AHFS Class:

• Allylamines 8:14.04

Generic Name(s):

• Terbinafine Hydrochloride

Terbinafine hydrochloride is a synthetic allylamine antifungal agent.1,2,3,10,11,25

Onychomycosis

Oral terbinafine is used for the treatment of dermatophyte infections of the toenail or fingernail (onychomycosis, tinea unguium) caused by susceptible fungi.1,27,28,29,30,31,32,33,34,35,65

Efficacy of terbinafine has been established in uncontrolled and placebo- or comparative drug-controlled studies in patients with toenail1,3,27,28,29,30,31,32,33 or fingernail1,3,31,33,34,35,36,37 onychomycosis. In these studies, patients were assessed for mycologic cure (negative observation of fungus in lesion scrapings prepared with potassium hydroxide, and negative culture of lesion scrapings), effective treatment (mycologic cure and either no nail involvement or more than 5 mm of unaffected new nail growth), or mycologic and clinical (no nail involvement) cure.1,3,27,28,29,30,31,32,33,34,35 Terbinafine has been shown to be active against most strains of Trichophyton rubrum and T. mentagrophytes both in vitro and in clinical infections of the nail.1,27,28,29,30,31,32,33,34,35 Although terbinafine is active in vitro against most strains of Epidermophyton floccosum , Candida albicans , and Scopulariopsis brevicaulis , efficacy of the drug in the treatment of onychomycosis caused by these organisms remains to be established in controlled clinical studies.1

In the toenail studies, 12 weeks of oral therapy with terbinafine 250 mg daily was more effective than placebo29 or itraconazole 200 mg daily,27,28,46 and 16 weeks of oral terbinafine therapy at this dosage was more effective than up to 52 weeks of oral griseofulvin 500 mg daily.30 In these studies, 70-88% of patients experienced mycologic cure,1,27,28,30,46 59% experienced effective treatment,1 and 38-57% experienced mycologic and clinical cure1,27,30 when evaluated 36-48 weeks after completion of terbinafine treatment;1,27,28,46 the clinical relapse rate was about 15% in those evaluated at least 6 months after experiencing clinical cure and at least 1 year after completion of terbinafine treatment.1 In a study comparing 4 months of continuous (250 mg daily) or intermittent (500 mg daily for 1 week each month) oral terbinafine or intermittent (400 mg daily for 1 week each month) oral itraconazole, a trend favoring continuous terbinafine therapy was observed, but statistically significant differences in cure rates among the regimens were not observed.31 In a treatment duration-ranging study comparing 6-, 12-, and 24-weeks of terbinafine therapy in patients with toenail infections, mycologic cure rates were substantially greater for the 12- or 24-week regimens compared with the 6-week regimen, but the 24-week regimen was not substantially more effective than the 12-week regimen.33 However, some patients who do not respond to an initial 12-week course of terbinafine therapy may respond to a second course with the drug.29

In the fingernail studies, 75% of patients experienced effective treatment,1 and 59-90% of patients experienced mycologic and clinical cure1,27,33 when evaluated 18-42 weeks after completion of treatment with oral terbinafine 250 mg daily for 6 weeks.1,27 Extending the course of terbinafine therapy to 12 weeks in patients with fingernail infections does not appear to improve response substantially.33,35 In a study in patients with fingernail onychomycosis who received oral terbinafine 250 mg daily for 2 or 4 weeks, 65% exhibited mycologic and clinical cure 6 months after completion of therapy; the cure rate in those who received only 2 weeks of therapy was 45%.27,34

Terbinafine may be particularly useful in patients who cannot tolerate azole antifungals (e.g., itraconazole) or when there are concerns regarding possible drug interactions between azole antifungals and other drugs the patient is receiving.1,3,26,27,28,38,39,40 However, liver failure (sometimes leading to death or liver transplant) has occurred rarely in patients with or without preexisting liver disease who were receiving oral terbinafine for the treatment of onychomycosis.1,60,71,72 (See Hepatotoxicity under Warnings/Precautions: Warnings, in Cautions.) The choice of antifungal therapy for the treatment of onychomycosis should be individualized27 taking into consideration the prolonged (several months) nature and cost of therapy, and the possibility of relapse.27,48

