Inc. Product information form for American Hospital Formulary Service on Seldane®. Cincinnati, OH; 1985 Apr 1.

158. Kinsolving CR, Munro NL, Carr AA. Separation of the CNS and H1-receptor effects of antihistamine agents. Pharmacologist . 1973; 15:221.

159. Cheng HC, Woodward JK. Antihistaminic effect of terfenadine: a new piperidine-type antihistamine. Drug Dev Res . 1982; 2:181-96.

160. Cheng HC, Woodward JK. A kinetic study of the antihistaminic effect of terfenadine. Arzneimittelforschung . 1982; 32:1160-6. [PubMed 6129862]

161. Sorkin EM, Heel RC. Terfenadine: a review of its pharmacodynamic properties and therapeutic efficacy. Drugs . 1985; 29:34-56. [PubMed 2857636]

162. Koch H. Terfenadine: specific peripheral H1-histamine receptor antagonist. Pharm Int . 1983; 4:252-3.

163. Weich NL, Martin JS. Absence of an effect of terfenadine on guinea pig brain histamine H1-receptors in vivo determined by receptor binding techniques. Arzneimittelforschung . 1982; 32:1167-70. [PubMed 6817763]

164. Rose C, Quach TT, Llorens C et al. Relationship between occupation of cerebral H1-receptors and sedative properties of antihistamines: assessment in the case of terfenadine. Arzneimittelforschung . 1982; 32:1171-3. [PubMed 6129863]

165. Nicholson AN. Antihistamines and sedation. Lancet . 1983; 2:211-2. [PubMed 6135040]

166. Norman PS. New developments in treating allergic rhinitis. Drug Ther . 1984; 14:117,126,127,130-2.

167. Leeson GA, Chan KY, Knapp WC et al. Metabolic disposition of terfenadine in laboratory animals. Arzneimittelforschung . 1982; 32:1173-8. [PubMed 6817764]

168. AMA Division of Drugs. AMA drug evaluations. 5th ed. Chicago: American Medical Association; 1983:1465-79.

169. Food and Drug Administration. Cold, cough, allergy, bronchodilator, and antiasthmatic drug products for over-the-counter human use; tentative final monograph for OTC antihistamine drug products. [21 CFR Part 341] Fed Regist . 1985; 50:2200-18. (IDIS 195256)

170. Anon. Treatment of seasonal and perennial rhinitis. BMJ . 1981; 283:808-10. [PubMedCentral][PubMed 6117350]

171. Krause L, Shuster S. Mechanism of action of antipruritic drugs. BMJ . 1983; 287:1199-200. [PubMedCentral][PubMed 6138120]

172. Naclerio RM, Proud D, Togia AG et al. Inflammatory mediators in late antigen-induced rhinitis. N Engl J Med . 1985; 313:65-70. [PubMed 2582257]

173. Deutsch PH. Dermatographism treated with hydroxyzine and cimetidine and ranitidine. Ann Intern Med . 1984; 101:569. [PubMed 6089638]

174. Cook J, Shuster S. The effect of H1 and H2receptor antagonists on the dermographic response. Acta Derm Venereol . 1983; 63:260-2. [PubMed 6192650]

175. Cook LJ, Shuster S. Lack of effect of cimetidine in chronic-idiopathic urticaria. Acta Derm Venereol . 1983; 63:265-7. [PubMed 6192652]

176. Singh G. H2 blockers in chronic urticaria. Int J Dermatol . 1984; 23:627-8. [PubMed 6151554]

177. Harvey RP, Wegs J, Schocket AL. A controlled trial of therapy in chronic urticaria. J Allergy Clin Immunol . 1981; 68:262-6. [PubMed 6116728]

178. Harvey RP, Schocket AL. The effect of H1 and H2 blockade on cutaneous histamine response in man. J Allergy Clin Immunol . 1980; 65:136-9. [PubMed 6101337]

179. Monroe EW, Cohen SH, Kalbfleisch J et al. Combined H1 and H2 antihistamine therapy in chronic urticaria. Arch Dermatol . 1981; 117:404-7. [PubMed 6114712]

180. Nicholson AN, Stone BM. Performance studies with the H1-histamine receptor antagonists, astemizole and terfenadine. Br J Clin Pharmacol . 1982; 13:199-202. [PubMedCentral][PubMed 6120713]

181. Nicholson AN, Smith PA, Spencer MB. Antihistamines and visual function: studies on dynamic acuity and the pupillary response to light. Br J Clin Pharmacol . 1982; 14:683-90. [PubMedCentral][PubMed 6128019]

182. Luscombe DK, Nicholls PJ, Parish PA. Comparison of the effects of azatadine and terfenadine on human performance. Pharmatherapeutica . 1983; 3:370-5. [PubMed 6137832]

183. Fink M, Irwin P. CNS effects of the antihistamines diphenhydramine and terfenadine (RMI 9918). Pharmakopsychiatr Neuro Psychopharmakol . 1979; 12:35-44.

184. Clarke CH, Nicholson AN. Performance studies with antihistamines. Br J Clin Pharmacol . 1978; 6:31-5. [PubMedCentral][PubMed 27204]

185. Brandon ML, Weiner M. Clinical studies of terfenadine in seasonal allergic rhinitis. Arzneimittelforschung . 1982; 32:1204-5. [PubMed 6129869]

186. Dugue P, Birnbaum J, Poisson A et al. Clinical studies with terfenadine in seasonal allergic rhinitis in France. Arzneimittelforschung . 1982; 32:1206-8. [PubMed 6129870]

187. Melillo G, D'Amato G, Zanussi C et al. A multicentre controlled trial of terfenadine, dexchlorpheniramine, and placebo in allergic rhinitis. Arzneimittelforschung . 1982; 32:1202-3. [PubMed 6129868]

188. Weiner M. Sedation and antihistaminics. Arzneimittelforschung . 1982; 32:1193-5. [PubMed 6129866]

189. Barlow JLR, Beitman RE, Tsai TH. Terfenadine, safety and tolerance in controlled clinical trials. Arzneimittelforschung . 1982; 32:1215-7. [PubMed 6129874]

190. Howarth PH, Holgate ST. Comparative trial of two non-sedative H1 antihistamines, terfenadine and astemizole, for hay fever. Thorax . 1984; 39:688-72.

191. Nicholson AN. Antihistaminic activity and central effects of terfenadine. Arzneimittelforschung . 1982; 32:1191-3. [PubMed 6129865]

192. Moser L, Huther KJ, Koch-Weser J et al. Effects of terfenadine and diphenhydramine alone or in combination with diazepam or alcohol on psychomotor performance and subjective feelings. Eur J Clin Pharmacol . 1978; 14:417-23. [PubMed 33053]

193. Parke-Davis. Benadryl® (diphenhydramine hydrochloride capsules) prescribing information. In: Physicians' desk reference. 46th ed. Montvale NJ: Medical Economics Company Inc; 1992:1691-2.

194. Parke-Davis. Benylin® cough syrup patient information. In: Huff BB, ed. Physicians' desk reference. 39th ed. Oradell, NJ: Medical Economics Company Inc; 1985:1486.

195. Forest Pharmaceuticals. Ambenyl® cough syrup prescribing information. In: Physicians' desk reference. 45th ed. Oradell, NJ: Medical Economics Company Inc; 1991:972-3.

196. Food and Drug Administration. External analgesic drug products for over-the-counter human use; tentative final monograph. [21 CFR Part 348] Fed Regist . 1983; 48:5852-69.

197. Food and Drug Administration. Over-the-counter nighttime sleep-aid and stimulant products; tentative final orders. [21 CFR Parts 338,340] Fed Regist . 1978; 114:25544-602.

198. Greenberger P, Patterson R. Safety of therapy for allergic symptoms during pregnancy. Ann Intern Med . 1978; 89:234-7. [PubMed 28058]

199. Saxén I. Cleft palate and maternal diphenhydramine intake. Lancet . 1974; 1:407-8. [PubMed 4131054]

200. Iuliucci JD, Gautieri RF. Morphine-induced malformations. II: Influence of histamine and diphenhydramine. J Pharm Sci . 1971; 60:420-5. [PubMed 4398382]

201. Smith Kline & French. Temaril® prescribing information. In: Huff BB, ed. Physicians' desk reference. 39th ed. Oradell, NJ: Medical Economics Company Inc; 1985:1976-7.

202. Kahn A, Blum D. Possible role of phenothiazines in sudden infant death. Lancet . 1979; 2:364-5. [PubMed 89428]

203. Kahn A, Blum D. Phenothiazines and sudden infant death syndrome. Pediatrics . 1982; 70:75-8. [PubMed 7088637]

204. Stanton AN. Sudden infant death syndrome and phenothiazines. Pediatrics . 1983; 71:986-7. [PubMed 6856418]

205. Kahn A, Blum D. Sudden infant death syndrome and phenothiazines. Pediatrics . 1983; 71:987-8.

206. Mann NP. Trimeprazine and respiratory depression. Arch Dis Child . 1981; 56:481-2. [PubMedCentral][PubMed 7259282]

207. Kahn A, Hasaerts D, Blum D. Phenothiazine-induced sleep apnea in normal infants. Pediatrics . 1985; 75:844-7. [PubMed 3991270]

208. Rao GS, Krishna G, Gillette JR. Metabolism, tissue distribution and covalent binding of tripelennamine and its N -nitroso derivative in the rat. J Pharmacol Exp Ther . 1975; 195:433-40. [PubMed 1195130]

209. Schaffer MI, Lin RL, Wu Chen NB et al. Spontaneous live birth with a maternal history of intravenous use of pentazocine and tripelennamine (T's and blues). J Forensic Sci . 1983; 28:489-95. [PubMed 6683302]

210. Luders RC, Williams J, Fried K et al. Determination of pyribenzamine (tripelennamine) residues in bovine milk. J Agric Food Chem . 1970; 18:1153-5. [PubMed 5483055]

211. Chaudhuri NK, Servando OA, Manniello MJ et al. Metabolism of tripelennamine in man. Drug Metab Dispos . 1976; 4:372-8. [PubMed 8293]

212. Weinman EO, Geissman TA. The distribution, excretion and metabolism of14C-labeled tripelennamine (pyribenzamine) by guinea pigs. J Pharmacol Exp Ther . 1959; 125:1-13. [PubMed 13621384]

213. Schipior PG. An unusual case of antihistamine intoxication. J Pediatr . 1967; 71:589-91. [PubMed 4227701]

214. Peck SM, Finkle B, Mayer GS et al. Effects of various modes of administration of pyribenzamine on the histamine wheal and epidermal sensitivity reactions. J Invest Dermatol . 1950; 14:177.

215. LeVan P, Sternberg TH, Perry DJ. Studies of the “antihistaminic” effect of pyribenzamine administered by various routes. Calif Med . 1951; 74:256-9. [PubMedCentral][PubMed 14821823]

216. Reid RW, Gerbeck CM. Detection of pentazocine and tripelennamine in urine. Clin Chem . 1981; 27:10-13. [PubMed 7449089]

217. Bayley M, Walsh FM, Valske MJ. Report of a fatal, acute tripelennamine intoxication. J Forensic Sci . 1975; 20:539-43. [PubMed 1151312]

218. McGavack TH, Drekter IJ, Schutzer S et al. Levels for pyribenzamine and Benadryl in blood and urine following a single orally administered dose. J Allergy . 1948; 19:251-5. [PubMed 18871142]

219. Darling CM. Histamine and antihistaminic agents. In: Doerge RF, ed. Wilson and Gisvold's textbook of organic medicinal and pharmaceutical chemistry. 8th ed. Philadelphia: JB Lippincott Company; 1982:583-606.

220. Monforte JR, Gault R, Smialek J et al. Toxicological and pathological findings in fatalities involving pentazocine and tripelennamine. J Forensic Sci . 1983; 28:90-101. [PubMed 6680755]

221. Chasnoff IJ, Burns WJ, Schnoll SH. Perinatal addiction: the effects of maternal narcotic and nonnarcotic substance abuse on the fetus and neonate. NIDA Res Monogr Ser . 1984; 49:220-6.

