Administration 
Promethazine hydrochloride may be administered orally, rectally, or by deep IM injection. Promethazine hydrochloride also is administered by IV injection. However, because IV administration of the drug has been associated with severe tissue injury, including gangrene requiring amputation, the US Food and Drug Administration (FDA) states that deep IM injection is the preferred method for administration of promethazine hydrochloride injections.139,140 (See Cautions: Precautions and Contraindications.) If IV administration of promethazine hydrochloride is required, FDA states that the drug should be administered through the tubing of an IV infusion set that is known to be correctly functioning; FDA also states that the maximum rate of IV administration is 25 mg/minute, and the maximum concentration of the injection is 25 mg/mL.139 If the patient complains of pain at the injection site during presumed IV injection of the drug, the injection should immediately be stopped, and the possibility of intra-arterial placement of the needle or perivascular extravasation should be evaluated.102,139 Promethazine hydrochloride injection is commercially available in 2 strengths: 25 mg/mL and 50 mg/mL.102,139 FDA states that the preparation containing 50 mg/mL is for IM injection only ; the preparation containing 25 mg/mL may be administered by IM or IV injection.139
Because of the risk of severe tissue injury and amputations if promethazine hydrochloride is inadvertently administered intra-arterially or if extravasation were to occur, some medication safety experts (e.g., the Institute for Safe Medication Practices [ISMP]) recommend that parenteral administration of the drug be avoided and replaced by safer alternative therapies (e.g., a type 3 serotonin [5-HT3] receptor antagonist such as ondansetron).145
Subcutaneous or intra-arterial injection of promethazine hydrochloride is contraindicated. 139,140
Promethazine hydrochloride injections should be inspected visually for particulate matter and discoloration prior to administration whenever solution and container permit.102 The injection should be discarded if the solution is discolored or contains a precipitate.
Dosage
Dosages of promethazine hydrochloride by the various routes of administration are identical.
For routine, preoperative or postoperative sedation or as an adjunct to analgesics for the control of pain, the usual adult dose of promethazine hydrochloride is 25-50 mg; children may receive 12.5-25 mg or 0.5-1.1 mg/kg. When promethazine is used as an adjunct to opiate analgesics, dosage of the analgesic should usually be reduced.
In obstetrics, 50 mg of promethazine hydrochloride may be given to provide sedation during the early stage of labor. When labor is established, 25-75 mg may be given with a reduced therapeutic dose of an opiate agonist. Although additional doses are usually not required, the manufacturers state that 25- to 50-mg doses of promethazine may be repeated once or twice at 4-hour intervals if necessary. The maximum total dosage of promethazine during a 24-hour period of labor is 100 mg.
For the prevention and management of nausea and vomiting, the usual adult dose of promethazine hydrochloride is 12.5-25 mg; additional doses of 12.5-25 mg may be given every 4 hours if necessary. Children have been given 0.25-0.5 mg/kg or 7.5-15 mg/m2 4-6 times daily for the treatment of nausea and vomiting. (See Cautions: Pediatric Precautions.)
Adverse Effects
Promethazine has adverse effects similar to those of other antihistamines and shares the toxic potentials of the phenothiazines; the usual precautions of antihistamine and phenothiazine therapy should be observed. (See Cautions in the Antihistamines General Statement 4:00 and in the Phenothiazines General Statement 28:16.08.24.) Although the risk of adverse reactions (e.g., blood dyscrasias, hepatotoxicity, reactivation of psychotic processes, tachycardia, cardiac arrest, endocrine disturbances, dermatologic disorders, ocular changes, hypersensitivity reactions) that have occurred during long-term administration of antipsychotic phenothiazines appears to be minimal, the possibility that such reactions could occur with prolonged administration of promethazine should be considered.
