General
Terbinafine Hydrochloride Tablets are not recommended for patients with chronic or active liver disease. Before prescribing Terbinafine Hydrochloride Tablets, pre-existing liver disease should be assessed. Hepatotoxicity may occur in patients with and without pre-existing liver disease. Pretreatment serum transaminase (ALT and AST) tests are advised for all patients before taking Terbinafine Hydrochloride Tablets. Patients prescribed Terbinafine Hydrochloride 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 (see WARNINGS). Patients with these symptoms should discontinue taking oral terbinafine, and the patient's liver function should be immediately evaluated.
In patients with renal impairment (creatinine clearance ≤50 mL/ min), the use of terbinafine hydrochloride has not been adequately studied, and therefore, is not recommended (see CLINICAL PHARMACOLOGY, Pharmaco*kinetics).
During postmarketing experience, precipitation and exacerbation of cutaneous and systemic lupus erythematosus have been reported infrequently in patients taking terbinafine hydrochloride. Terbinafine hydrochloride therapy should be discontinued in patients with clinical signs and symptoms suggestive of lupus erythematosus.
Changes in the ocular lens and retina have been reported following the use of Terbinafine Hydrochloride Tablets in controlled trials. The clinical significance of these changes is unknown.
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. The clinical significance of this observation is unknown. However, in patients with known or suspected immunodeficiency, physicians should consider monitoring complete blood counts in individuals using Terbinafine Hydrochloride therapy for greater than six weeks.
Isolated 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.
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 Hydrochloride 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 Cmax 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 hydrochloride.
In vitro studies with human liver microsomes showed that terbinafine does not inhibit the metabolism of tolbutamide, ethinylestradiol, ethoxycoumarin, and cyclosporine.
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%.
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 Hydrochloride 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, theophyllines, phenytoins, thiazide diuretics, and calcium channel blockers.
Carcinogenesis, Mutagenesis, Impairment of Fertility
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. Intravagin*l 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.
Pregnancy
Pregnancy Category B
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. There are, however, 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.
Nursing Mothers
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.
Pediatric Use
The safety and efficacy of Terbinafine Hydrochloride Tablets have not been established in pediatric patients.