222. Dunn DW, Reynolds J. Neonatal withdrawal symptoms associated with “T's and blues” (pentazocine and tripelennamine). Am J Dis Child . 1982; 136:644-5. [PubMed 7091098]

223. Chasnoff IJ, Hatcher R, Burns WJ et al. Pentazocine and tripelennamine (T's and blues): effects on the fetus and neonate. Dev Pharmacol Ther . 1983; 6:162-9. [PubMed 6861602]

224. Anon. Pentazocine abuse rises—schedule IV status proposed. FDA Drug Bull . 1978; 8:34.

225. Lahmeyer HW, Steingold RG. Pentazocine and tripelennamine: a drug abuse epidemic? Int J Addict . 1980; 15:1219-32.

226. Showalter CV. T's and blues: abuse of pentazocine and tripelennamine. JAMA . 1980; 224:1224-5.

227. Poklis A. Pentazocine/tripelennamine (T's and blues) abuse: a five year survey of St. Louis, Missouri. Drug Alcohol Depend . 1982; 10:257-67. [PubMed 7166138]

228. De Bard ML, Jagger JA. T's and B's—midwestern heroin substitute. Clin Toxicol . 1981; 18:1117-23. [PubMed 7318393]

229. Itkonen J, Schnoll S, Daghestani A et al. Accelerated development of pulmonary complications due to illicit intravenous use of pentazocine and tripelennamine. Am J Med . 1984; 76:617-22. [PubMed 6711575]

230. Butch AJ, Yokel RA, Sigell LT et al. Abuse and pulmonary complications of injecting pentazocine and tripelennamine tablets. Clin Toxicol . 1979; 14:301-6. [PubMed 455920]

231. Lahmeyer HW, Steingold RG. Medical and psychiatric complications of pentazocine and tripelennamine abuse. J Clin Psychiatry . 1980; 41:275-8. [PubMed 7400105]

232. Caplan LR, Thomas C, Banks G. Central nervous system complications of addiction to T's and blues. Neurology . 1982; 32:623-8. [PubMed 7201092]

233. Poklis A, Mackell MA. Pentazocine and tripelennamine (T's and blues) abuse: toxicological findings in 39 cases. J Anal Toxicol . 1982; 6:110-4.

234. Heaney RM, Gotlieb N. Granulocytopenia after intravenous abuse of pentazocine and tripelennamine (“Ts and blues”). South Med J . 1983; 76:654-6. [PubMed 6844971]

235. Reinhart S, Barrett SM. An acute hypertensive response after intravenous use of a new pentazocine formulation. Ann Emerg Med . 1985; 14:591-3. [PubMed 3994086]

236. Burton JF, Zawadzki S, Wetherell HR et al. Mainliners and blue velvet. J Forensic Sci . 1965; 10:466-72. [PubMed 5839798]

237. Zwed JJ. Pulmonary angiothrombosis caused by “blue velvet” addiction. Ann Intern Med . 1970; 73:771-4. [PubMed 5476210]

238. Lerner AM, Oerther FJ. Characteristics and sequelae of paregoric abuse. Ann Intern Med . 1966; 65:1019-30. [PubMed 5923084]

239. Wendt VE, Puro HE, Shapira J et al. Angiothrombotic pulmonary hypertension in addicts: “blue velvet” addiction. JAMA . 1964; 188:755-7. [PubMed 14122687]

240. O'Driscoll WG, Lindley GR. Self-administration of tripelennamine by a narcotic addict. N Engl J Med . 1957; 257:376-7. [PubMed 13464943]

241. Houck RJ, Bailey GL, Daroca PJ Jr et al. Pentazocine abuse: report of a case with pulmonary arterial cellulose granulomas and pulmonary hypertension. Chest . 1980; 77:227-9. [PubMed 7353425]

242. Tomashefski JF Jr, Hirsch CS, Jolly PN. Microcrystalline cellulose pulmonary embolism and granulomatosis: a complication of illicit intravenous injections of pentazocine tablets. Arch Pathol Lab Med . 1981; 105:89-93. [PubMed 6893924]

243. Farber HW, Mathers JAL Jr, Glauser FL. Gallium scans and serum angiotensin converting enzyme levels in talc granulomatosis and lymphocytic interstitial pneumonitis. South Med J . 1980; 73:1663-7. [PubMed 6255609]

244. Farber HW, Falls R, Glauser FL. Transient pulmonary hypertension from the intravenous injection of crushed, suspended pentazocine tablets. Chest . 1981; 80:178-82. [PubMed 7249763]

245. Farber HW, Fairman RP, Glauser FL. Talc granulomatosis: laboratory findings similar to sarcoidosis. Am Rev Respir Dis . 1982; 125:258-61. [PubMed 6278999]

246. Farber H, Glauser FL. The effect of oral hydralazine on the pulmonary hemodynamics of patients with pulmonary foreign body granulomatosis. Chest . 1982; 82:708-12. [PubMed 7140398]

247. Meador KH, Sharon Z, Lewis EJ. Renal amyloidosis and subcutaneous drug abuse. Ann Intern Med . 1979; 91:565-7. [PubMed 484955]

248. Mizutani T, Lewis RA, Gonatas NK. Medial medullary syndrome in a drug abuser. Arch Neurol . 1980; 37:425-8. [PubMed 7387487]

249. AtLee WE Jr. Talc and corn starch emboli in eyes of drug abusers. JAMA . 1972; 219:49-51. [PubMed 5066587]

250. Kresca LJ, Goldberg MF, Jampol LM. Talc emboli and retinal neovascularization in a drug abuser. Am J Ophthalmol . 1979; 87:334-9. [PubMed 434093]

251. Friberg TR, Gragoudas ES, Regan CDJ. Talc emboli and macular ischemia in intravenous drug abuse. Arch Ophthalmol . 1979; 97:1089-91. [PubMed 444139]

252. Schatz H, Drake M. Self-injected retinal emboli. Ophthalmology . 1979; 86:468-83. [PubMed 530595]

253. Shook JE, Kallman MJ, Martin BR et al. Characterization of the interaction of pentazocine and tripelennamine: drug discrimination and mu-receptor binding assay. Pharmacol Biochem Behav . 1984; 21:877-81. [PubMed 6097919]

254. Tagashira E, Kachur JF, Carter WH et al. Potentiation of narcotic-induced antinociception by tripelennamine in morphine-tolerant and drug-naive mice. J Pharmacol Exp Ther . 1984; 229:214-7. [PubMed 6707938]

255. Shannon HE, Su TP. Effects of the combination of tripelennamine and pentazocine at the behavioral and molecular levels. Pharmacol Biochem Behav . 1982; 17:789-95. [PubMed 6294681]

256. Su TP. Possible explanations of “T's and blues” interaction: tripelennamine and pentazocine are potent ligands for psychotomimetic sigma-opioid receptor. Fed Proc . 1983; 42:1017.

257. Tagashira E, Kachur JF, Carter WH Jr et al. Pentazocine-tripelennamine (“T's and Blues”) substitution studies in morphine-dependent rodents. J Pharmacol Exp Ther . 1984; 231:97-101. [PubMed 6541694]

258. Bhargava HN. Mechanism of toxicity and rationale for use of the combination of pentazocine and pyribenzamine in morphine-dependent subjects. Clin Toxicol . 1981; 18:175-88. [PubMed 7194759]

259. Waller DP, Katz NL, Morris RW. Potentiation of lethality in mice by combinations of pentazocine and tripelennamine. Clin Toxicol . 1980; 16:17-23. [PubMed 7389279]

260. Carlson C. Talwin 50 reformulated to avert “T's and blues” abuse. JAMA . 1983; 249:1689. [PubMed 6827745]

261. Talwin® Nx prescribing information. In: Huff BB, ed. Physicians' desk reference. 39th ed. Oradell, NJ: Medical Economics Company Inc; 1985:2230-2.

262. Wyeth Laboratories. Phenergan® tablets and suppositories prescribing information. Philadelphia; 1984 Oct 1.

263. Aselton P, Hershel J, Milunsky A et al. First-trimester drug use and congenital disorders. Obstet Gynecol . 1985; 65:451-5. [PubMed 3982720]

264. Mortimer EA Jr. Drug toxicity from breast milk. Pediatrics . 1977; 60:780-2. [PubMed 917668]

265. Lin CC, Kim HK, Lim J et al. Steady-state bioavailability of dexbrompheniramine and pseudoephedrine from a repeat-action combination tablet. J Pharm Sci . 1985; 74:25-8. [PubMed 3981411]

266. Friedman H, Greenblatt DJ. The pharmacokinetics of doxylamine: use of automated gas chromatography with nitrogen-phosphorus detection. J Clin Pharmacol . 1985; 25:448-51. [PubMed 4056080]

267. Kohlhof KJ, Stump D, Zizzamia JA. Analysis of doxylamine in plasma by high-performance liquid chromatography. J Pharm Sci . 1983; 72:961-2. [PubMed 6620159]

268. Zierler S, Rothman KJ. Congenital heart disease in relation to maternal use of Bendectin and other drugs in early pregnancy. N Engl J Med . 1985; 313:347-52. [PubMed 4010751]

269. Anon. Indications for Bendectin narrowed. FDA Drug Bull . 1981; 11:1-3. [PubMed 7215728]

270. Anon. Bendectin and pyloric stenosis. FDA Drug Bull . 1983; 13:14-5.

271. Cordero JF, Oakley GP, Greenberg F et al. Is Bendectin a teratogen? JAMA . 1981; 245:2307-10.

272. Unisom®product information. In: Huff BB, ed. Physicians' desk reference for nonprescription drugs. 6th ed. Oradell, NJ: Medical Economics Company Inc; 1985:568.

273. Bendectin® prescribing information. In: Huff BB, ed. Physicians' desk reference. 37th ed. Oradell, NJ: Medical Economics Company Inc; 1983:1345-6.

274. Orme ML. The Debendox saga. BMJ . 1985; 291:918-9. [PubMedCentral][PubMed 3929963]

275. Holmes LB. Teratogen update: Bendectin. Teratology . 1983; 27:277-81. [PubMed 6346560]

276. Kolata G. FDA to reexamine Bendectin data. Science . 1982; 217:335. [PubMed 7046049]

277. More on Bendectin. JAMA . 1981; 246:371-2. Editorial.

278. Smith RJ. Studies support Bendectin safety claim. Science . 1981; 212:1485. [PubMed 7015515]

279. Kolata GB. How safe is Bendectin? Science . 1980; 210:518-9.

280. Check WA. CDC study: no evidence for teratogenicity of Bendectin. JAMA . 1979; 242:2518. [PubMed 490865]

281. Smithells RW, Sheppard S. Teratogenicity testing in humans: a method demonstrating safety of Bendectin. Teratology . 1978; 17:31-6. [PubMed 625707]

282. Morelock S, Hingson R, Kayne H et al. Bendectin and fetal development. Am J Obstet Gynecol . 1982; 142:209-13. [PubMed 7055187]

283. Morelock S, Hingson R, Kayne H et al. Bendectin and fetal development. Am J Obstet Gynecol . 1982; 143:237. [PubMed 6123260]

284. Shapiro S, Heinonen OP, Siskind V et al. Antenatal exposure to doxylamine succinate and dicyclomine hydrochloride (Bendectin) in relation to congenital malformations, perinatal mortality rate, birth weight, and intelligence quotient score. Am J Obstet Gynecol . 1977; 128:480-5. [PubMed 879205]

285. Harron DWG, Griffiths K, Shanks RG. Debendox and congenital malformations in Northern Ireland. Br Med J . 1980; 281:1379-81. [PubMedCentral][PubMed 7437804]

286. Barlow SM, Sullivan FM. Debendox and congenital malformations in Northern Ireland. BMJ . 1981; 282:148-9. [PubMedCentral]

287. Shanks RG, Griffiths K, Harron DWG. Debendox and congenital malformations in Northern Ireland. BMJ . 1981; 282:1972-3. [PubMed 6786693]

288. Fleming DM, Knox JDE, Crombie DL. Debendox in early pregnancy and fetal malformation. BMJ . 1981; 283:99-101. [PubMedCentral][PubMed 6789952]

289. Rothman KJ, Fyler DC, Goldblatt A et al. Exogenous hormones and other drug exposures of children with congenital heart disease. Am J Epidemiol . 1979; 109:433-9. [PubMed 443241]

290. Mitchell AA, Rosenberg L, Shapiro S et al. Birth defects related to Bendectin use in pregnancy: oral clefts and cardiac defects. JAMA . 1981; 245:2311-4. [PubMed 7230459]

291. Jick H, Holmes LB, Hunter JR et al. First-trimester drug use and congenital disorders. JAMA . 1981; 246:343-6. [PubMed 7241780]

292. Gibson GT, Colley DP, McMichael AJ et al. Congenital anomalies in relation to the use of doxylamine/dicyclomine and other antenatal factors: an ongoing prospective study. Med J Aust . 1981; 1:410-4. [PubMed 7254087]

293. Kalter H, Warkany J. Congenital malformations. N Engl J Med . 1983; 309:312. [PubMed 6866057]

294. Nestor JO. Congenital malformations. N Engl J Med . 1983; 309:312. [PubMed 6866057]

295. Eskenazi B, Bracken MB. Bendectin (Debendox) as a risk factor for pyloric stenosis. Am J Obstet Gynecol . 1982; 144:919-24. [PubMed 7148924]

296. Mitchell AA, Schwingl PJ, Rosenberg L et al. Birth defects in relation to Bendectin use in pregnancy: II. Pyloric stenosis. Am J Obstet Gynecol . 1983; 147:737-42. [PubMed 6650593]

297. Golding J, Vivian S, Baldwin JA. Maternal anti-nauseants and clefts of lip and palate. Hum Toxicol . 1983; 2:63-73. [PubMed 6840794]

298. Aselton PJ, Jick H. Additional follow-up of congenital limb disorders in relation to Bendectin use. JAMA . 1983; 250:33-4. [PubMed 6682906]

299. Kalter H, Warkany J. Congenital malformations (second of two parts). N Engl J Med . 1983; 308:491-7. [PubMed 6337336]

300. Grodofsky MP, Wilmott RW. Possible association of use of Bendectin during early pregnancy and congenital lung hypoplasia. N Engl J Med . 1984; 304:732.