Tinea Capitis

Oral terbinafine is used for the treatment of tinea capitis (scalp ringworm) caused by susceptible dermatophytes (e.g., Trichophyton , Microsporum ).52,53,54,55,56,57,60,61,62,63,65,68,75,77,78,78,80,81,82

Tinea capitis requires treatment with an oral antifungal.54,55,61,62,65,68,75,77,78 Topical therapies (e.g., shampoos containing selenium sulfide, povidone iodine, or ketoconazole; topical antifungals) are sometimes used as adjuncts to oral antifungal treatment and may reduce fungal shedding and risk of transmission or reinfection.54,55,61,65,68,77,78

Oral griseofulvin generally has been considered the antifungal of choice for the treatment of tinea capitis;55,61,62,63,65,68,75,77,78 alternatives include oral fluconazole, itraconazole, or terbinafine, especially when tinea capitis does not respond to griseofulvin or when there are compliance problems with the griseofulvin regimen.55,61,62,63,65,68,75,77

Oral terbinafine appears to be as effective as oral griseofulvin for the treatment of tinea capitis caused by Trichophyton , and requires a shorter duration of treatment which may increase compliance.55,61,62,63,65 However, there is some evidence that griseofulvin may be more effective than terbinafine when tinea capitis is caused by M. canis .55,56,57,61,62,63

Tinea Corporis or Tinea Cruris

Oral terbinafine has been used for the treatment of tinea corporis† (body ringworm)53,55,56,65,75 or tinea cruris† (jock itch).65,75

Topical antifungals usually are effective for the treatment of uncomplicated tinea corporis.55,65,73,74,75,76 An oral antifungal (griseofulvin, fluconazole, itraconazole, terbinafine) may be necessary if tinea corporis is extensive, dermatophyte folliculitis is present, the infection does not respond to topical therapy, or the patient is immunocompromised because of coexisting disease or concomitant therapy.55,65,73,74,75,76

For information on topical uses of terbinafine, see Terbinafine 84:04.08.

Administration

Terbinafine hydrochloride is administered orally.1,60

Terbinafine hydrochloride oral granules should be taken with food.60 The contents of the single-dose packet should be sprinkled on a spoonful of pudding or other soft, nonacidic food (e.g., mashed potatoes);60 applesauce or fruit-based food should not be used.60 The entire spoonful should be swallowed (without chewing).60 If the indicated dosage requires 2 packets for each dose, the contents of both packets may be sprinkled on a single spoonful of nonacidic food or the contents of the packets may be sprinkled on 2 spoonfuls of nonacidic food.60

Dosage

Dosage of terbinafine hydrochloride is expressed in terms of terbinafine.1,60

Terbinafine hydrochloride tablets are used in adults;1 terbinafine hydrochloride oral granules are used in adults or children 4 years of age or older.60

Onychomycosis

The usual adult dosage of oral terbinafine for the treatment of onychomycosis (tinea unguium) of the fingernail is 250 mg daily given for 6 weeks.1,3,10,27 Fingernail infections usually are reevaluated 18 weeks or longer after completion of therapy.1,10,27,35

The usual adult dosage of oral terbinafine for the treatment of onychomycosis of the toenail is 250 mg daily given for 12 weeks.1,10,27,28,29,33,46 Toenail infections usually are reevaluated 6-9 months after completion of therapy.1,10,28,29

Toenail infections generally require more prolonged antifungal therapy than fingernail infections.1,3,27,28,29,30,31,32,33,34,35 Although there is no evidence that continuing terbinafine therapy longer than recommended increases efficacy for the treatment of onychomycosis,33 some patients may benefit from extended and/or repeated courses of terbinafine therapy.3,29,33,50

Tinea Capitis

The usual dosage of terbinafine oral granules for the treatment of tinea capitis in adults or children 4 years of age or older is 125-250 mg once daily for 6 weeks.60 Those weighing less than 25 kg should receive a dosage of 125 mg once daily, those weighing 25-35 kg should receive 187.5 mg once daily, and those weighing more than 35 kg should receive 250 mg once daily.60

There is some evidence that a longer duration of treatment (e.g., 6-8 weeks) or higher dosage may be necessary when tinea capitis is caused by Microsporum canis .57,61,65,68,77

Tinea Corporis or Tinea Cruris

Although safety and efficacy have not been established, oral terbinafine has been given in a dosage of 250 mg daily for 2-4 weeks for the treatment of tinea corporis† or tinea cruris†.65,75

Special Populations

Because clearance of terbinafine may be decreased substantially in patients with renal impairment (i.e., creatinine clearance of 50 mL/minute or less) or in those with preexisting liver disease (e.g., cirrhosis),1,60 the manufacturer states that the drug is not recommended in such patients.1,60 (See Cautions: Specific Populations.)

