Terbinafine Hydrochloride

Cases of liver failure, some leading to liver transplant or death, have occurred with the use of terbinafine tablets in individuals with and without pre-existing liver disease.  

In the majority of liver cases reported in association with terbinafine hydrochloride use, the patients had serious underlying systemic conditions. The severity of hepatic events and/or their outcome may be worse in patients with active or chronic liver disease. Treatment with terbinafine tablets should be discontinued if biochemical or clinical evidence of liver injury develops.  

Terbinafine tablets are not recommended for patients with chronic or active liver disease. Before prescribing terbinafine tablets, pre-existing liver disease should be assessed. Hepatotoxicity may occur in patients with and without pre-existing liver disease. Patients prescribed terbinafine tablets should be warned to report immediately to their physician any symptoms of persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain or jaundice, dark urine or pale stools. Patients with these symptoms should discontinue taking oral terbinafine, and the patient’s liver function should be immediately evaluated.

Taste disturbance, including taste loss, has been reported with the use of terbinafine tablets. It can be severe enough to result in decreased food intake, weight loss, and depressive symptoms. Taste disturbance may resolve within several weeks after discontinuation of treatment, but may be prolonged (greater than one year), or may be permanent. If symptoms of a taste disturbance occur, terbinafine tablets should be discontinued.

Smell disturbance, including loss of smell, has been reported with the use of terbinafine tablets. Smell disturbance may resolve after discontinuation of treatment, but may be prolonged (greater than one year), or may be permanent. If symptoms of a smell disturbance occur, terbinafine tablets should be discontinued.

Depressive symptoms have occurred during postmarketing use of terbinafine. Prescribers should be alert to depressive symptoms, and patients should be instructed to report depressive symptoms to their physician.

Transient decreases in absolute lymphocyte counts (ALC) have been observed in controlled clinical trials. In placebo-controlled trials, 8/465 terbinafine hydrochloride-treated patients (1.7%) and 3/137 placebo-treated patients (2.2%) had decreases in ALC to below 1000/mm³ on two or more occasions. In patients with known or suspected immunodeficiency, physicians should consider monitoring complete blood counts if treatment continues for more than six weeks. Cases of severe neutropenia have been reported. These were reversible upon discontinuation of terbinafine hydrochloride, with or without supportive therapy. If clinical signs and symptoms suggestive of secondary infection occur, a complete blood count should be obtained. If the neutrophil count is <1,000 cells/mm³, terbinafine hydrochloride should be discontinued and supportive management started.

There have been postmarketing reports of serious skin reactions (e.g., Stevens-Johnson Syndrome and toxic epidermal necrolysis). If progressive skin rash occurs, treatment with terbinafine tablets should be discontinued.

During post-marketing experience, precipitation and exacerbation of cutaneous and systemic lupus erythematosus have been reported in patients taking terbinafine tablets. Terbinafine tablets should be discontinued in patients with clinical signs and symptoms suggestive of lupus erythematosus.

Measurement of serum transaminases (ALT and AST) is advised for all patients before taking terbinafine tablets.

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 three US/Canadian placebo-controlled trials are listed in the table below. 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.   

* Liver enzyme abnormalities ≥ 2x the upper limit of normal range.

The following adverse events have been identified during post-approval use of terbinafine hydrochloride. 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.  

Adverse events, based on worldwide experience with terbinafine tablets use, include: idiosyncratic and symptomatic hepatic injury and more rarely, cases of liver failure, some leading to death or liver transplant, serious skin reactions (e.g., Stevens-Johnson Syndrome and toxic epidermal necrolysis), severe neutropenia, thrombocytopenia, agranulocytosis, pancytopenia, anemia, angioedema, and allergic reactions (including anaphylaxis) [see Warnings and Precautions (5.1, 5.5 , and 5.6)].  

Psoriasiform eruptions or exacerbation of psoriasis, acute generalized exanthematous pustulosis and precipitation and exacerbation of cutaneous and systemic lupus erythematosus have been reported in patients taking terbinafine hydrochloride [see Warnings and Precautions (5.7)].  

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, and depressive symptoms [see Warnings and Precautions (5.2)]. 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 [see Warnings and Precautions (5.4)]. Cases of smell disturbance, including smell loss, have been reported with the use of terbinafine tablets [see Warnings and Precautions (5.3)].  

Other adverse reactions which have been reported include malaise, fatigue, vomiting, arthralgia, myalgia, rhabdomyolysis, reduced visual acuity, visual field defect, hair loss, serum sickness-like reaction, vasculitis, pancreatitis, influenza-like illness, pyrexia, increased blood creatine phosphokinase, photosensitivity reactions, tinnitus, hearing impairment and vertigo.

Altered prothrombin time (prolongation and reduction) in patients concomitantly treated with warfarin has been reported.

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 hydrochloride 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 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.