301. Hughes DT, Cavanagh N. Chromosomal studies on children with phocomelia, exposed to Debendox during early pregnancy. Lancet . 1983; 2:399. [PubMed 6135891]

302. Smithells RW, Sheppard S. Teratogenicity of Debendox and pyrimethamine. Lancet . 1983; 2:623-4. [PubMed 6136770]

303. Clarke M, Clayton DG. Safety of Debendox. Lancet . 1981; 1:659-60. [PubMed 6110878]

304. Bracken MB, Berg A. Bendectin (Debendox) and congenital diaphragmatic hernia. Lancet . 1983; 1:586. [PubMed 6131274]

305. Mitchell AA, Shapiro S. Bendectin (Debendox) and congenital diaphragmatic hernia. Lancet . 1983; 1:930. [PubMed 6132245]

306. Merrell National laboratories. Decapryn® prescribing information. Cincinnati, OH; 1975 Oct.

307. Gosselin RE, Smith RP, Hodge HC. Clinical toxicology of commercial products. 5th ed. Baltimore: Williams & Wilkins; 1984;III-36-40.

308. Lee CC. Comparative pharmacologic responses to antihistamines in newborn and young rats. Toxicol Appl Pharmacol . 1966; 8:210-7. [PubMed 5956873]

309. Cook TJ, MacQueen DM, Wittig HJ et al. Degree and duration of skin test suppression and side effects with antihistamines: a double blind controlled study with five antihistamines. J Allergy Clin Immunol . 1973; 51:71-7. [PubMed 4405284]

310. Galant SP, Bullock J, Wong D et al. The inhibitory effect of antiallergy drugs on allergen and histamine induced wheal and flare response. J Allergy Clin Immunol . 1973; 51:11-21. [PubMed 4118408]

311. Chipps BE, Talamo RC, Mellits ED et al. Immediate (IgE-mediated) skin testing in the diagnosis of allergic disease. Ann Allergy . 1978; 41:211-5. [PubMed 81630]

312. Galant SP, Zippin C, Bullock J et al. Allergy skin test: I. Antihistamine inhibition. Ann Allergy . 1972; 30:53-63. [PubMed 4400814]

313. Diamond GA, Dilibero RJ. Pharmacologic modification of the immediate intradermal skin reaction. Ann Allergy . 1966; 24:288-90. [PubMed 5328526]

314. Kern GW IV. Letter to the editors. Clin Allergy . 1982; 12:321. [PubMed 6125277]

315. Arnaud A, Vervloet D, Ostorero M et al. Effets des anti-histaminiques (H1 et H2) sur différents types de tests cutanés explorant l'allergie a médiation humorale ou cellulaire. (French; with English abstract.) Nouv Presse Med . 1980; 9:2849. Letter.

316. Johnson CE, Weiner JS, Wagner DS et al. Effect of H1- and H2-receptor blockade on the inhibition of immediate cutaneous reactions. Clin Pharm . 1984; 3:60-4. [PubMed 6141860]

317. Smith JA, Mansfield LE, de Shazo RD. An evaluation of the pharmacologic inhibition of the immediate and late cutaneous reaction to allergen. J Allergy Clin Immunol . 1980; 65:118-21.

318. Gibbs CJ, Coutts II, Jackson SM et al. Skin test wheal size and erythema not reduced by topical antihistamine. BMJ . 1983; 287:1427-8. [PubMedCentral][PubMed 6139139]

319. Filloux F. Toxic encephalopathy caused by topically applied diphenhydramine. J Pediatr . 1986; 108:1018-20. [PubMed 3712143]

320. Schering Corporation. Chlor-Trimeton® Injection prescribing information. Kenilworth, NJ; 1985 Jun.

321. Mansfield LE, Smith JA, Nelson HS. Greater inhibition of dermographia with a combination of H1 and H2 antagonists. Ann Allergy . 1983; 50:264-5. [PubMed 6132569]

322. The United States pharmacopeia, 21st rev, and The national formulary, 16th ed. Rockville, MD: The United States Pharmacopeial Convention, Inc; 1987(Suppl 5):2485.

323. Department of Health and Human Services National Toxicology Program. Toxicology and carcinogenesis studies of chlorpheniramine maleate (CAS No. 113-92-8) in F344/N rats and B6C3F1 mice (gavage studies). Research Triangle Park, NC: National Toxicology Program; 1986 Sept. (NIH publication No. 86-2573; NTP TR No. 317).

324. Kok THHG, Taitz LS, Bennett MJ et al. Drowsiness due to clemastine transmitted in breast milk. Lancet . 1982; 1:914-5. [PubMed 6122135]

325. Sandoz Pharmaceuticals Corporation. Tavist® (clemastine fumarate) Syrup prescribing information. In: Huff BB, ed. Physicians' desk reference. 41st ed. Oradell, NJ: Medical Economics Company Inc; 1987:1792-3.

326. Tham R, Norlander B, Hagermark O et al. Gaschromatography of clemastine (a study of plasma kinetics and biological effect). Arzneimittelforschung . 1978; 28:1017-20. [PubMed 35180]

327. Paton DM, Webster DR. Clinical pharmacokinetics of H1-receptor antagonists (the antihistamines). Clin Pharmacokinet . 1985; 10:477-97. [PubMed 2866055]

328. Food and Drug Administration. Antiemetic drug products for over-the-counter human use; final monograph [21 CFR Parts 310, 366, 369; Docket No. 78N-036A]. Fed Regist . 1987; 52:15866-93.

329. Smith Kline & French Laboratories. Hispril® (diphenylpyraline hydrochloride) Spansule® capsules prescribing information. In: Huff BB, ed. Physician's desk reference. 41st ed. Oradell, NJ: Medical Economics Company Inc; 1987:1918.

330. Westwood Pharmaceuticals Inc. Tacaryl® (methdilazine) Chewable Tablets and Tacaryl® (methdilazine hydrochloride) Tablets/Syrup prescribing information. In: Huff BB, ed. Physician's desk reference. 41st ed. Oradell, NJ: Medical Economics Company Inc.; 1987:2101-2.

331. Food and Drug Administration. Sulfiting agents; labeling in drugs for human use; warning statement. [21 CFR Part 201] Fed Regist . 1986; 51:43900-4.

332. American Medical Association Council on Scientific Affairs. Aspartame: review of safety issues. JAMA . 1985; 254:400-2. [PubMed 2861297]

333. Gossel TA. A review of aspartame: characteristics, safety and uses. US Pharm . 1984; 9:26,28-30.

334. Food and Drug Administration. Aspartame as an inactive ingredient in human drug products; labeling requirements. [21 CFR Part 201] Fed Regist . 1983; 48:54993-5. (IDIS 178728)

335. Food and Drug Administration. Food additives permitted for direct addition to food for human consumption; aspartame. [21 CFR Part 172] Fed Regist . 1983; 48:31376-82. (IDIS 172957)

336. Anon. Aspartame and other sweeteners. Med Lett Drugs Ther . 1982; 24:1-2. [PubMed 7054648]

337. Loan WB, Cuthbert D. Adverse cardiovascular response to oral trimeprazine in children. BMJ . 1985; 290:1548-9. [PubMedCentral][PubMed 3924159]

338. Thomas DL, Vaughan RS, Vickers MD et al. Comparison of temazepam elixir and trimeprazine syrup as oral premedication in children undergoing tonsillectomy and associated procedures. Br J Anaesth . 1987; 59:424-30. [PubMed 2882766]

339. Padfield NL, Twohig MM, Fraser ACL. Temazepam and trimeprazine compared with placebo as premedication in children. Br J Anaesth . 1986; 58:487-93. [PubMed 2870728]

340. Yeh SY, Todd GD, Johnson RE et al. The pharmacokinetics of pentazocine and tripelennamine. Clin Pharmacol Ther . 1986; 39:669-76. [PubMed 3709032]

341. Brand JJ, Perry WLM. Drugs used in motion sickness: a critical review of the methods available for the study of drugs of potential value in its treatment and of the information which has been derived by these methods. Pharmacol Rev . 1966; 18(1 Part II):895-924. [PubMed 5325212]

342. Wood CD, Kennedy RS, Graybiel A. Review of antimotion sickness drugs from 1954-1964. Aerospace Med . 1965; 36:1-4. [PubMed 14243672]

343. Chinn HI, Smith PK. Motion sickness. Pharmacol Rev . 1955; 7:33-82. [PubMed 14370919]

344. Money KE. Motion sickness. Physiol Rev . 1970; 50:1-39. [PubMed 4904269]

345. Cirillo VJ, Tempero KF. Pharmacology and therapeutic use of antihistamines. Am J Hosp Pharm . 1976; 33:1200-7. [PubMed 11685]

346. Douglas WW. Histamine and 5-hydroxytryptamine (serotonin) and their antagonists. In: Gilman AG, Goodman LS, Rall TW et al, eds. Goodman and Gilman's the pharmacological basis of therapeutics. 7th ed. New York: The Macmillan Company; 1985:605-38.

347. Anon. Drugs for relief of nausea and vomiting. Med Lett Drugs Ther . 1974; 16:46-8.

348. Army, Navy, Air Force Motion Sickness Team. Evaluation of drugs for protection against motion sickness aboard transport ships. JAMA . 1956; 160:755-60.

349. Food and Drug Administration. External analgesic drug products for over-the-counter human use; establishment of a monograph and notice of proposed rulemaking. [21 CFR Part 348] Fed Regist . 1979; 44:69768-866.

350. Food and Drug Administration. Cold, cough, allergy, bronchodilator, and antiasthmatic drug products for over-the-counter human use; tentative final monograph for OTC antihistamine drug products. [21 CFR Parts 201, 310, 341, 369] Fed Regist . 1987; 52:31892-914.

351. Spector R, Choudhury AK, Chiang CK et al. Diphenhydramine in Orientals and Caucasians. Clin Pharmacol Ther . 1980; 28:229-34. [PubMed 7398190]

352. Meredith CG, Christian CD, Johnson RF et al. Diphenhydramine disposition in chronic liver disease. Clin Pharmacol Ther . 1984; 35:474-9. [PubMed 6705445]

353. Berlinger WG, Goldberg MJ, Spector R et al. Diphenhydramine: kinetics and psychomotor effects in elderly women. Clin Pharmacol Ther . 1982; 32:387-91. [PubMed 7049503]

354. Graham G, Bolt AG. Half-life of diphenylpyraline in man. J Pharmacokinet Biopharm . 1974; 2:191-5. [PubMed 4156058]

355. American Academy of Pediatrics Committee on Drugs. Antihistamines in topical preparations. Pediatrics . 1973; 51:299-301. [PubMed 4144454]

356. Fastner Z. Antihistamines (H1-receptor antagonists). In: Dukes MNG, ed. Meyler's side effects of drugs. 10th ed. New York: Elsevier Science Publishers BV; 1984:284-9.