Contraindications

Hypersensitivity to terbinafine1,60 or any ingredient in the formulation.1

Warnings/Precautions

Warnings

Hepatotoxicity

Hepatotoxicity, including abnormal liver function tests and severe cholestatic hepatitis, has been reported in some patients receiving oral terbinafine.1,60,69,70,71,72

Liver failure, sometimes leading to death or liver transplant, has occurred rarely in patients with or without preexisting liver disease receiving oral terbinafine for treatment of onychomycosis.1,60,71,72 Most patients had serious underlying systemic conditions;1,60 severity and outcome of hepatotoxicity may be worse in patients with active or chronic liver disease.1,60

Not recommended in patients with chronic or active liver disease.1,60

Assess hepatic function (serum AST and ALT) prior to initiation of oral terbinafine.1

Discontinue terbinafine if there is biochemical or clinical evidence of liver injury,1,60 including increased ALT or AST concentrations, persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain or jaundice, dark urine, or pale stools.1,60

Hematologic Effects

Transient decrease in absolute lymphocyte count (ALC) reported; clinical importance unknown.1,60 Severe neutropenia reported rarely; resolved with or without supportive therapy when terbinafine was discontinued.1,60

Thrombocytopenia,1,60 agranulocytosis,1,60 pancytopenia,60 and anemia60 reported during postmarketing surveillance; causal relationship not established.60

In patients with suspected immunodeficiency, consider monitoring complete blood cell counts (CBCs) if oral terbinafine is continued for longer than 6 weeks.1,60

If clinical signs and symptoms suggest secondary infection, perform CBC.1,60 If neutrophil count is 1000/mm³ or lower, discontinue terbinafine and initiate supportive therapy.1,60

Dermatologic Effects

Serious skin reactions (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis) reported rarely.1,60

Psoriasiform eruptions or exacerbation of psoriasis and acute, generalized exanthematous pustulosis reported.1,60,47

If progressive rash occurs, discontinue terbinafine.1,60

Lupus Erythematosus

Precipitation and exacerbation of cutaneous and systemic lupus erythematosus reported.1,60

If patient develops clinical signs and symptoms suggestive of lupus erythematosus, discontinue terbinafine.1,60

Sensitivity Reactions

Hypersensitivity Reactions

Angioedema and allergic reactions, including anaphylaxis, reported rarely.1,60

General Precautions

Ocular Effects

Visual disturbances, including changes in ocular lens and retina, reported following use of terbinafine tablets for treatment of onychomycosis in adults;1,60 clinical importance unknown.1,60

Although no ophthalmologic safety signal was identified in clinical trials using terbinafine oral granules, there were some reports of changes in visual acuity and some reports of color confusion in yellow-blue color vision assessments.60

GI Effects

Taste disturbances (including taste loss) may occur.1,60 This usually resolves within several weeks after terbinafine is discontinued, but prolonged (more than 1 year) taste disturbance has been reported.1,60 May be severe enough to result in decreased food intake leading to substantial and unwanted weight loss.1,60

Selection and Use of Antifungals for Onychomycosis

Prior to administration of oral terbinafine for treatment of onychomycosis, appropriate nail specimens for microbiologic studies (e.g., potassium hydroxide [KOH] preparation, fungal culture, or nail biopsy) should be obtained to confirm the diagnosis.1

When selecting an antifungal for treatment of onychomycosis, consider reported adverse effects and risk of serious effects, need for prolonged therapy, cost, and risk of relapse.27,48

Toenail infections generally require more prolonged antifungal therapy than fingernail infections.1,3,27,28,29,30,31,32,33,34,35

The optimal clinical effect of terbinafine in treatment of onychomycosis is not seen until several months after mycologic cure and completion of treatment, and is related to the period required for outgrowth of healthy nail.1,28,34,35