Adverse anticholinergic effects of promethazine include dryness of the mouth, blurring of vision and, rarely, dizziness. Confusion and disorientation also may occur. Extrapyramidal reactions may occur102,115 with high doses and usually subside with dosage reduction.102 Lassitude, fatigue, incoordination, tinnitus, diplopia, oculogyric crises, insomnia, excitation, nervousness, euphoria, hysteria, tremors, seizures, abnormal movements,100,117 nightmares,100 delirium,100 agitation,100,115 hallucinations,100 torticollis,100 tongue protrusion,100 oversedation,115 dystonic reactions,115 and catatonic-like states have been reported.100,102 Restlessness, akathisia, and, occasionally, marked irregular respiration have occurred. Neuroleptic malignant syndrome (NMS) also may occur.100,115,117 Patients with pain who have received inadequate or no analgesia have developed athetoid-like movements of the upper extremities following parenteral administration of promethazine. These symptoms usually disappeared when the pain was controlled.
Leukopenia, thrombocytopenia, thrombocytopenic purpura, and agranulocytosis have been reported in patients receiving promethazine.100,102
Tachycardia, bradycardia, increased or decreased blood pressure, and faintness have occurred in patients receiving promethazine.100,102,117 Although rapid IV administration of promethazine may produce a transient fall in blood pressure, blood pressure usually is maintained or slightly elevated when the drug is given slowly. Venous thrombosis at the injection site also has been reported.102
Promethazine has been associated with obstructive jaundice, which usually was reversible following discontinuance of the drug.102 Cholestatic jaundice, nausea, and vomiting have been reported in patients receiving promethazine.100,102 Photosensitivity has been reported and may be a contraindication to further promethazine therapy. Urticaria, dermatitis, asthma, dermatologic reactions, and angioedema also have occurred.100,102,115,117 Nasal stuffiness, respiratory depression (may be fatal), cardiac arrest, and apnea (may be fatal) also may occur.100,102,115,116,117
Local Reactions Associated with Promethazine Hydrochloride Injection
Severe chemical irritation and damage to tissues (e.g., burning, pain, erythema, swelling, severe spasm of distal vessels, thrombophlebitis, venous thrombosis, phlebitis, abscesses, tissue necrosis, gangrene) may occur with administration of promethazine injection regardless of the route of administration.30,31,102,139,140,141,142,143,144 Such irritation and damage also may result from perivascular extravasation, unintentional intra-arterial injection, and intraneuronal or perineuronal infiltration.30,31,102,139,140,141,142,143,144 Parenteral administration of promethazine may produce nerve damage (ranging from temporary sensory loss to palsies and paralysis) while injection near or into a nerve may result in permanent tissue damage.102,139 In some cases, surgical intervention (e.g., fasciotomy, skin graft, amputation) may be needed.102,139,140,141,144 (See Dosage and Administration: Administration and see also Cautions: Precautions and Contraindications.)
Precautions and Contraindications
Promethazine has adverse effects similar to those of other antihistamines and shares the toxic potentials of the phenothiazines; the usual precautions of antihistamine and phenothiazine therapy should be observed. (See Cautions: Precautions and Contraindications in the Antihistamines General Statement 4:00 and in the Phenothiazines General Statement 28:16.08.24.)
Ambulatory patients should be warned that promethazine may impair their ability to perform hazardous tasks requiring mental alertness or physical coordination such as operating machinery or driving a motor vehicle. It should be kept in mind that the antiemetic effect of promethazine may obscure signs of overdosage of other drugs or of symptoms of conditions such as intestinal obstruction or brain tumor, and thereby interfere with diagnosis.
Promethazine should be used with caution in patients with cardiovascular disease or impaired liver function or patients who are having an asthmatic attack. Some manufacturers state that promethazine should be used cautiously in individuals with peptic ulcer. Some manufacturers also state that the drug should be used with caution in patients with acute or chronic respiratory impairment, particularly children, because the cough reflex may be suppressed. Promethazine should be used with caution, if at all, in patients with sleep apnea.100,105,110 (See Cautions: Pediatric Precautions.)
Some commercially available formulations of promethazine hydrochloride contain sulfites that may cause allergic-type reactions, including anaphylaxis and life-threatening or less severe asthmatic episodes, in certain susceptible individuals. The overall prevalence of sulfite sensitivity in the general population is unknown but probably low; such sensitivity appears to occur more frequently in asthmatic than in nonasthmatic individuals.