357. AMA Department of Drugs. Drug Evaluations. 6th ed. Chicago: American Medical Association; 1986; 1019-20.

358. Arndt KA. Manual of dermatologic therapeutics. 2nd ed. Boston: Little, Brown and Company; 1978:266-72.

359. Calnan CD. Contact dermatitis from drugs. Proc R Soc Med . 1962; 44:39-42.

360. Coskey RJ. Contact dermatitis caused by diphenhydramine hydrochloride. J Am Acad Dermatol . 1983; 8:204-6. [PubMed 6219138]

361. Fisher AA. Systemic eczematous “contact-type” dermatitis medicamentosa. Ann Allergy . 1966; 24:406-20. [PubMed 4223211]

362. Fisher AA. Ethylenediamine dermatitis. Arch Dermatol . 1969; 100:519-20. [PubMed 4243136]

363. Vickers CFH. Dermatitis medicamentosa. Br Med J . 1961; 1:1366-7. [PubMedCentral][PubMed 13781158]

364. Shelley WB, Bennett RG. Primary contact sensitization site: a determinant for the localization of a diphenhydramine eruption. Acta Derm Venereol . 1972; 52:376-8. [PubMed 4117085]

365. Horio T. Allergic and photoallergic dermatitis from diphenhydramine. Arch Dermatol . 1976; 112:1124-6. [PubMed 952531]

366. Emmett EA. Diphenhydramine photoallergy. Arch Dermatol . 1974; 10:249-52.

367. Schreiber MM, Naylor LZ. Antihistamine photosensitivity. Arch Dermatol . 1962; 86:58-62. [PubMed 13909261]

368. Epstein E. Allergy to dermatologic agents. JAMA . 1966; 198:517-20. [PubMed 4380680]

369. Davenport PM, Wilhelm RE. An unusual vasculitis due to diphenhydramine: cutaneous and central nervous system involvement. Arch Dermatol . 1965; 92:577-80. [PubMed 4221165]

370. Lawrence CM, Byrne JPH. Eczematous eruption from oral diphenhydramine. Contact Dermatitis . 1981; 7:276-7. [PubMed 7307489]

371. Serafin WE, Austen KF. Mediators of immediate hypersensitivity reactions. N Engl J Med . 1987; 317:30-4. [PubMed 2438554]

372. Ishikawa S, Sperelakis N. A novel class (H3) of histamine receptors on perivascular nerve terminals. Nature . 1987; 327:158-60. [PubMed 3033517]

373. Arrang JM, Garbarg M, Lancelot JC et al. Highly potent and selective ligands for histamine H3-receptors. Nature . 1987; 327:117-23. [PubMed 3033516]

374. Hill SJ. Histamine receptors branch out. Nature . 1987; 327:104-5. [PubMed 3033514]

375. Arrang JM, Garbarg M, Schwartz JC. Stimulation sélective des aurorécepteurs H3 de l'histamine. (French; with English abstract.) C R Acad Sc Paris . 1987; 304:11-4.

376. Antohe F, Heltianu C, Simionescu N. Further evidence for the distribution and nature of histamine receptors on microvascular endothelium. Microcirc Endothelium Lymphatics . 1986; 3:163-85. [PubMed 2438546]

377. Ehrenpreis S, Kimura I, Kobayashi T et al. Histamine release as the basis for morphine action on bile duct and sphincter of Oddi. Life Sci . 1987; 40:1695-8. [PubMed 2436022]

378. Movat HZ. The role of histamine and other mediators in microvascular changes in acute inflammation. Can J Physiol Pharmacol . 1987; 65:451-7. [PubMed 3555750]

379. Fisher AA. Topical medicaments which are common sensitizers. Ann Allergy . 1982; 49:96-100.

380. Ellis FA, Bundick WR. Appraisal of topical use of antihistamines. JAMA . 1952; 150:773-6.

381. Lauderdale WH, Fred HL, Graver CD. Anaphylactoid reaction to diphenhydramine hydrochloride. Arch Intern Med . 1964; 114:693-5. [PubMed 14216000]

382. Schuller DE. Adverse effects of brompheniramine on pulmonary function in a subset of asthmatic children. J Allergy Clin Immunol . 1983; 72:175-9. [PubMed 6886255]

383. Adverse Drug Reactions Advisory Committee. Antihistamines. Med J Aust . 1982; 1:522.

384. Newill RGD. Photosensitivity caused by promethazine. Br Med J . 1960; 2:359-60. [PubMedCentral][PubMed 14426802]

385. Epstein S, Rowe RJ. Photoallergy and photocross-sensitivity to Pheneugan. J Invest Dermatol . 1957; 28:319-26.

386. Adverse Drug Reactions Advisory Committee. Antihistamine sensitivity. Aust Prescr . 1979; 3:9.

387. Adverse Drug Reactions Advisory Committee. Treatment worse than disease? Aust Prescr . 1980; 4:44.

388. Lauderdale WH, Fred HL, Graver CD. Anaphylactoid reaction to diphenhydramine hydrochloride. Arch Intern Med . 1964; 114:693-5. [PubMed 14216000]

389. Soter NA, Austen KF. The diversity of mast cell-derived mediators: implications for acute, subacute, and chronic cutaneous inflammatory disorders. J Invest Dermatol . 1976; 67:313-9. [PubMed 61246]

390. Food and Drug Administration. Cold, cough, allergy, bronchodilator, and antiasthmatic drug products for over-the-counter human use; tentative final monograph for combination drug products. [21 CFR Part 341] Fed Regist . 1988; 53:30522-64.

391. Merck & Co. Periactin® (cyproheptadine) tablets and syrup prescribing information. West Point, PA; 1999 Sept.

392. Larrey D, Geneve J, Pessayre D et al. Prolonged cholestasis after cyproheptadine-induced acute hepatitis. J Clin Gastroenterol . 1987; 9:102-4. [PubMed 3559100]

393. Merrell Dow Pharmaceuticals Inc. Seldane® (terfenadine) prescribing information. Cincinnati, OH; 1987 Jan.

394. Larrey D, Palazzo L, Benhamou JP. Terfenadine and hepatitis. Ann Intern Med . 1985; 103:634. [PubMed 2864011]

395. Henry DA, Lowe JM, Donnelly T. Jaundice during cyproheptadine treatment. Br Med J . 1978; 1:753. [PubMedCentral][PubMed 630329]

396. Karkalas Y, Lal H. Jaundice following therapy with imipramine and cyproheptadine. Clin Toxicol . 1971; 4:47-53. [PubMed 5097484]

397. Hendeles L, Weinberger M, Wong L. Medical management of noninfectious rhinitis. Am J Hosp Pharm . 1980; 37:496-504. [PubMed 7377212]

398. Bryant BG, Cormier JF. Cold and allergy products. In: American Pharmaceutical Association. Handbook of nonprescription drugs. 8th ed. Washington, DC: American Pharmaceutical Association; 1986:127-74.

399. Food and Drug Administration. General guidelines for OTC drug combination products. [Docket No. 78D-0322, Dockets Management Branch.] 1978 Sep. (Notice of availability published in Fed Regist . 1978; 43:55466.)

400. Doyle WJ, McBride TP, Skoner DP et al. A double-blind, placebo-controlled clinical trial of the effect of chlorpheniramine on the response of the nasal airway, middle ear and eustachian tube to provocative rhinovirus challenge. Pediatr Infect Dis J . 1988; 7:229-38. [PubMed 3282216]

401. Crutcher JE, Kantner TR. The effectiveness of antihistamines in the common cold. J Clin Pharmacol . 1981; 21:9-15. [PubMed 7012191]

402. Gaffey MJ, Gwaltney JM Jr, Sastre A et al. Intranasally and orally administered antihistamine treatment of experimental rhinovirus colds. Am Rev Respir Dis . 1987; 136:556-60. [PubMed 3307567]

403. American Academy of Pediatrics Committee on Drugs. Ethanol in liquid preparations intended for children. Pediatrics . 1984; 73:405-7. [PubMed 6701068]

404. Janssen Pharmaceutical. Hismanal®(astemizole) tablets prescribing information. Piscataway, NJ; 1988 Dec.

405. Richards DM, Brogden RN, Heel RC et al. Astemizole: a review of its pharmacodynamic properties and therapeutic efficacy. Drugs . 1984; 28:38-61. [PubMed 6204835]

406. Mann KV, Crowe JP, Tietze KJ. Nonsedating histamine H1-receptor antagonists. Clin Pharm . 1989; 8:331-44. [PubMed 2568212]

407. Food and Drug Administration. Nighttime sleep-aid products for over-the-counter human use; final monograph. [21 CFR Part 338] Fed Regist . 1989; 54:6814-27. (IDIS 250549)

408. Harvey SC. Hypnotics and sedatives. In: Gilman AG, Goodman L, Rall TW et al, eds. Goodman and Gilman's the pharmacological basis of therapeutics. 7th ed. New York: The Macmillan Company; 1985:339-71.

409. Roila F, Donati D, Basurto C et al. Diphenhydramine and acute dystonia. Ann Intern Med . 1989; 111:92-3. [PubMed 2735633]

410. Mendoza FS, Atiba JO, Krensky AM et al. Rhabdomyolysis complicating doxylamine overdose. Clin Pediatr . 1987; 26:595-7.

411. Parke-Davis. Benadryl® (diphenhydramine hydrochloride injection) prescribing information. In: Physicians' desk reference. 54th ed. Montvale, NJ: Medical Economics Company Inc; 2000:2234.

412. Clark RF, Vance MV. Massive diphenhydramine poisoning resulting in wide-complex tachycardia: successful treatment with sodium bicarbonate. Ann Emerg Med . 1992; 21:318-21. [PubMed 1311158]

413. Hoechst Marion Roussel. Seldane® (terfenadine) tablets prescribing information. Kansas City, MO: 1997 Sep.

414. Davies AJ, Harindra V, McEwan A et al. Cardiotoxic effect with convulsions in terfenadine overdose. BMJ . 1989; 298:325. [PubMedCentral][PubMed 2564285]

415. Dear doctor letter regarding important drug warning of Seldane®. Cincinnati, OH: Marion Merrell Dow; 1990 Aug 6.

416. Monahan BP, Ferguson CL, Killeary ES et al. Torsades de pointes occurring in association with terfenadine use. JAMA . 1990; 264:2788-90. [PubMed 1977935]

417. Marion Merrell Dow, Kansas City, MO: Personal communication.

418. Cruzan S (US Food and Drug Administration). HHS News. Press release No. P92-22. 1992 Jul 7.

419. Marion Merrell Dow. Dear health care professional letter regarding appropriate use of Seldane®. Kansas City, MO: July 7, 1992.

420. Zimmerman M, Duruz H, Guinand O et al. Torsades de pointes after treatment with terfenadine and ketoconazole. Eur Heart J . 1992; 13:1002-3. [PubMed 1644069]

421. Bastecky J, Kvasnicka J, Vortel J et al. [Severe antihistamine poisoning complicated by ventricular tachycardia.] Vnitr Lek . 1990; 36:266-9.

422. Venturini E, Borghi E, Maurini V et al. [Prolongation of the Q-T interval and hyperkinetic ventricular arrhythmias probably induced by terfenadine use in liver cirrhosis patients]. Recenti Prog Med . 1992; 83:21-2. [PubMed 1561478]

423. MacConnell TJ, Stanners AJ. Torsades de pointes complicating treatment with terfenadine. BMJ . 1991; 302:1469. [PubMedCentral][PubMed 1676921]

424. Revelle M (US Food and Drug Administration). HHS News. Press release No. P92-25. 1992 Jul 20.

425. Simons FER, Kesselman MS, Giddins NG et al. Astemizole-induced torsade de pointes. Lancet . 1988; 2:624. [PubMed 2900995]

426. Tobin JR, Doyle TP, Ackerman AD et al. Astemizole-induced cardiac conduction disturbances in a child. JAMA . 1991; 266:2737-40. [PubMed 1942426]

427. Snook J, Boothman-Burrell D, Watkins J et al. Torsades de pointes ventricular tachycardia associated with astemizole overdose. Br J Clin Pract . 1988; 42:257-9. [PubMed 2905156]

428. Kingswood JC, Routledge PA, Lazarus JH. A report of overdose with astemizole. Hum Toxicol . 1986; 5:43-4. [PubMed 3081429]

429. Clark A, Love H. Astemizole-induced ventricular arrhythmias: an unexpected cause of convulsions. Int J Cardiol . 1991; 33:165-7. [PubMed 1937973]

430. Anon. Canada moving Seldane and Hismanal behind the counter. FDC Rep. July 20, 1992; T&G-14.

431. Bastecky J, Kvasnicka J, Vortel J et al. [Severe antihistamine poisoning complicated by ventricular tachycardia.] Vnitr Lek . 1990; 36:266-9.

432. Bishop RO, Gaudry PL. Prolonged Q-T interval following astemizole overdose. Arch Emerg Med . 1989; 6:63-5. [PubMedCentral][PubMed 2565725]

433. Klaumer MA. Dear doctor letter regarding the potential for serious cardiovascular effects in patients taking Hismanal® (astemizole). Titusville, NJ: Janssen Pharmaceutica; July 20, 1992.