Possible Prescribing and Dispensing Errors

Because of the similarity in spelling between Lamisil^® (the trade name for terbinafine hydrochloride) and Lamictal^® (the trade name for lamotrigine, an anticonvulsant agent), several dispensing errors have been reported to the manufacturer of Lamictal^® (GlaxoSmithKline).58,59 These medication errors may be associated with serious adverse events either due to lack of appropriate therapy for seizures (e.g., in patients not receiving the prescribed anticonvulsant, lamotrigine, which may lead to status epilepticus) or, alternatively, to the risk of developing adverse effects (e.g., serious rash) associated with the use of lamotrigine in patients for whom the drug was not prescribed and consequently was not properly titrated.58,59

The manufacturer of Lamictal^® cautions that extra care should be exercised in ensuring the accuracy of both oral and written prescriptions for Lamictal^® and Lamisil^®.58,59 The manufacturer also recommends that when appropriate, clinicians might consider including the intended use of the particular drug on the prescription in addition to alerting patients to carefully check the drug they receive and promptly bring any question or concern to the attention of the dispensing pharmacist.58 In addition, it is recommended that pharmacists assess the measures of avoiding dispensing errors and implement them as appropriate (e.g., placing drugs with similar names apart from one another in product storage areas, patient counseling).59

Specific Populations

Pregnancy

Category B.1,60 (See Users Guide.)

The manufacturer recommends that use of oral terbinafine be postponed until after pregnancy is completed.1,60

Lactation

Distributed into milk.1,60 Use not recommended.1,60

Pediatric Use

Safety and efficacy of terbinafine tablets not established in children1 younger than 18 years of age.51

Safety and efficacy of terbinafine oral granules not established in children younger than 4 years of age.60

Geriatric Use

Terbinafine oral granules have not been studied in geriatric patients.60

Hepatic Impairment

Clearance of terbinafine may be decreased substantially (about 50%) in adults with hepatic cirrhosis.1,3,60

Use of terbinafine not recommended in patients with chronic or active liver disease.1,27,60 (See Hepatotoxicity under Warnings/Precautions: Warnings, in Cautions.)

Renal Impairment

Clearance of terbinafine may be decreased substantially (about 50%) in adults with renal impairment (creatinine clearance 50 mL/minute or lower).1,3,60

Use of terbinafine has not been adequately studied in patients with creatinine clearance of 50 mL/minute or lower, and1,27,60 use in such patients is not recommended.1

Common Adverse Effects

The most frequent adverse effects of oral terbinafine are GI effects (diarrhea, dyspepsia, nausea, vomiting, abdominal pain, taste disturbances),1,60,63 headache,60,63 fever,60,63 upper respiratory tract infection or symptoms (cough, nasopharyngitis, nasal congestion, pharyngolaryngeal pain, influenza),60,63 liver test abnormalities,1 and dermatologic effects (rash, urticaria, pruritus).1,60

Drugs Metabolized by Hepatic Microsomal Enzymes

Terbinafine inhibits the cytochrome P-450 (CYP) isoenzyme CYP2D6.1,60 There is a possibility of pharmacokinetic interactions with drugs that are substrates for CYP2D6 (e.g., tricyclic antidepressants, β-blockers, selective serotonin reuptake inhibitors [SSRIs], monoamine oxidase [MAO] inhibitors).1,60 If terbinafine is used concomitantly with drugs that are metabolized by CYP2D6, patients should be monitored carefully and dosage of such drugs may need to be reduced.1,60

Antiarrhythmic Agents

Concomitant use of terbinafine and antiarrhythmic agents that are metabolized by CYP2D6 (e.g., flecainide, propafenone) may result in increased concentrations of the antiarrhythmic agent.1,60 If terbinafine is used concomitantly with such antiarrhythmic agents, the patient should be monitored carefully and a reduced dosage of the antiarrhythmic agent may be required.1,60

Because amiodarone inhibits CYP2C9 and CYP3A isoenzymes and because terbinafine is metabolized by these enzymes, concomitant use of the drugs may result in substantially increased peak serum concentrations and area under the concentration-time curve (AUC) of terbinafine.60

Antidepressants

Concomitant use of terbinafine and antidepressants that are metabolized by CYP2D6 (e.g., tricyclics, SSRIs, MAO inhibitors) may result in increased concentrations of the antidepressant.1,60

