Terbinafine Drug Information

Terbinafine tablets are indicated for the treatment of onychomycosis of the toenail or fingernail due to dermatophytes (tinea unguium). Prior to initiating treatment, appropriate nail specimens for laboratory testing should be obtained to confirm the diagnosis of onychomycosis. Terbinafine tablets are an allylamine antifungal indicated for the treatment of onychomycosis of the toenail or fingernail due to dermatophytes (tinea unguium).

• Prior to administering, evaluate patients for evidence of chronic or active liver disease.
• Fingernail onychomycosis: One tablet, once daily for 6 weeks.
• Toenail onychomycosis: One tablet, once daily for 12 weeks. 2.1 Assessment Prior to Initiation Before administering terbinafine tablets, evaluate patients for evidence of chronic or active liver disease [see Contraindications (4) and ]. 2.2 Dosage Fingernail onychomycosis: One 250 mg tablet once daily for 6 weeks. Toenail onychomycosis: One 250 mg tablet once daily for 12 weeks. The optimal clinical effect is seen some months after mycological cure and cessation of treatment. This is related to the period required for outgrowth of healthy nail.

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The most frequently reported adverse events observed in the 3 U.S./Canadian placebo-controlled trials are listed in the Table 1. The adverse events reported encompass gastrointestinal symptoms (including diarrhea, dyspepsia, and abdominal pain), liver test abnormalities, rashes, urticaria, pruritus, and taste disturbances. Changes in the ocular lens and retina have been reported following the use of terbinafine tablets in controlled trials.

The clinical significance of these changes is unknown. In general, the adverse events were mild, transient, and did not lead to discontinuation from study participation. Table 1. Most frequently reported adverse events observed in the 3 U.S./Canadian placebo-controlled trials Adverse Event Discontinuation Terbinafine Tablets (%) n=465 Placebo (%) n=137 Terbinafine Tablets (%) n=465 Placebo (%) n=137 * Liver enzyme abnormalities greater than or equal to 2 times the upper limit of normal range.

Headache 12.9 9.5 0.2 0 Gastrointestinal Symptoms: Diarrhea Dyspepsia Abdominal Pain Nausea Flatulence 5.6 4.3 2.4 2.6 2.2 2.9 2.9 1.5 2.9 2.2 0.6 0.4 0.4 0.2 0 0 0 0 0 0 Dermatological Symptoms: Rash Pruritus Urticaria 5.6 2.8 1.1 2.2 1.5 0 0.9 0.2 0 0.7 0 0 Liver Enzyme Abnormalities* 3.3 1.4 0.2 0 Taste Disturbance 2.8 0.7 0.2 0 Visual Disturbance 1.1 1.5 0.9 0

Postmarketing Experience

The following adverse events have been identified during post-approval use of terbinafine tablets. Because these events are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Blood and lymphatic system disorders: Pancytopenia, agranulocytosis, severe neutropenia, thrombocytopenia, anemia, thrombotic microangiopathy (TMA), including thrombotic thrombocytopenic purpura and hemolytic uremic syndrome Immune system disorders: Serious hypersensitivity reactions e.g., angioedema and allergic reactions (including anaphylaxis), precipitation and exacerbation of cutaneous and systemic lupus erythematosus, serum sickness-like reaction Psychiatric disorders: Anxiety and depressive symptoms independent of taste disturbance have been reported with use of terbinafine tablets.

In some cases, depressive symptoms have been reported to subside with discontinuance of therapy and to recur with reinstitution of therapy. Nervous system disorders: Cases of taste disturbance, including taste loss, have been reported with the use of terbinafine tablets. It can be severe enough to result in decreased food intake, weight loss, anxiety, and depressive symptoms.

Cases of smell disturbance, including smell loss, have been reported with the use of terbinafine tablets. Cases of paresthesia and hypoesthesia have been reported with the use of terbinafine tablets. Eye disorders: Visual field defects, reduced visual acuity Ear and labyrinth disorders: Hearing impairment, vertigo, tinnitus Vascular disorders: Vasculitis Gastrointestinal disorders: Pancreatitis, vomiting Hepatobiliary disorders: Cases of liver failure some leading to liver transplant or death, idiosyncratic and symptomatic hepatic injury.

Cases of hepatitis, cholestasis, and increased hepatic enzymes have been seen with the use of terbinafine tablets. Skin and subcutaneous tissue disorders: Serious skin reactions , acute generalized exanthematous pustulosis, psoriasiform eruptions or exacerbation of psoriasis, photosensitivity reactions, hair loss Musculoskeletal and connective tissue disorders: Rhabdomyolysis, arthralgia, myalgia General disorders and administration site conditions: Malaise, fatigue, influenza-like illness, pyrexia Investigations: Altered prothrombin time (prolongation and reduction) in patients concomitantly treated with warfarin and increased blood creatine phosphokinase have been reported

Drug-Drug Interactions

In vivo studies have shown that terbinafine is an inhibitor of the CYP450 2D6 isozyme. Drugs predominantly metabolized by the CYP450 2D6 isozyme include the following drug classes: tricyclic antidepressants, selective serotonin reuptake inhibitors, beta-blockers, antiarrhythmics class 1C (e.g., flecainide and propafenone) and monoamine oxidase inhibitors Type B. Coadministration of terbinafine tablets should be done with careful monitoring and may require a reduction in dose of the 2D6-metabolized drug. In a study to assess the effects of terbinafine on desipramine in healthy volunteers characterized as normal metabolizers, the administration of terbinafine resulted in a 2-fold increase in C max and a 5-fold increase in area under the curve (AUC). In this study, these effects were shown to persist at the last observation at 4 weeks after discontinuation of terbinafine tablets.