434. Anon. Safety of terfenadine and astemizole. Med Lett Drugs Ther . 1992; 34:9-10. [PubMed 1732711]

435. Anon. Astemizole another non-sedating antihistamine. Med Lett Drugs Ther . 1989; 31:43-4. [PubMed 2565524]

436. Clause DW, Zach GA. Reaction to diphenhydramine hydrochloride (Benadryl) used as a local anesthetic. Gen Dent . 1989; 37:426-7. [PubMed 2637894]

437. Ramsdell WM. Severe reaction to diphenhydramine. Letter. J Am Acad Dermatol . 1989; 21:1318-20. [PubMed 2584476]

438. Rinder CS, D'Amato SL, Rinder HM et al. Survival of complicated diphenhydramine overdose. Crit Care Med . 1988; 16:1161-2. [PubMed 3168512]

439. Giotti A, Zilletti L. Antiarrhythmic actions of antihistamines. Pharmacol Ther Part B . 1976; 2:863-900.

440. Riccioppo Neto F. Effects of cyproheptadine on electrophysiological properties of isolated cardiac muscle of dogs and rabbits. Br J Pharmacol . 1983; 80:335-41. [PubMedCentral][PubMed 6652381]

441. Dreifus LS, McGarry TF, Watanabe Y et al. Clinical and physiologic effects of antazoline, a new antiarrhythmic agent. Am Heart J . 1963; 65:607-14.

442. Freedberg RS, Friedman GR, Palu RN et al. Cardiogenic shock due to antihistamine overdose: reversal with intra-aortic balloon counterpulsation. JAMA . 1987; 257:660-1. [PubMed 3098994]

443. Mathews DR, McNutt B, Okerholm R et al. Torsades de pointes occurring in association with terfenadine use. JAMA . 1991; 266:2375-6. [PubMed 1920744]

444. Cortese L, Bjornson DC. Potential interaction between terfenadine and macrolide antibiotics. Clin Pharm . 1992; 11:675. [PubMed 1511540]

445. Honig PK, Zamani K, Woosley RL et al. Erythromycin changes terfenadine pharmacokinetics & electrocardiographic pharmacodynamics. Clin Pharmacol Ther . 1992; 51:156.

446. Cortese LM, Bjornson DC. Comment: the new macrolide antibiotics and terfenadine. Ann Pharmacother . 1992; 26:1019. [PubMed 1504390]

447. Anon. Labeling change to reflect drug interaction between terfenadine and ketoconazole. FDA Med Bull . 1991; 21(Jul):4-5.

448. Nightingale SL. Warnings issued on nonsedating antihistamines terfenadine and astemizole. JAMA . 1992; 268:705. [PubMed 1322467]

449. Anon. New boxed warnings added for Seldane, Hismanal. FDA Med Bull . 1992; 22(Sep):2-3.

450. Hismanal® (astemizole) tablets prescribing information. In: Physicians' desk reference. 46th ed. Montvale, NJ; Medical Economics Company Inc; 1992:1138-9.

451. Filloux F. Toxic encephalopathy caused by topically applied diphenhydramine. J Pediatr . 1976; 108:1018-20.

452. Woodward GA, Baldassano RN. Topical diphenhydramine toxicity in a five year old with varicella. Pediatr Emerg Care . 1988; 4:18-20. [PubMed 3362727]

453. Craft TM. Torsades de pointes after astemizole overdose. BMJ . 1986; 292:660. [PubMedCentral][PubMed 2868774]

454. Reviewers' comments (personal observations).

455. Roche. Posicor® (mibefradil dihydrochloride) tablets prescribing infromation. Nutley, NJ; 1997 Jun.

456. Janssen Pharmaceutica, Titusville, NJ: Personal communication.

457. Janssen Pharmaceutica. Sporanox®(itraconazole) capsules prescribing information. Titusville, NJ; 1992 Oct.

458. Janssen Pharmaceutica. Nizoral® (ketoconazole) tablets prescribing information. Titusville, NJ; 1992 Oct.

459. Janssen Pharmaceutica. Hismanal® (astemizole) tablets prescribing information. Titusville, NJ; 1992 Oct.

460. Klaumer MA. Dear health care professional letter regarding revisions to the Hismanal®(astemizole) package insert concerning cardiac arrhythmias. Titusville, NJ: Janssen Pharmaceutica; July 20, 1992.

461. Wiley JF II, Gleber ML, Henretig FM et al. Cardiotoxic effects of astemizole overdose in children. J Pediatr . 1992; 120:799-802. [PubMed 1578320]

462. Chen Y, Gillis RA, Woosley RL. Block of delayed rectifier potassium current, IK, by terfenadine in cat ventricular myocytes. J Am Coll Cardiol . 1991; 17(Suppl A):140A.

463. Levi R, Chenouda AA, Trzeciakowski JP et al. Dysrhythmias caused by histamine release in guinea pig and human hearts. Klin Wochenschr . 1982; 60:965-71. [PubMed 6182358]

464. Levi R, Allan G, Zavecz JH. Cardiac histamine receptors. Fed Proc . 1976; 35:1942-7. [PubMed 5315]

465. Levi R, Capurro N, Lee CH. Pharmacological characterization of cardiac histamine receptors: sensitivity to H1- and H2-receptor agonists and antagonists. Eur J Pharmacol . 1975; 30:328-35. [PubMed 236192]

466. Honig PK, Woosley RL, Zamani K et al. Changes in the pharmacokinetics and electrocardiographic pharmacodynamics of terfenadine with concomitant administration of erythromycin. Clin Pharmacol Ther . 1992; 52:231-8. [PubMed 1526078]

467. Food and Drug Administration. Cold, cough, allergy, bronchodilator, and antiasthmatic drug products for over-the-counter human use; final monograph for OTC antihistamine drug products. 21 CFR Parts 201, 310, 341, and 369. Final rule. [Docket No. 76N-052H] Fed Regist . 1992; 57:58356-76.

468. Schering-Plough. Disophrol® Chronotabs® patient information. Kenilworth, NJ. Undated.

469. Wallace. Rynatuss® tablets and pediatric suspension prescribing information. In: Physicians' desk reference. 47th ed. Montvale, NJ: Medical Economics Company Inc; 1993:2503.

470. Schering Corp. Claritin® product information. Kenilworth, NJ; 1995 Sep.

471. Quercia RA, Broisman L. Focus on loratadine: a new second-generation nonsedating H1-receptor antagonist. Hosp Formul . 1993; 28:137-53.

472. Barenholtz AH, McLeod DC. Loratadine: a nonsedating antihistamine with once-daily dosing. DICP . 1989; 23:445-50. [PubMed 2525847]

473. Simons FE. Loratadine, a non-sedating H1-receptor antagonist (antihistamine). Ann Allergy . 1989; 63:266-8. [PubMed 2572187]

474. Clissold SP, Sorkin EM, Goa KL. Loratadine: a preliminary review of its pharmacodynamic properties and therapeutic efficacy. Drugs . 1989; 37:42-57. [PubMed 2523301]

475. Honig PK, Wortham DC, Zamani K et al. Terfenadine-ketoconazole interaction: pharmacokinetic and electrocardiographic consequences. JAMA . 1993; 269:1513-8. [PubMed 8445813]

476. Woosley RL, Chen Y, Freiman JP et al. Mechanism of the cardiotoxic actions of terfenadine. JAMA . 1993; 269:1532-6. [PubMed 8445816]

477. Peck CC, Temple R, Collins JM. Understanding consequences of concurrent therapies. JAMA . 1993; 269:1550-2. [PubMed 8445821]

478. Pohjola-Sintonen S, Viitasalo M, Toivonen L et al. Torsades de pointes after terfenadine-itraconazole interaction. BMJ . 1993; 306:186.

479. Terfenadine/azole antifungal agents. In: Tatro DS, Olin BR, Hebel SK, eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1993(April):685a.

480. Nonsedating antihistamines/macrolide antibiotics. In: Tatro DS, Olin BR, Hebel SK, eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1995(July):110c.

481. Meltzer EO. To use or not to use antihistamines in patients with asthma. Ann Allergy . 1990; 64(Part II):183-6. [PubMed 1967918]

482. Lantner R, Tobin MC. Pharmacist advice to asthmatics regarding antihistamine use. Ann Allergy . 1991; 66:411-3. [PubMed 2035904]

483. Berlex. Betapace® (sotalol hydrochloride) prescribing information. Wayne, NJ; 1992 Jul.

484. Pierson WE, Virant FS. Antihistamines in asthma. Ann Allergy . 1989; 63(Part II):601-2. [PubMed 2574551]

485. Food and Drug Administration. Antiemetic drug products for over-the-counter human use; proposed amendment to the monograph. 21 CFR Part 336. Notice of proposed rulemaking. [Docket No. 92N-0346] Fed Regist . 1993; 58:45216-7.

486. Food and Drug Administration. Sleep aids and antiemetics. From: FDA Bulletin Board. 1993 Aug 26.

487. Simons FER, Simons KJ. The pharmacology and use of H1-receptor-antagonist drugs. N Engl J Med . 1994; 330:1663-70. [PubMed 7909915]

488. Schering. Claritin® (loratadine) tablets prescribing information. In: Physicians' desk reference. 48th ed. Montvale, NJ: Medical Economics Company Inc; 1994(Suppl A):A122.

489. Erythromycin interactions: loratadine (Claritin). In: Hansten PD, Horn JR. Drug interactions and updates. Vancouver, WA: Applied Therapeutics, Inc; 1994:748-9.

490. Crane JK, Shih HT. Syncope and cardiac arrythmia due to an interaction between itraconazole and terfenadine. Am J Med . 1993; 95:445-6. [PubMed 8213879]

491. Food and Drug Administration. Cold, cough, allergy, bronchodilator, and antiasthmatic drug products for over-the-counter human use; amendment of final monograph for OTC antitussive drug products. 21 CFR Part 341. Final rule. [Docket No. 89P-0040] Fed Regist . 1994; 59:29172-4.

492. Kaplan AP. Anaphylaxis. In: Wyngaarden JB, Smith LH Jr, Bennett JC, eds. Cecil textbook of medicine. 19th ed. Philadelphia: WB Saunders Company; 1992:1462-5.

493. Austen KF. Diseases of immediate type hypersensitivity. In: Isselbacher KJ, Braunwald E, Wilson JD et al, eds. Harrison's principles of internal medicine. 13th ed. New York: McGraw-Hill Company; 1994:1632-4.

494. Burroughs Wellcome Co. Semprex®-D (acrivastine and pseudoephedrine HCl) capsules. Research Triangle Park, NC; 1994 April.

495. Brogden RN, McTavish D. Acrivastine: a review of its pharmacological properties and therapeutic efficacy in allergic rhinitis, urticaria and related disorders. Drugs . 1991; 41:927-40. [PubMed 1715267]

496. Aaronson DW. Comparative efficacy of H1 antihistamines. Ann Allergy . 1991; 67:541-7. [PubMed 1683523]

497. Meltzer EO. Comparative safety of H1 antihistamines. Ann Allergy . 1991; 67:625-33. [PubMed 1684274]

498. Simons FER. H1-receptor antagonists: comparative tolerability and safety. Drug Safety . 1994; 10:350-80. [PubMed 7913608]

499. Cohen AF, Hamilton MJ, Peck AW. The effects of acrivastine (BW825C), diphenhydramine and terfenadine in combination with alcohol on human CNS performance. Eur J Clin Pharmacol . 1987; 32:279-88. [PubMed 2885203]

500. Weintraub M. Histamine H1 antagonists. N Engl J Med . 1994; 331:1019. [PubMed 7916125]

501. Parke-Davis. Benadryl 25 tablets and kapseals (25 mg diphenhydramine HCl) prescribing information. In: Physicians' desk reference. 48th ed. Montvale, NJ: Medical Economics Company Inc; 1994(Suppl A):A36.

502. Schering, Kenilworth, NJ: Personal communication.

503. Brannan MD, Reidenberg P, Radwanski E et al. Loratadine administered concomitantly with erythromycin: pharmacokinetic and electrocardiographic evaluations. Clin Pharmacol Ther . 1995; 58:269-78. [PubMed 7554700]

504. Woosley RL, Chen Y, Freiman JP et al. Mechanism of the cardiotoxic actions of terfenadine. JAMA . 1993; 269:1532-6. [PubMed 8445816]

505. Good AP, Rockwood R, Schad P. Loratadine and ventricular tachycardia. Am J Cardiol . 1994; 74:207. [PubMed 7517624]

506. Woosley R, Darrow WR. Analysis of potential adverse drug reactions—a case of mistaken identity. Am J Cardiol . 1994; 74:208-9. [PubMed 8023797]

507. Biglin KE, Faraon MS, Constance TD et al. Drug-induced torsades de pointes: a possible interaction of terfenadine and erythromycin. Ann Pharmacother . 1994; 28:282. [PubMed 8173153]

508. Ketoconazole (Nizoral) interactions: astemizole (Hismanal). In: Hansten PD, Horn JR. Drug interactions and updates. Vancouver, WA: Applied Therapeutics, Inc; 1994:751.