Because IV administration of the drug has been associated with severe tissue injury, including gangrene requiring amputation, the US Food and Drug Administration (FDA) states that deep IM injection is the preferred method for administration of promethazine hydrochloride injections.139,140 If IV administration of promethazine hydrochloride is required, extreme care should be exercised to avoid extravasation or inadvertent intra-arterial injection. (See Dosage and Administration: Administration and see Local Reactions Associated with Promethazine Hydrochloride Injection under Cautions: Adverse Effects.) If the patient complains of pain at the injection site during presumed IV injection of the drug, the injection should immediately be stopped, and the possibility of intra-arterial placement of the needle or perivascular extravasation should be evaluated.102,139 Clinicians should be alert for signs and symptoms of potential tissue injury, including burning or pain at the site of injection, phlebitis, swelling, and blistering, and patients should be informed that adverse effects may occur immediately (i.e., while receiving the injection) or may develop hours to days after an injection of promethazine.139 Although there are no proven successful treatment regimens for the management of extravasation or inadvertent intra-arterial injection of promethazine, sympathetic block and administration of heparin are commonly employed during the acute management.102
Because of the risk of severe tissue injury and amputations if promethazine hydrochloride is inadvertently administered intra-arterially or if extravasation were to occur, some medication safety experts (e.g., the Institute for Safe Medication Practices [ISMP]) recommend that parenteral administration of the drug be avoided and replaced by safer alternative therapies (e.g., a type 3 serotonin [5-HT3] receptor antagonist such as ondansetron).145
FDA states that subcutaneous or intra-arterial administration of promethazine hydrochloride is contraindicated.139,140 Promethazine hydrochloride should not be administered intra-arterially, because chemical irritation may be severe and cause severe arteriospasm, possibly resulting in impairment of circulation and gangrene requiring amputation.102 Since promethazine discolors blood on contact, aspiration of dark blood at the site of injection does not rule out the possibility of intra-arterial placement of the needle.102
Promethazine is contraindicated in patients who have exhibited hypersensitivity or idiosyncrasy to promethazine or other phenothiazines.100,102,117 Promethazine also is contraindicated in pediatric patients younger than 2 years of age because of risk of developing potentially fatal respiratory depression. 100,102,114,115,116,117 (See Cautions: Pediatric Precautions.) In addition, the drug is contraindicated in patients who have received large doses of other CNS depressants and/or who are comatose. The manufacturers state that the drug is contraindicated for use in the treatment of lower respiratory tract symptoms (e.g., asthma).100,117 There is some evidence that epileptic patients may experience increased severity of seizures if treated with promethazine, and the drug may be contraindicated in these patients. Since increases in blood pressure may occur, promethazine should be administered with extreme caution, if at all, to patients in hypertensive crisis. Some manufacturers state that promethazine also is contraindicated in patients with bone marrow depression, angle-closure glaucoma, prostatic hypertrophy, stenosing peptic ulcer, pyloroduodenal obstruction, or bladder neck obstruction, although others state that the drug may be used with caution in such patients.100,102,113,117 Some experts do not recommend administering promethazine to pediatric patients who are vomiting, unless the vomiting is prolonged and there is a known cause. (See Cautions: Pediatric Precautions.)117
Pediatric Precautions
Because respiratory depression (sometimes fatal) has been reported in pediatric patients younger than 2 years of age receiving a wide range of weight-adjusted doses of promethazine during postmarketing surveillance, the drug is contraindicated in pediatric patients younger than 2 years of age.100,102,114,115,116,117
Promethazine should be administered with caution in children 2 years of age and older because of possible respiratory depression and/or apnea that may be fatal.100,102,114,115,116,117 The lowest effective dose of the drug should be used.100,102,114 Concomitant use of promethazine with other respiratory depressant drugs should be avoided.100,102,114
Children receiving promethazine should be supervised closely while performing hazardous activities such as bike riding. Adults responsible for the supervision of a child receiving promethazine should be warned that children may be at increased risk for experiencing CNS stimulant effects with antihistamines. Promethazine should not be used in vomiting of unknown etiology in children. The drug should not be used in acutely ill or dehydrated children or children with acute infections, since these patients have an increased susceptibility to dystonias. Use of promethazine also should be avoided in children with signs and symptoms that suggest Reye's syndrome, since the potential extrapyramidal effects produced by the drug may obscure the diagnosis of or be confused with the CNS signs and symptoms of this condition, and in children with signs and symptoms of other hepatic disease.102 Because promethazine may cause marked drowsiness that may be potentiated by other CNS depressants (e.g., sedatives, tranquilizers), promethazine should be used in children receiving one of these drugs only under the direction of a physician. Promethazine should not be used in children with asthma, liver disease, a seizure disorder, or glaucoma unless otherwise directed by a clinician.