When oral terbinafine was used concomitantly with oral desipramine, a twofold increase in peak plasma concentrations and a fivefold increase in the AUC of desipramine occurred.1,60 These effects on the pharmacokinetics of desipramine persisted for at least 4 weeks after terbinafine was discontinued.1,60

If terbinafine is used concomitantly with desipramine or other antidepressants metabolized by CYP2D6, the patient should be monitored carefully and a reduced dosage of the antidepressant may be required.1,60

Antifungal Agents

Concomitant use of oral terbinafine and oral fluconazole results in substantially increased peak serum concentrations and AUC of terbinafine, but does not have a clinically important effect on fluconazole pharmacokinetics.60 Fluconazole inhibits CYP2C9 and CYP3A isoenzymes; therefore, other antifungals that inhibit these CYP isoenzymes (e.g., ketoconazole) also may result in substantial increases in systemic exposure to terbinafine.60

Benzodiazepines

Concomitant use of oral terbinafine and midazolam or triazolam does not have a clinically important effect on the pharmacokinetics of the benzodiazepine.39,40

Caffeine

Terbinafine decreases clearance of caffeine by 19%.1,60

Cimetidine

Concomitant use of oral terbinafine and cimetidine results in a 33% decrease in terbinafine clearance.1,60

Cyclosporine

Concomitant use of oral terbinafine and cyclosporine results in a 15% increase in cyclosporine clearance;1,60 terbinafine clearance is not affected.1,60

Dextromethorphan

Concomitant use of oral terbinafine and dextromethorphan in individuals characterized as extensive metabolizers of dextromethorphan results in a 16- to 97-fold increase in the dextromethorphan/dextromethorphan metabolite ratio in urine.60

Digoxin

In a study in healthy individuals, concomitant use of oral terbinafine and digoxin did not affect digoxin clearance.1,60

Rifampin

Concomitant use of oral terbinafine and rifampin results in a 100% increase in terbinafine clearance.1,60

Sulfamethoxazole

Terbinafine does not have a clinically important effect on the pharmacokinetics of sulfamethoxazole.60

Theophylline

Terbinafine does not have a clinically important effect on the pharmacokinetics of theophylline.60

Trimethoprim

Terbinafine does not have a clinically important effect on the pharmacokinetics of trimethoprim.60

Warfarin

Although a causal relationship has not been established, concomitant use of oral terbinafine and warfarin has resulted in increased or decreased prothrombin times.1,60

Zidovudine

Terbinafine does not have a clinically important effect on the pharmacokinetics of zidovudine.60

Pharmacokinetics

Absorption

Bioavailability

Following oral administration of granules containing terbinafine hydrochloride in children 4-8 years of age, peak serum concentrations and areas under the concentration-time curve (AUCs) exhibit considerable interindividual variability (36-64%).60

Following oral administration of tablets containing terbinafine hydrochloride, peak plasma concentrations are attained within 1.4-2 hours.1,64 Bioavailability is 40% as the result of first-pass metabolism.1 Following multiple oral doses, steady-state peak concentration and AUC are 25% higher than those reported following a single oral dose.1 Considerable interindividual variability in systemic exposure has been reported in adults or children.64

Food

The effect of food on bioavailability of terbinafine granules has not been studied.60 In clinical trials evaluating use of the granules for treatment of tinea capitis, the granules were given with food.60

Food increases the AUC of terbinafine by less than 20%;1 this is not considered clinically important.3,50,51

Distribution

Extent

Terbinafine is highly lipophilic and keratophilic and distributes in high concentrations into stratum corneum, sebum, hair, and nail matrix, bed, and plate; the drug persists in these tissues for several weeks to months after discontinuance.3,10,27,34,41,42,43

Terbinafine is distributed into milk following oral administration.1,60

Plasma Protein Binding

Terbinafine is more than 99% bound to plasma proteins.1,60

Elimination

Metabolism

Terbinafine is rapidly and extensively metabolized by at least 7 different cytochrome P-450 (CYP) isoenzymes, including 2C9, 1A2, 3A4, 2C8, and 2C19.60

No terbinafine metabolites with antifungal activity have been identified to date.1,60

Elimination Route

Approximately 70% of an oral dose of terbinafine is eliminated in urine.1,60

Half-life

A terbinafine terminal half-life of 200-400 hours has been reported and may represent slow elimination of the drug from tissues (e.g., skin, adipose).1