509. Pfizer Laboratories. Zyrtec® (cetirizine hydrochloride) tablets and syrup prescribing information. New York, NY; 1998 May.

510. Parke Davis. Eryc® (erythromycin delayed-release capsules) prescribing information (dated 1994 June). In Physicians' desk reference. 50th ed. Montvale, NJ: Medical Economics Company Inc; 1996:1915-7.

511. Klausner MA. Dear healthcare provider letter regarding new information concerning drug interaction of astemizole with quinine. Titusville, NJ; 1996 Mar 25.

512. Janssen Pharmaceutica. Hismanal® (astemizole tablets) prescribing information. Titusville, NJ. 1998 Feb.

513. Janssen Pharmaceutica, Titusville, NJ: Personal communication.

514. Hoechst Marion Roussel, Kansas City, MO: Personal communication.

515. Thompson D, Oster G. Use of terfenadine and contraindicated drugs. JAMA . 1996; 275:1339-41. [PubMed 8614120]

516. Hoechst Marion Roussel. Allegra® (fexofenadine hydrochloride) capsules prescribing information. Kansas City, MO; 1996 Jul.

517. Hoechst Marion Roussel, Inc. Product information form for American hospital formulary service: Allegra® (fexofenadine HCl). Kansas City, MO: 1996.

518. Hoechst Marion Roussel. Seldane-D® (terfenadine and pseudoephedrine hydrochloride) extended-release tablets prescribing information. Kansas City, MO; 1997 Sep.

519. Turner RB, Sperber SJ, Sorrentino JV et al. Effectiveness of clemastine fumarate for treatment of rhinorrhea and sneezing associated with the common cold. Clin Infect Dis . 1997; 25:824-30. [PubMed 9356796]

520. Douglass JA, Dhami D, Gurr CE et al. Influence of interleukin-8 challenge in the nasal mucosa in atopic and nonatopic subjects. Am J Respir Crit Care Med . 1994; 150:1108- 13. [PubMed 7921444]

521. Proud D, Naclerio RM, Gwaltney JM et al. Kinins are generated in nasal secretions during natural rhinovirus colds. J Infect Dis . 1990; 161:120-3. [PubMed 2295843]

522. Proud D, Gwaltney JM Jr., Hendley JO et al. Increased levels of interleukin-1 are detected in nasal secretions of volunteers during experimental rhinovirus colds. J Infect Dis . 1994; 169:1007-13. [PubMed 8169385]

523. Turner RB. Elaboration of intereleukin 8 from fibroblast cells and human nasal epithelium in response to rhinovirus challenge. Program and abstracts of the thirty-fourth Interscience Conference on Antimicrobial Agents and Chemotherapy. Orlando, FL: 1994. Abstract No. B43.

524. Berkowitz RB, Tinkelman DG. Evaluation of oral terfenadine for treatment of the common cold. Ann Allergy . 1991; 67:593-7. [PubMed 1750722]

525. Gaffey MJ, Gwaltney JM, Sastre A et al. Intranasally and orally administered antihistamine treatment of experimental rhinovirus colds. Am Rev Respis Dis . 1987; 136:556-560.

526. Wallace Laboratories. Astelin® (azelastine hydrochloride) nasal spray prescribing information. Cranbury, NJ; 1996 Oct.

527. Wallace Laboratories. Astelin® (azelastine hydrochloride) nasal spray product monograph. Cranbury, NJ; 1997 Jan.

528. Wallace Laboratories. Product information form for American hospital formulary service: Astelin® (azelastine hydrochloride) nasal spray. Cranbury, NJ; 1996 Oct 30.

529. Anon. Azelastine spray for allergic rhinitis. Med Lett Drugs Ther . 1997; 39:45-7. [PubMed 9150688]

530. Pelucchi A, Chiapparino A, Mastropasqua B et al. Effect of intranasal azelastine and beclomethasone dipropionate on nasal symptoms, nasal cytology, and bronchial responsiveness to methacholine in allergic rhinitis in response to grass pollens. J Allergy Clin Immunol . 1995; 95:515-23. [PubMed 7852667]

531. Spaeth J, Schultze V, Klimek L et al. Azelastine reduces histamine-induced swelling of nasal mucosa. ORL J Otorhin Relat Spec . 1996; 58:157-63.

532. LaForce C, Dockhorn RJ, Prenner BM et al. Safety and efficacy of azelastine nasal spray (Astelin NS) for seasonal allergic rhinitis: a 4-week comparative multicenter trial. Ann Allergy Asthma Immunol . 1996; 76:181-8. [PubMed 8595539]

533. Gastpar H, Nolte D, Aurich R et al. Comparative efficacy of azelastine nasal spray and terfenadine in seasonal and perennial rhinitis. Allergy . 1994; 49:152-8. [PubMed 7911010]

534. Charpin D, Godard P, Garay RP et al. A multicenter clinical study of the efficacy and tolerability of azelastine nasal spray in the treatment of seasonal allergic rhinitis: a comparison with oral cetirizine. Eur Arch Otorhinolaryngol . 1995; 252:455-8. [PubMed 8719584]

535. Ratner PH, Findlay SR, Hampel F et al. A double-blind, controlled trial to assess the safety and efficacy of azelastine nasal spray in seasonal allergic rhinitis. J Allergy Clin Immunol . 1994; 94:818-25. [PubMed 7963150]

536. Weiler JM, Meltzer EO, Benson PM et al. A dose-ranging study of the efficacy and safety of azelastine nasal spray in the treatment of seasonal allergic rhinitis with an acute model. J Allergy Clin Immunol . 1994; 94:972-80. [PubMed 7798545]

537. Passali D, Piragine F. A comparison of azelastine nasal spray and cetirizine tablets in the treatment of allergic rhinitis. J Int Med Res . 1994; 22:17-23. [PubMed 8187941]

538. Conde Hernández DJ, Palma Aqilar JL, Delgado Romero J. Comparison of azelastine nasal spray and oral ebastine in treating seasonal allergic rhinitis. Curr Res Med Opin . 1995; 13:299-304.

539. Davies RJ, Bagnall AC, McCabe RN et al. Antihistamines: topical vs oral administration. Clin Exp Allergy . 1996; 26(Suppl 3):11-7. [PubMed 8735853]

540. Crutcher JE, Kantner TR. The effectiveness of antihistamines in the common cold. J Clin Pharmacol. 1981; 21:9-15.

541. Benton RE, Honig PK, Zamani K et al. Grapefruit juice alters tefenadine pharmacokinetics, resulting in prolongation of repolarization on the electrocardiogram. Clin Pharmacol Ther . 1996; 59:383-8. [PubMed 8612381]

542. Rau SE, Bend JR, Arnold MO et al. Grapefruit juice-terfenadine single-dose interaction: magnitude, mechanism, and relevance. Clin Pharmacol Ther . 1997; 61:401- 9. [PubMed 9129557]

543. Honig PK, Wortham DC, Lazarev A et al. Grapefruit juice alters the systemic bioavailability and cardiac repolarization of terfenadine in poor metabolizers of terfenadine. J Clin Pharmacol . 1996; 36:345-51. [PubMed 8728348]

544. Ameer B, Weintraub RA. Drug interactions with grapefruit juice. Clin Pharmacokinet . 1997; 33:103-21. [PubMed 9260034]

545. Abbott Laboratories. Norvir® (ritonavir) capsules and oral solution prescribing information. North Chicago, IL; 1996 Nov.

546. Piscitelli SC, Flexner C, Minor JR et al. Drug interactions in patients infected with human immunodeficiency virus. Clin Infect Dis . 1996; 23:685-93. [PubMed 8909827]

547. Merck. Crixivan (indinavir sulfate) capsules prescribing information. In: Physicians' desk reference. 51st ed. Montvale, NJ: Medical Economics Company Inc; 1997:1670-3.

548. Agouron. Viracept® (nelfinavir) tablets and oral powder prescribing information. La Jolla, CA. 1997 Jul.

549. Roche. Invirase® (saquinavir maleate) capsules prescribing information. In: Physicians' desk reference. 51st ed. Montvale, NJ: Medical Economics Company Inc; 1997:2291- 4.

550. Pfizer. Zoloft®(sertraline) tablets prescribing information. New York, NY; 1997 Jul.

551. Solvay. Luvox® (fluvoxamine maleate) tablets prescribing information. In: Physicians' desk reference. 51st ed. Montvale, NJ: Medical Economics Company Inc; 1997:2273- 6.

552. Nonsedating antihistamines/fluvoxamine. In: Tatro DS, Olin BR, Hebel SK eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1997 (Oct):110.

553. Bristol-Myers Squibb. Serzone® (nefazodone hydrochloride) tablets prescribing information. In: Physicians' desk reference. 51st ed. Montvale, NJ: Medical Economics Company Inc; 1997: 776-9.

554. Nonsedating antihistamines/indinavir. In: Tatro DS, Olin BR, Hebel SK eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1997 (Oct):110c.

555. Nonsedating antihistamines/food (grapefruit juice). In: Tatro DS, Olin BR, Hebel SK eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1997 (Oct):110a.

556. Food and Drug Administration. Labeling of diphenhydramine-containing drug products for over-the-counter human use. 21 CFR Parts 336, 338, 341, 348. Proposed rule. [Docket No. 97N-0128] Fed Regist . 1997; 62:45767-74.

557. Chan CYJ, Wallander KA. Diphenhydramine toxicity in three children with varicella- zoster infection. DICP . 1991; 25:130-2. [PubMed 2058184]

558. Warner-Lambert. Benadryl® Itch Relief Stick Extra Strength patient information (undated). In: Physicians' desk reference for nonprescription drugs. 18th ed. Montvale, NJ: Medical Economics Company Inc; 1997:827.

559. Warner-Lambert. Benadryl® Itch Stopping Cream Original Strength and Extra Strength patient information (undated). In: Physicians' desk reference for nonprescription drugs. 18th ed. Montvale, NJ: Medical Economics Company Inc; 1997:827.

560. Warner-Lambert. Benadryl® Itch Stopping Spray Original Strength and Extra Strength patient information (undated). In: Physicians' desk reference for nonprescription drugs. 18th ed. Montvale, NJ: Medical Economics Company Inc; 1997:827-8.

561. Warner-Lambert. Benadryl® Itch Stopping Gel Original Strength and Extra Strength patient information (undated). In: Physicians' desk reference for nonprescription drugs. 18th ed. Montvale, NJ: Medical Economics Company Inc; 1997:827.

562. Food and Drug Administration. Cold, cough, allergy, bronchodilator, and antiasthmatic drug products for over-the-couunter human use; products containing diphenhydramine citrate or diphenhydramine hydrochloride; enforcement policy. 21 CFR Part 341. Final rule. [Docket No. 76N-052G] Fed Regist . 1996; 61:15700-3.

563. Warner-Lambert. Caladryl® lotion, cream for kids, and clear lotion patient information (undated). In: Physicians' desk reference for nonprescription drugs. 18th ed. Montvale, NJ: Medical Economics Company Inc; 1997:830.

564. Smith MBH, Feldman W. Over-the-counter cold medications: a critical review of clinical trials between 1950 and 1991. JAMA . 1993; 269: 2258-63. [PubMed 8097268]

565. D Agostino RB, Weintraub M. Meta-analysis: a method for synthesizing research. Clin Pharmacol Ther . 1995; 58:605-16. [PubMed 8529325]

566. National Asthma Education Program. Expert Panel Report II: guidelines for the diagnosis and management of asthma. 1997 Feb.

567. Reviewers' comments (personal observations) on Fexofenadine (Uses: Other Uses).

568. Cerio R, Lessof MH. Treatment of chronic idiopathic urticaria with terfenadine. Clin Allergy . 1984; 14:139-41. [PubMed 6423314]

569. Fredriksson T, Hersle K, Hjorth N et al. Terfenadine in chronic urticaria: a comparison with clemastine and placebo. Cutis . 1986; 38:128-30. [PubMed 2874958]

570. Ferguson J, MacDonald KJS, Kenicer KJA. Terfenadine and placebo compared in the treatment of chronic idiopathic urticaria: a randomized double-blind study. Br J Clin Pharmacol . 1985; 20:639-41. [PubMedCentral][PubMed 3937549]

571. Paul E, Bodeker RH. Treatment of chronic urticaria with terfenadine and ranitidine: a randomized double-blind study in 45 patients. Eur J Clin Pharmacol . 1986; 31:277-80. [PubMed 2878811]

572. Cainelli T, Seidenari S, Valsecchi R et al. Double-blind comparison of astemizole and terfenadine in the treatment of chronic urticaria. Pharmacotherapeutica . 1986; 4:679-86.