In studies in healthy subjects characterized as extensive metabolizers of dextromethorphan (antitussive drug and CYP2D6 probe substrate), terbinafine increases the dextromethorphan/dextrorphan metabolite ratio in urine by 16- to 97-fold on average. Thus, terbinafine may convert extensive CYP2D6 metabolizers to poor metabolizer status. In vitro studies with human liver microsomes showed that terbinafine does not inhibit the metabolism of tolbutamide, ethinylestradiol, ethoxycoumarin, cyclosporine, cisapride and fluvastatin.

In vivo drug-drug interaction studies conducted in healthy volunteer subjects showed that terbinafine does not affect the clearance of antipyrine or digoxin. Terbinafine decreases the clearance of caffeine by 19%. Terbinafine increases the clearance of cyclosporine by 15%. The influence of terbinafine on the pharmacokinetics of fluconazole, cotrimoxazole (trimethoprim and sulfamethoxazole), zidovudine or theophylline was not considered to be clinically significant. Coadministration of a single dose of fluconazole (100 mg) with a single dose of terbinafine resulted in a 52% and 69% increase in terbinafine C max and AUC, respectively.

Fluconazole is an inhibitor of CYP2C9 and CYP3A enzymes. Based on this finding, it is likely that other inhibitors of both CYP2C9 and CYP3A4 (e.g., ketoconazole, amiodarone) may also lead to a substantial increase in the systemic exposure (C max and AUC) of terbinafine when concomitantly administered. There have been spontaneous reports of increase or decrease in prothrombin times in patients concomitantly taking oral terbinafine and warfarin, however, a causal relationship between terbinafine tablets and these changes has not been established.

Terbinafine clearance is increased 100% by rifampin, a CYP450 enzyme inducer, and decreased 33% by cimetidine, a CYP450 enzyme inhibitor. Terbinafine clearance is unaffected by cyclosporine. There is no information available from adequate drug-drug interaction studies with the following classes of drugs: oral contraceptives, hormone replacement therapies, hypoglycemics, phenytoins, thiazide diuretics, and calcium channel blockers.

Food Interactions

An evaluation of the effect of food on terbinafine tablets was conducted. An increase of less than 20% of the AUC of terbinafine was observed when terbinafine tablets were administered with food. Terbinafine tablets can be taken with or without food.

Pregnancy Risk Summary Available data from postmarketing cases on the use of terbinafine tablets in pregnant women are insufficient to evaluate a drug-associated risk of major birth defects, miscarriage, or adverse maternal or fetal outcomes. In animal reproduction studies, terbinafine did not cause malformations or any harm to the fetus when administered to pregnant rabbits and rats during the period of organogenesis at oral doses up to 12 and 23 times the maximum recommended human dose (MRHD) of 250 mg/day, respectively (see data). All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. The background risk of major birth defects and miscarriage for the indicated population is unknown; however, in the U.S. general population, the estimated background risk of major birth defects is 2% to 4% and of miscarriage is 15% to 20% of clinically recognized pregnancies.

Data Animal Data In embryo-fetal development studies in rats and rabbits, pregnant animals received orally (by gavage) doses of terbinafine up to 300 mg/kg/day, during the period of organogenesis. There were no maternal or embryo-fetal effects in either species up to the maximum dose tested. The 300 mg/kg/day dose level in rats and rabbits corresponds to 23 and 12 times the MRHD, respectively.

In a rat peri- and postnatal development study, terbinafine doses of up to 300 mg/kg/day (12 times the MRHD based on BSA comparisons) given by oral gavage during late pregnancy and lactation (Day 15 of gestation to day 20 post-partum) had no adverse effects on parturition and lactation.

Pediatric Use The safety and efficacy of terbinafine tablets have not been established in pediatric patients with onychomycosis.

• Terbinafine tablets are contraindicated in patients with:
• Chronic or active liver disease [see ]
• History of allergic reaction to oral terbinafine because of the risk of anaphylaxis [see ]
• Chronic or active liver disease. (4)
• History of allergic reaction to oral terbinafine because of the risk of anaphylaxis. (4)

Clinical experience regarding overdose with oral terbinafine is limited. Doses up to 5 grams (20 times the therapeutic daily dose) have been taken without inducing serious adverse reactions. The symptoms of overdose included nausea, vomiting, abdominal pain, dizziness, rash, frequent urination, and headache.