Co-administration of a single dose of fluconazole (100mg) 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.

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

Pregnancy Category B: There are no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, and because treatment of onychomycosis can be postponed until after pregnancy is completed, it is recommended that terbinafine hydrochloride not be initiated during pregnancy.  

Oral reproduction studies have been performed in rabbits and rats at doses up to 300 mg/kg/day (12x to 23x the MRHD, in rabbits and rats, respectively, based on BSA) and have revealed no evidence of impaired fertility or harm to the fetus due to terbinafine.

After oral administration, terbinafine is present in breast milk of nursing mothers. The ratio of terbinafine in milk to plasma is 7:1. Treatment with terbinafine hydrochloride is not recommended in nursing mothers.

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

Clinical studies of terbinafine tablets did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Terbinafine is an allylamine antifungal [see Clinical Pharmacology (12.4)].

The pharmacodynamics of terbinafine hydrochloride is unknown.

Following oral administration, terbinafine is well absorbed (>70%) and the bioavailability of terbinafine tablets as a result of first-pass metabolism is approximately 40%. Peak plasma concentrations of 1 μg/mL appear within 2 hours after a single 250 mg dose; the AUC (area under the curve) is approximately 4.56 μg.h/mL. An increase in the AUC of terbinafine of less than 20% is observed when terbinafine tablets are administered with food.  

In plasma, terbinafine is >99% bound to plasma proteins and there are no specific binding sites. At steady-state, in comparison to a single dose, the peak concentration of terbinafine is 25% higher and plasma AUC increases by a factor of 2.5; the increase in plasma AUC is consistent with an effective half-life of ~36 hours. Terbinafine is distributed to the sebum and skin. A terminal half-life of 200-400 hours may represent the slow elimination of terbinafine from tissues such as skin and adipose. Prior to excretion, terbinafine is extensively metabolized by at least seven CYP isoenzymes with major contributions from CYP2C9, CYP1A2, CYP3A4, CYP2C8 and CYP2C19. No metabolites have been identified that have antifungal activity similar to terbinafine. Approximately 70% of the administered dose is eliminated in the urine.

In patients with renal impairment (creatinine clearance <50 mL/min) or hepatic cirrhosis, the clearance of terbinafine is decreased by approximately 50% compared to normal volunteers. No effect of gender on the blood levels of terbinafine was detected in clinical trials. No clinically relevant age-dependent changes in steady-state plasma concentrations of terbinafine have been reported.

Terbinafine, an allylamine antifungal, inhibits biosynthesis of ergosterol, an essential component of fungal cell membrane, via inhibition of squalene epoxidase enzyme. This results in fungal cell death primarily due to the increased membrane permeability mediated by the accumulation of high concentrations of squalene but not due to ergosterol deficiency. Depending on the concentration of the drug and the fungal species test in vitro, terbinafine hydrochloride may be fungicidal. However, the clinical significance of in vitro data is unknown.  

Terbinafine has been shown to be active against most strains of the following microorganisms both in vitro and in clinical infections:

Trichophyton mentagrophytes

Trichophyton rubrum

 The following in vitro data are available, but their clinical significance is unknown. In vitro, terbinafine exhibits satisfactory MIC’s against most strains of the following microorganisms; however, the safety and efficacy of terbinafine in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials:

Candida albicans

Epidermophyton floccosum

Scopulariopsis brevicaulis

In a 28-month oral carcinogenicity study in rats, an increase in the incidence of liver tumors was observed in males at the highest dose tested, 69 mg/kg/day [2x the Maximum Recommended Human Dose (MRHD) based on AUC comparisons of the parent terbinafine]; however, even though dose-limiting toxicity was not achieved at the highest tested dose, higher doses were not tested.

The results of a variety of in vitro (mutations in E. coli and S. typhimurium, DNA repair in rat hepatocytes, mutagenicity in Chinese hamster fibroblasts, chromosome aberration and sister chromatid exchanges in Chinese hamster lung cells), and in vivo (chromosome aberration in Chinese hamsters, micronucleus test in mice) genotoxicity tests gave no evidence of a mutagenic or clastogenic potential.  

Oral reproduction studies in rats at doses up to 300 mg/kg/day (approximately 12x the MRHD based on body surface area comparisons, BSA) did not reveal any specific effects on fertility or other reproductive parameters. Intravaginal application of terbinafine hydrochloride at 150 mg/day in pregnant rabbits did not increase the incidence of abortions or premature deliveries nor affect fetal parameters.

A wide range of in vivo studies in mice, rats, dogs, and monkeys, and in vitro studies using rat, monkey, and human hepatocytes suggest that peroxisome proliferation in the liver is a rat-specific finding. However, other effects, including increased liver weights and APTT, occurred in dogs and monkeys at doses giving Css trough levels of the parent terbinafine 2-3x those seen in humans at the MRHD. Higher doses were not tested.