573. Ormerod AD, Baker R, Watt J et al. Terfenadine and brompheniramine maleate in urticaria and dermographism. Dermatologica . 1986; 173:5-8. [PubMed 2875904]

574. Awni WM, Cavanaugh JH, Leese P et al. The pharmacokinetic and pharmacodynamic interaction between zileuton and terfenadine. Eur J Clin Pharmacol . 1997; 52:49-54. [PubMed 9143867]

575. McGann KP, Pribanich S, Graham JA et al. Diphenhydramine toxicity in a child with varicella: a case report. J Fam Pract . 1992; 35:210,213-4. [PubMed 1645115]

576. Woodward GA, Baldassano RN. Topical diphenhydramine toxicity in a five year old with varicella. Pediatr Emerg Care . 1988; 4:18-20. [PubMed 3362727]

577. Sale ME, Barbey JT, Woosley RL et al. The electrocardiographic effects of cetirizine in normal subjects. Clin Pharmacol Ther . 1994; 56:295-301. [PubMed 7924125]

578. Barnes CL, McKenzie CA, Webster KD et al. Cetirizine: a new, nonsedating antihistamine. Ann Pharmacother . 1993; 27:464-70. [PubMed 8477125]

579. Anon. Cetirizine—a new antihistamine. Med Lett Drugs Ther . 1996; 38:21-3. [PubMed 8598822]

580. Simons FER. H1-Receptor antagonists: comparative tolerability and safety. Drug Saf . 1994; 10:350-80. [PubMed 7913608]

581. Wasserfallen JB, Leuenberger P, Pécoud A. Effect of cetirizine, a new H1 antihistamine, on the early and late allergic reactions in a bronchial provocation test with allergen. J Allergy Clin Immunol . 1993; 91:1189-97. [PubMed 8099593]

582. Klausner MA. Dear doctor letter regarding important drug warning of Hismanal® (astemizole). Titusville, NJ: Janssen Phrarmaceutica; 1998 Feb.

583. Spencer CM, Faulds D, Peters DH. Cetirizine: a reappraisal of its pharmacological properties and therapeutic use in selected allergic disorders. Drugs 1993; 46:1055-80.

584. Pfizer Laboratories. Zyrtec® (cetirizine hydrochloride) tablets product monograph. New York, NY: Undated.

585. Novartis. Tavist® (clemastine fumarate) tablets prescribing information. In: Physicians' desk reference for nonprescription drugs. 52nd edition. Montvale NJ: Medical Economics Company Inc; 1998:708-9.

586. Warner-Lambert. Actifed® cold and allergy tablets prescribing information. In: Physicians' desk reference for nonprescription drugs. 52nd edition. Montvale NJ: Medical Economics Company Inc; 1998:798.

587. Schering Corp. Claritin-D 12 Hour (loratadine and pseudoephedrine sulfate) extended-release tablets prescribing information. Kenilworth, NJ; 1997 Feb.

588. Schering Corp. Claritin-D 24 Hour (loratadine and pseudoephedrine sulfate) extended-release tablets prescribing information. In: Physicians' desk reference. 52nd ed. Montvale NJ: Medical Economics Company Inc; 1998 (Suppl A):A278-80.

589. Okerholm RA, Weiner DL, Hook RH et al. Bioavailability of terfenadine in man. Biopharm Drug Dispos . 1981; 2:185-90. [PubMed 6113858]

590. Garteiz DA, Hook RH, Walker BJ et al. Pharmacokinetics and biotransformation studies of terfenadine in man. Arzneimittelforschung . 1982; 32:1185-90. [PubMed 6817765]

591. Cook CE, Williams DL, Myers M et al. Radioimmunoassay for terfenadine in human plasma. J Pharm Sci . 1980; 69:1419-23. [PubMed 6109770]

592. Munro NL, Robinson RE (Merrell Dow, Cincinnati, OH): Personal communication on terfenadine 4:00; 1985 Jul 19.

593. Reviewers' comments (personal observations) on terfenadine 4:00.

594. Marion Merrell Dow. Seldane® (terfenadine) tablets prescribing information. Kansas City, MO. 1993 Jan.

595. Rolf CN. Dear doctor letter regarding important drug warning of Seldane. Cincinnati, OH: Marion Merrell Dow; 1990 Aug 6.

596. Hoechst Marion Roussel. Seldane-D® (terfenadine and pseudoephedrine hydrochloride) extended-release tablets prescribing information. Kansas City, MO; 1997 Sep.

597. Marion Merrell Dow, Kansas City, MO: Personal communication on terfenadine 4:00.

598. Eller MG, Okerholm RA. Pharmacokinetic interaction between terfenadine and ketoconazole. Clin Pharmacol Ther . 1991; 49:130.

599. Cantilena LR Jr. Torsades de pointes occurring in association with terfenadine use. JAMA . 1991; 266:2376.

600. Torsades de pointes. In: Braunwald E, ed. Heart disease: a textbook of cardiovascular medicine. Philadelphia: WB Saunders; 1992:707-8.

601. Stratmann HG, Kennedy HL. Torsades de pointes associated with drugs and toxins: recognition and management. Am Heart . 1987; 113:1470-82.

602. Perticone F, Adinolfi L, Bonaduce D. Efficacy of magnesium sulfate in the treatment of torsade de pointes. Am Heart J . 1986; 112:847-9. [PubMed 3766386]

603. Rogiers P, Vermeier W, Kesteloot H et al. Effect of infusion of magnesium sulfate during atrial pacing on ECG intervals, serum electrolytes, and blood pressure. Am Heart J . 1989; 117:1278-83. [PubMed 2729056]

604. Eller MG, Okerholm RA. Effect of cimetidine on terfenadine and terfenadine metabolite pharmacokinetics. Pharm Res . 1991; 8(Suppl 10):297.

605. Antihistamines, nonsedating/azole antifungal agents. In: Tatro DS, Olin BR, Hebel SK, eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1995(July):110a.

606. Antihistamines, nonsedating/macrolide antibiotics. In: Tatro DS, Olin BR, Hebel SK, eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1997(October):110d.

607. Hoechst Marion Roussel. Seldane® (terfenadine) 60-mg tablets prescribing information. Kansas City, MO; 1997 Sep.

608. Azithromycin (Zithromax) interactions: terfenadine (Seldane). In: Hansten PD, Horn JR. Drug interactions and updates. Vancouver, WA: Applied Therapeutics, Inc; 1994:743-4.

609. Muro Pharmaceutical Inc. Dynabac® (dirithromycin tablets) prescribing information. Tewksbury, MA: 1999 Oct 11.

610. Honig P, Wortham D, Zamani K et al. Effect of erythromycin, clarithromycin and azithromycin on the pharmacokinetics of terfenadine. Clin Pharmacol Ther . 1993; 53:161.

611. Harris S, Hilligoss DM, Colangelo PM et al. Azithromycin and terfenadine: lack of drug interaction. Clin Pharmacol Ther . 1995; 58:310-5. [PubMed 7554704]

612. Itraconazole (Sporanox) interactions: terfenadine (Seldane). In: Hansten PD, Horn JR. Drug interactions and updates. Vancouver, WA: Applied Therapeutics, Inc; 1994:750.

613. Clarithromycin (Biaxin) interactions: terfenadine (Seldane). In Hansten PD, Horn JR. Drug interactions and updates. Vancouver, WA: Applied Therapeutics, Inc; 1994:747.

614. Janssen Pharmaceutica, Titusville, NJ: Personal communication on terfenadine 4:00.

615. Hoechst Marion Roussel, Kansas City, MO: Personal communication on terfenadine 4:00.

616. Anon. Grapefruit juice interactions with drugs. Med Lett Drugs Ther . 1995; 37:73-4. [PubMed 7630329]

617. Honig P, Wortham D, Lazarev A et al. Pharmacokinetics and cardiac effects of terfenadine in poor metabolizers receiving concomitant grapefruit juice. Clin Pharmacol Ther . 1995; 57:185.

618. Bailey DG, Spence JD, Munoz C et al. Interaction of citrus juices with felodipine and nifedipine. Lancet . 1991; 337:268-9. [PubMed 1671113]

619. Ducharme MP, Warbasse LH, Edwards DJ. Disposition of intravenous and oral cyclosporine after administration with grapefruit juice. Clin Pharmacol Ther . 1995; 57:485-91. [PubMed 7768070]

620. Cyclosporine/food (grapefruit juice). In: Tatro DS, Olin BR, Hebel SK eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1996(July):233b.

621. Midazolam (Versed) interactions: grapefruit juice. In: Hansten PD, Horn JR. Drug interactions and updates. Vancouver, WA: Applied Therapeutics, Inc; 1996:932.

622. Proppe DG, Hoch OD, McLean AJ et al. Influence of chronic ingestion of grapefruit juice on steady-state blood concentrations of cyclosporine A in renal transplant patients with stable graft function. Br J Clin Pharmacol . 1995; 39:337-8. [PubMedCentral][PubMed 7619679]

623. Kupferschmidt HHT, Ha HR, Ziegler WH et al. Interaction between grapefruit juice and midazolam in humans. Clin Pharmacol Ther . 1995; 58:20-8. [PubMed 7628179]

624. Ameer B, Weintraub RA, Johnson JV et al. Flavanone absorption after naringin, hesperidin, and citrus administration. Clin Pharmacol Ther . 1996; 60:34-40. [PubMed 8689809]

625. Yee GC, Stanley DL, Pessa LJ et al. Effect of grapefruit juice on blood cyclosporin concentration. Lancet . 1995; 345:955-6. [PubMed 7715295]

626. Hollander AAMJ, van Rooij J, Lentjes EGWM et al. The effect of grapefruit juice on cyclosporine and prednisone metabolism in transplant patients. Clin Pharmacol Ther . 1995; 57:318-24. [PubMed 7697949]

627. Bailey DG, Arnold JMO, Spence JD. Grapefruit juice and drugs: how significant is the interaction? Clin Pharmacokinet . 1994; 26:91-8.

628. Merkel U, Sigusch H, Hoffmann A. Grapefruit juice inhibits 7-hydroxylation of coumarin in healthy volunteers. Eur J Clin Pharmacol . 1994; 46:175-7. [PubMed 8039540]

629. Soons PA, Vogels BAPM, Roosemalen MCM et al. Grapefruit juice and cimetidine inhibit stereoselective metabolism of nitrendipine in humans. Clin Pharmacol Ther . 1991; 50:394-403. [PubMed 1914375]

630. Fuhr U, Klittich K, Staib AH. Inhibitory effect of grapefruit juice and its bitter principal, naringenin, on CYP1A2 dependent metabolism of caffeine in man. Br J Clin Pharmacol . 1993; 35:431-6. [PubMedCentral][PubMed 8485024]

631. Campana C, Regazzi MB, Buggia I et al. Clinically significant drug interactions with cyclosporin: an update. Clin Pharmacokinet . 1996; 30:141-179. [PubMed 8906896]

632. Pfizer, New York, NY: Personal communication on terfenadine 4:00.

633. Goldberg MJ, De Sante K, Cerimele B et al. Effect of dirithromycin on terfenadine pharmacokinetics and Qtc in healthy men. Clin Pharmacol Ther . 1995; 57:176.

634. Dista. Ilotycin® Gluceptate (erythromycin gluceptate) prescribing information. In: Physicians' desk reference. 48th ed. Montvale, NJ: Medical Economics Company Inc; 1994:871-2.

635. Schering Corp. Claritin® (loratadine) tablets, syrup and rapidly disintegrating tablets prescribing information. Kenilworth, NJ; 1997 Jan.

636. Edwards DJ, Bernier SM. Naringin and naringenin are not the primary CYPTS inhibitors in grapefruit juice. Life Sci . 1996; 59:1025-30. [PubMed 8809221]

637. Lundahl J, Regardh CG, Edgar B et al. Relationship between time of intake of grapefruit juice and its effect on pharmacokinetics and pharmacodynamics of felodipine in healthy subjects. Eur J Clin Pharmacol . 1995; 49:61-7. [PubMed 8751023]

638. Hoechst Marion Roussel. Allegra® (fexofenadine hydrochloride) capsules prescribing information (dated 1996 Oct). In: Physicians' desk reference. 49th ed. Montvale, NJ: Medical Economics Company Inc; 1997 (Suppl A):A37-8.