Following multiple oral doses of terbinafine granules in children 4-8 years of age, the mean effective half-life obtained from the observed accumulation was 26.7 or 30.5 hours for 125- or 187.5-mg doses, respectively.60

Special Populations

Clearance of terbinafine is decreased by about 50% in adults with renal impairment (creatinine clearance 50 mL/minute or less) or with hepatic cirrhosis.1,3,60

Description

Terbinafine hydrochloride is a synthetic allylamine antifungal agent.1,2,3,10,25,27,28,33 Terbinafine is structurally and pharmacologically related to naftifine.2,3,7,10,11,12,13,25

Terbinafine is commercially available for oral administration as tablets or film-coated granules containing terbinafine hydrochloride.1,60 The tablets should be stored at less than 25°C in a tight container and should be protected from light.1 The oral granules should be stored at 25°C, but may be exposed to temperatures ranging from 15-30°C.60

Mechanism of Action

The exact mechanism of action of terbinafine's antifungal activity has not been fully determined.1,3,14,17,19,22,24,25 The drug interferes with sterol biosynthesis by inhibiting the enzyme squalene monooxygenase (squalene 2,3-epoxidase).1,2,3,17,18,19,20,22,24,25,27 The resulting accumulation of squalene (the usual substrate of the enzyme) in the cells, and decreased amounts of sterols, especially ergosterol,1,3,14,16,17,19,22,25,27,50 are both thought to contribute to the antifungal action of terbinafine.2,3,10,25,27

Results from in vitro studies indicate that terbinafine may be fungicidal or fungistatic, depending on the concentration of the drug and the species tested,1,2,3,25 but the clinical importance of these in vitro findings are unknown.1,3,27 The drug appears to be fungicidal against dermatophytes (e.g., Trichophyton , Epidermophyton . Microsporum ), but may be fungicidal or fungistatic against yeasts (e.g., Candida parapsilosis or C. albicans , respectively).2,3,25 The fungicidal effect of terbinafine may principally be related to the toxic accumulation of squalene,3,10,25 probably in combination with ergosterol depletion.25 Cellular death in several different fungi treated in vitro with terbinafine was always associated with a large increase in intracellular squalene concentrations, but not always with marked decreases in ergosterol,25 and a fungicidal effect is achieved in vitro in some fungi at terbinafine concentrations that do not completely prevent ergosterol biosynthesis.3,10,25 Following doses 100 times greater than those that are fungicidal to dermatophytes, the drug achieves only 80% reductions in viable cell counts of some yeasts (e.g., C. albicans ), and the fungistatic effect of terbinafine against C. albicans is thought to result from inhibition in ergosterol synthesis with resultant depletion of ergosterol.3,10 There may be a greater susceptibility of the hyphal or filamentous form than that of the yeast form of C. albicans to the disruptive effects of terbinafine and other (e.g., azole) antifungal agents on sterol biosynthesis,25 and the ability of terbinafine to suppress the invasive hyphal form of C. albicans may play an important role in its therapeutic efficacy against this organism.25

Squalene monooxygenase, similar to that contained in fungi, is involved in mammalian cholesterol synthesis; however, studies using rat liver indicate that the mammalian enzyme is 3 or 4 orders of magnitude (i.e., between 1000-10,000 times) less sensitive than the fungal enzyme to the effects of terbinafine.2,3,17,19,25 The manufacturer states that inhibition of mammalian squalene monooxygenase would require terbinafine concentrations that are 4000-fold higher than those required for fungicidal activity in vitro.1

Although azole antifungal agents, including imidazole derivatives (e.g., clotrimazole, econazole, ketoconazole, miconazole) and triazole derivatives (e.g., fluconazole, itraconazole) also appear to exert their antifungal activity by interfering with sterol biosynthesis, the mechanism of action of these antifungal agents differs from that of terbinafine and other allylamine derivatives.17,21,24 The allylamine derivatives appear to affect sterol biosynthesis at an earlier stage than do azole antifungal agents and do not appear to affect C-14 demethylation of sterol intermediates (e.g., lanosterol).17,22,24 Also, the squalene epoxidase enzyme target of terbinafine and other allylamine derivatives is not a cytochrome P-450 type enzyme,17,21,24,25 and terbinafine and other allylamine derivatives have less effect on the microsomal cytochrome P-450 systems in the liver, adrenal glands, or testes than imidazole derivatives.3,17,21,24,25,38,39,40,49,50