Excessively high dosages of promethazine have caused sudden death in pediatric patients,100,102 although sleep apnea and sudden infant death syndrome (SIDS) have been reported in a number of infants and young children who were receiving usual dosages of promethazine105,109 or trimeprazine (no longer commercially available in the US).104,105,108 The relationship to the drugs and possible mechanism(s) of such effects have not been elucidated.105,106,107,108,109 In one study, the number but not the duration of central apneas during sleep was increased and obstructive apnea during sleep (accompanied by decreased heart rate and arterial oxygen pressure) developed in 4 healthy infants who were receiving 1 mg/kg of promethazine hydrochloride daily for 3 days.109 Promethazine should be used with caution in children with a history of sleep apnea, those with a family history of SIDS, and those who are less prone than usual to spontaneous arousal from sleep.100,109,110
Geriatric Precautions
Clinical studies of promethazine did not include sufficient numbers of patients 65 years of age and older to determine whether geriatric patients respond differently than younger patients.100 Although clinical experience generally has not revealed age-related differences in response to the drug, care should be taken in dosage selection of promethazine.100 Because of increased risk of sedative effects and confusion (associated with promethazine) and the greater frequency of decreased hepatic, renal, and/or cardiac function and of concomitant disease and drug therapy in geriatric patients, the manufacturers suggest that patients in this age group receive initial dosages of the drug in the lower end of the usual range.100
Mutagenicity and Carcinogenicity
Long-term animal studies to determine the carcinogenic potential of promethazine have not been performed to date.100,102,113 There was no evidence of promethazine-induced mutagenesis in the Ames microbial mutagen test.100,102,113 There are no human or other animal data concerning the carcinogenic or mutagenic potentials of the drug.100,102,113 For information on the carcinogenic potential of phenothiazines, see Cautions: Carcinogenicity, in the Phenothiazines General Statement 28:16.08.24.
Pregnancy, Fertility, and Lactation
Pregnancy
Safe use of promethazine during pregnancy (except during labor) with respect to possible adverse effects on fetal development has not been established. Although there are no adequate and controlled studies to date in humans, promethazine has not been shown to be teratogenic in rats receiving oral dosages of 6.25-12.5 mg/kg daily (about 2.1-4.2 times the maximum recommended human dosage, depending on the use of the drug). The drug has been shown to produce fetal mortality in rats receiving intraperitoneal dosages of 25 mg/kg daily.100 Antihistamines, including promethazine, have been fetocidal in rodents, but the pharmacologic effects of histamine in rodents differ from those in humans. Promethazine should be used during pregnancy only when the potential benefits justify the possible risks to the fetus.
Fertility
There are no animal or human data concerning the effect of promethazine on fertility.100
Lactation
It is not known whether promethazine is distributed into milk. Because many drugs are distributed in human milk and because of the potential for serious adverse reactions to promethazine in nursing infants if it were distributed, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.100,102
Laboratory Test Interferences
Promethazine may interfere with several immunologic urinary pregnancy tests. The drug may elicit a false-positive Gravindex® test and false-negative Prepurex® and Dap® test. Promethazine may interfere with blood grouping in the ABO system. The drug substantially alters the flare response in intradermal allergen tests.