639. Roche, Nutley, NJ: Personal communication on terfenadine 4:00.

640. Pfizer. Zithromax® (azithromycin) tablets, capsules, and for oral suspension prescribing information. In: Physicians' desk reference. 51st ed. Montvale, NJ: Medical Economics Company Inc; 1997(Suppl A):A255-9.

641. Pfizer. Zoloft® (sertraline) tablets prescribing information. New York, NY; 1997 Nov 4.

642. Nonsedating antihistamines/histamine H2 antagonists. In: Tatro DS, Olin BR, Hebel SK eds. Drug interaction facts. St. Louis: JB Lippincott Co; 1997 (Oct):110b.

643. Rankin AC. Non-sedating antihistamines and cardiac arrhythmia. Lancet . 1997; 350:1115-6. [PubMed 9343494]

644. Ng PW, Chan WK, Chan TYK. Torsade de pointes during concomitant use of terfenadine and cimetidine. Aust N Z J Med . 1996; 26:120. [PubMed 8775544]

645. Lindquist M, Edwards IR. Risks of non-sedating antihistamines. Lancet . 1997; 349:1322. [PubMed 9142080]

646. Clark S. Dangers of non-sedating antihistamines. Lancet . 1997; 349:1268. [PubMed 9142059]

647. Pfizer Inc. Zoloft® (sertraline hydrochloride) tablets prescribing information. New York; 1997 Oct.

648. Hoechst Marion Roussel, Kansas City, MO: Personal communication on fexofenadine 4:00.

649. Spence D. Drug interactions with grapefruit: whose responsibility is it to warn the public? Clin Pharmacol Ther . 1997; 61:395-400.

650. Haria M, Fitton A, Peters DH. Loratadine. A reappraisal of its pharmacological properties and therapeutic use in allergic disorders. Drugs . 1994; 48:617-37. [PubMed 7528133]

651. Hilbert J, Radwanski E, Weglein R et al. Pharmacokinetics and dose proportionality of loratadine. J Clin Pharmacol . 1987; 27:694-8. [PubMed 2960701]

652. Anon. Loratadine—a new antihistamine. Med Lett Drugs Ther . 1993; 35:71-2. [PubMed 8336639]

653. Hilbert J, Moritzen V, Parks A et al. The pharmacokinetics of loratadine in normal geriatric volunteers. J Int Med Res . 1988; 16:50-60. [PubMed 2965043]

654. Hilbert JM, Matzke GR, Radwanski E et al. Loratadine pharmacokinetics in renal impairment. J Allergy Clin Immunol . 1987; 79:206.

655. Marion Merrell Dow. Seldane® (terfenadine) tablets prescribing information. Cincinnati, OH; 1990 Jul.

656. Merck. Crixivan® (indinavir) capsules prescribing information (dated 1998 Feb). In: Physicians' desk reference. 52nd ed. Montvale, NJ: Medical Economics Company Inc; 1998(Suppl A):A205-8.

657. Abbott Laboratories. Norvir® (ritonavir) capsules and oral solution prescribing information (dated 1997 Mar). In: Physicians' desk reference. 52nd ed. Montvale, NJ: Medical Economics Company Inc; 1998:459-64.

658. Glaxo Wellcome. Raxar® (grepafloxacin hydrochloride) tablets prescribing information. Research Triangle Park, NC; 1997 Nov.

659. Janssen. Dear health care professional letter regarding withdrawal of Hismanal® (astemizole). Titusville, NJ: 1999 July 18.

660. Anon. Janssen Pharmaceutica announces the withdrawal of Hismanal from the market. FDA Talk Paper. Rockville, MD: Food and Drug Administration; 1999 Jun 21.

661. Dinndorf PA, McCabe MA, Frierdich S. Risk of abuse of diphenhydramine in children and adolescents with chronic illnesses. J Pediatrics . 1998; 133:293-5.

662. Watemberg NM, Roth KS, Alehan FK et al. Central anticholinergic syndrome on therapeutic doses of cyproheptadine. Pediatrics . 1999; 103:158-60. [PubMed 9917456]

663. Carr RA, Edmonds A, Shi H et al. Steady-state pharmacokinetics and electrocardiographic pharmacodynamics of clarithromycin and loratadine after individual or concomitant administration. Antimicrobial Agents Chemother . 1998; 42:1176-1180.

664. Rhone-Poulenc Rorer. Synercid® I.V. (quinupristin/dalfopristin) for injection prescribing information. Collegeville, PA: 1999 Jul.

665. ECR Pharma. Lodrane® Allergy (brompheniramine maleate) capsules prescribing information. Richmond, VA; 1999 Apr.

666. Biovail Pharmaceuticals Inc. Rondec®-DM (brompheniramine maleate, pseudoephedrine hydrochloride, dextromethorphan hydrobromide) syrup prescribing information. Morrisville, NC; 2001 May.

667. Biovail Pharmaceuticals Inc. Rondec® (carbinoxamine maleate and pseudoephedrine hydrochloride) oral drops prescribing information. Morrisville, NC; 2001 May.

668. Biovail Pharmaceuticals Inc. Rondec® (brompheniramine maleate and pseudoephedrine hydrochloride) syrup prescribing information. Morrisville, NC; 2001 May.

669. McClellan K, Jarvis B. Desloratadine. Drugs . 2001; 61:789-96. [PubMed 11398910]

670. Schering Corporation. Clarinex® (desloratadine) tablets prescribing information. Kenilworth, NJ; 2002 Feb.

671. Agrawal DK. Pharmacology and clinical efficacy of desloratadine as an anti-allergic and anti-inflammatory drug. Expert Opin Investig Drugs . 2001; 10:547-60. [PubMed 11424898]

672. Food and Drug Administration. Labeling of diphenhydramine-containing drug products for over-the-counter human use. 21 CFR Parts 336, 338, 341, 348. Final rule. [Docket No. 97N-0128] Fed Regist . 2002; 67:72555-9.

673. Gottwald MD, Gidal BE, Flaherty J. Parkinson's Disease. In: Koda-Kimble MA, Young LY eds. Applied therapeutics: the clinical use of drugs. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2001:51-1—51-27.

674. Young, R. Update on Parkinson's disease. Am Fam Physician . 1999; 59:2155-69. [PubMed 10221302]

675. Nelson MV, Berchou RC, LeWitt PA. Parkinson's Disease. In: DiPiro JT, Talbert RL, Yee GC et al., eds. Pharmacotherapy: a pathophysiologic approach. 5th ed. Stamford: The McGraw-Hill Companies, Inc.; 2002:1089-102.

676. Crimson ML, Dorson PG. Schizophrenia. In DiPiro JT, Talbert RL, Yee GG et al., eds. Pharmacotherapy: a pathophysiologic approach. 5th ed. Stanford: The McGraw-Hill Companies, Inc.; 2002:1219-42.

677. Pamlab, LLC. Palgic® (4 mg carbinoxamine maleate) prescribing information. Covington, IA; 2006 Jun.

678. Food and Drug Administration. Over-the-counter drug products intended for oral ingestion that contain alcohol. 21 CFR Part 328. Final Rule. [Docket No. 93N-0107] Fed Regist. 1995; 60:13590-5.

679. Food and Drug Administration. Cold, cough, allergy, bronchodilator, and antiasthmatic drug products for over-the-counter human use. 21 CFR Part 341. Final Rule. [Docket No. 76N-052G] Fed Regist. 2002; 67:78158-72.

680. Kris MG, Hesketh PJ, Somerfield MR et al. American Society of Clinical Oncology guideline for antiemetics in oncology: update 2006. J Clin Oncol . 2006; 24:1-16. [PubMed 16330665]

681. de Blic J, Wahn U, Billard E et al. Levocetirizine in children: evidenced efficacy and safety in a 6-week randomized seasonal allergic rhinitis trial. Pediatr Allergy Immunol . 2005; 16:267-75. [PubMed 15853959]

682. Potter PC for the Study Group. Levocetirizine is effective for symptom relief including nasal congestion in adolescent and adult (PAR) sensitized to house dust mites. Allergy . 2003; 58:893-9. [PubMed 12911418]

683. Kapp A, Pichler WJ. Levocetirizine is an effective treatment in patients suffering from chronic idiopathic urticaria: a randomized, double-blind, placebo-controlled, parallel, multicenter study. Int J Dermatol . 2006; 45:469-74. [PubMed 16650180]

684. Nettis E, Colanardi MC, Barra L et al. Levocetirizine in the treatment of chronic idiopathic urticaria: a randomized, double-blind, placebo-controlled study. Br J Dermatol. 2006; 154:533-8. [PubMed 16445787]

685. UCB Inc. Xyzal (levocetirizine dihydrochloride) tablets prescribing information. 2007 May. From UCB web site. [Web]

686. Benedetti MS, Plisnier M, Kaise J et al. Absorption, distribution, metabolism, and excretion of [14C] levocetirizine, the R enantiomer of cetirizine, in healthy volunteers. Eur J Clin Pharmacol . 2001; 57:571-82. [PubMed 11758635]

687. Layton D, Wilton L, Boshier A et al. Comparison of the risk of drowsiness and sedation between levocetirizine and desloratadine: a prescription-event monitoring study in England. Drug Saf . 2006; 29:897-909. [PubMed 16970513]

693. Srinivasan A, Budnitz D, Shehab N et al. Infant deaths associated with cough and cold medications—two states, 2005. MMWR Morb Mortal Wkly Rep . 2007; 56:1-4. [PubMed 17218934]

694. Food and Drug Administration. Cough and cold medications in children less than two years of age. Rockville, MD; 2007 Jan 12. From FDA website. [Web]

695. Anon. Drugs for allergic disorders. Treat Guidel Med Lett . 2007; 5:71-80.

696. Food and Drug Administration. Carbinoxamine products: Enforcement action dates (Docket No. 2006N-0229). Fed Regist. 2006; 71:33462-5.

697. Food and Drug Administration. Questions and answers about unapproved drugs and FDA's enforcement action against carbinoxamine products. Rockville, MD; 2006 Jun. From FDA website. [Web]

698. Anon. Makers pull cold medicines sold for infants. CNN News, 2007 Oct 11. From CNN.com website. [Web]

699. Food and Drug Administration. FDA news: FDA releases recommendations regarding use of over-the-counter cough and cold products. Rockville, MD; 2008 Jan 17. From the FDA web site. [Web]

700. Richwine L. U.S. panel against cold drugs for kids under 6. Reuters, 2007 Oct 19. From Reuters website. [Web]

701. Food and Drug Administration. Over the counter cough and cold medications. Rockville, MD; October 2008. From FDA website. [Web]

702. Food and Drug Administration. FDA statement: FDA statement following CHPA's announcement on nonprescription over-the-counter cough and cold medicines in children. 2008 Oct 8. From the FDA website. [Web]

703. Consumer Healthcare Products Association. Statement from CHPA on the voluntary label updates to oral OTC children's cough and cold medicines. 2008 Oct 7. [Web]

704. Heavey S. Don't use cold drugs in kids under 4: manufacturers. Reuters, 2008 Oct 8. From Reuters website. [Web]

705. Duchesnay USA, Inc. Diclegis® (doxylamine succinate and pyridoxine hydrochloride) delayed-release tablets prescribing information. Bryn Mawr, PA; 2013 Apr.

706. Duchesnay USA, Inc. Bonjesta® (doxylamine succinate and pyridoxine hydrochloride) extended-release tablets prescribing information. Bryn Mawr, PA; 2016 Nov.

707. US Food and Drug Administration. Center for Drug Evaluation and Research. Application number 021876Orig1s000: Summary Review. From FDA website. Accessed 2017 Apr. [Web]

708. Koren G, Clark S, Hankins GD et al. Effectiveness of delayed-release doxylamine and pyridoxine for nausea and vomiting of pregnancy: a randomized placebo controlled trial. Am J Obstet Gynecol . 2010; 203:571.e1-7. [PubMed 20843504]

709. US Department of Health and Human Services. Federal Register . Determination that Bendectin was not withdrawn from sale for reasons of safety or effectiveness. 1999; 64:43190-1.

710. . American College of Obstetricians and Gynecologists. Practice Bulletin No. 153: Nausea and vomiting of pregnancy. Obstet Gynecol . 2015; 126:e12-24. [PubMed 26287788]

711. McKeigue PM, Lamm SH, Linn S et al. Bendectin and birth defects: I. A meta-analysis of the epidemiologic studies. Teratology . 1994; 50:27-37. [PubMed 7974252]

712. Einarson TR, Leeder JS, Koren G. A method for meta-analysis of epidemiological studies. Drug Intell Clin Pharm . 1988; 22:813-24. [PubMed 3229352]