Spectrum

Terbinafine has an antifungal spectrum of activity similar to that of naftifine3,4,10,13 and is active in vitro against many fungi, including dermatophytes ( Trichophyton , Microsporum , Epidermophyton ) and filamentous (e.g. Aspergillus ), dimorphic (e.g., Blastomyces ), and dematiaceous fungi and yeasts.3,25,27,3,25,27 Terbinafine is more active than azole antifungal agents, including imidazole derivatives (e.g., ketoconazole) or triazole derivatives (e.g., fluconazole, itraconazole) against dermatophytes,3,6,8,13,44 but is less active than these drugs against Candida .3,9,10,44

Terbinafine usually is fungicidal in action against susceptible dermatophytes.3,4,5,10,13 The drug is active against most strains of T. rubrum and T. mentagrophytes in vitro and in vivo in clinical infections of the nail.1,27,28,29,30,31,32,33,34,35 Terbinafine also usually is active in vitro against T. tonsurans ,66 T. violaceum ,66 E. floccosum ,3,6,8,13,44 and Microsporum ,3,6,8,13,44 including M. audouinii 66 and M. canis .66 The MIC₉₀ of terbinafine reported for M. canis has been higher than that reported for Trichophyton or M. audouinii .66

Terbinafine is active in vitro against Aspergillus , Blastomyces , Histoplasma , and certain other fungi and yeasts,3,4,5,10,13 including C. parapsilosis , but is only fungistatic against C. albicans ; like naftifine, terbinafine may be fungicidal against C. albicans at high concentrations.3,10,15,18,22,23,25

Terbinafine is active in vitro against most strains of C. albicans and Scopulariopsis brevicaulis .1 However, the efficacy of terbinafine in treating infections caused by these organisms has not been established in clinical studies, and it remains to be established whether in vitro susceptibility tests accurately reflect in vivo (clinical) activity for various fungi.1,3,12,27

Advice to Patients

Importance of using terbinafine for the full, prescribed treatment period.60

If using oral granules, importance of taking once daily with food.60 Advise patients to sprinkle contents of packet containing granules on a spoonful of pudding or other soft, nonacidic food (e.g., mashed potatoes) and to swallow the food and granules without chewing.60 Importance of not to taking with applesauce or fruit-based foods.60

Advise patients of the risk of hepatotoxicity and importance of discontinuing the drug and contacting a clinician if they experience persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain or jaundice, dark urine, or pale stools.1,60

Advise patients to discontinue terbinafine and contact a clinician if a progressive rash occurs.1,60

Advise patients to contact a clinician if they experience prolonged taste disturbances severe enough to result in decreased food intake since this may lead to substantial and unwanted weight loss.60

When used to treat onychomycosis, advise patients that optimal clinical effect of terbinafine is delayed for several months after mycologic cure and completion of treatment because of the time required for outgrowth of healthy nail.1,28,34,35

Importance of informing clinician of existing or contemplated concomitant therapy, including prescription and OTC drugs, and other concomitant illnesses.1,60

Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.1,60

Importance of advising patients of other important precautionary information.1,60 (See Cautions.)

Additional Information

Overview^® (see Users Guide). For additional information on this drug until a more detailed monograph is developed and published, the manufacturer's labeling should be consulted. It is essential that the manufacturer's labeling be consulted for more detailed information on usual cautions, precautions, contraindications, potential drug interactions, laboratory test interferences, and acute toxicity.

1. Novartis. Lamisil^® (terbinafine hydrochloride) tablets prescribing information. East Hanover, NJ; 2005 Nov.

2. Petranyi G, Ryder NS, Stutz A. Allylamine derivatives: new class of synthetic antifungal agents inhibiting fungal squalene epoxidase. Science . 1984; 224:1239-41. [PubMed 6547247]

3. Balfour JA, Faulds D. Terbinafine: a review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in superficial mycoses. Drugs . 1992; 43: 259-84.

4. Savin RC. Treatment of chronic tinea pedis (athlete's foot type) with topical terbinafine. J Am Acad Dermatol . 1990; 23:786-9. [PubMed 2229524]

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