Acute Toxicity
Manifestations
In adults, overdosage of promethazine may range from mild depression of the CNS and cardiovascular system to profound hypotension, respiratory depression, seizures, deep sleep, unconsciousness, and sudden death.100 Hyperreflexia, hypertonia, ataxia, athetosis, and extensor-plantar reflexes (Babinski reflex) also may occur.100 In children, a paradoxical reaction characterized by hyperexcitability, abnormal movements, nightmares, and respiratory depression may occur. A 12-year-old patient who had taken 200 mg of the drug exhibited numbness and pain in the left leg, tactile hallucinations, extreme hyperesthesia and hyperalgesia, and sinus tachycardia.
Treatment
For information on the treatment of promethazine overdosage, see Acute Toxicity: Treatment in the Phenothiazines General Statement 28:16.08.24.
Pharmacology
Promethazine is a phenothiazine derivative with potent sedative properties. Although the drug can produce either CNS stimulation or CNS depression, CNS depression manifested by sedation is more common with therapeutic doses of promethazine. The precise mechanism of the CNS effects of the drug is not known.
Promethazine also has antihistaminic, antiemetic, antimotion sickness, anticholinergic, and local anesthetic effects. Although it has been reported that the drug has slight antitussive activity, this may result from its anticholinergic and CNS depressant effects. In therapeutic doses, promethazine appears to have no substantial effect on the cardiovascular system. Although rapid IV administration of promethazine may produce a transient fall in blood pressure, blood pressure usually is maintained or slightly elevated when the drug is given slowly.
Pharmacokinetics
Absorption
Promethazine is well absorbed from the GI tract and from parenteral sites. Plasma concentrations of promethazine required for sedative effects are unknown. The onset of sedative effects occurs within 20 minutes following oral, rectal, or IM administration, and within 3-5 minutes following IV administration. The duration of sedative effects varies but may range from 2-8 hours depending on the dose and route of administration.
Distribution
Promethazine is widely distributed in body tissues. Compared with other organs, lower concentrations of the drug are found in the brain, but this concentration is higher than the plasma concentration. Promethazine has been reported to be 93% protein bound when determined by gas chromatography112 and as 76-80% bound when determined by high-performance liquid chromatography.111 Promethazine readily crosses the placenta.101,103 It is not known whether the drug is distributed into milk.
Elimination
Promethazine is metabolized in the liver. The drug is excreted slowly in urine (mainly) and feces principally as inactive promethazine sulfoxide and glucuronides.
Chemistry and Stability
Chemistry
Promethazine hydrochloride is an ethylamino derivative of phenothiazine and occurs as a racemic mixture. The drug occurs as a white to faint yellow, practically odorless, crystalline powder that slowly oxidizes and turns blue on prolonged exposure to air. Promethazine hydrochloride is very soluble in water and in hot dehydrated alcohol. Commercially available promethazine hydrochloride injection has a pH of 4-5.5. The pKa of the drug is 9.1.
Stability
Promethazine hydrochloride preparations should be protected from light. Promethazine hydrochloride oral solution and tablets should be stored in tight, light-resistant containers at 15-30 and 20-25°C, respectively,100,113 while the rectal suppositories should be stored in well-closed containers at 2-8°C.100 Freezing of the oral solution should be avoided. Following the date of manufacture, commercially available promethazine preparations have expiration dates of 2-5 years depending on the dosage form and manufacturer.
Promethazine hydrochloride injection should be stored in tight, light-resistant containers at 20-25°C, but may be exposed to temperatures ranging from 15-30°C.102 The injection should be discarded if the solution is discolored or contains a precipitate. Promethazine hydrochloride injection has been reported to be chemically incompatible with several drugs, especially those with an alkaline pH. However, the compatibility depends on several factors (e.g., concentration of the drugs, specific diluents used, resulting pH, temperature). Specialized references should be consulted for specific compatibility information.
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