What is the recommended dose of terbinafine (antifungal medication) for a 39-year-old female with normal renal function?

Terbinafine Dosing for a 39-Year-Old Female

For a 39-year-old female with normal renal function, the recommended dose of terbinafine is 250 mg orally once daily, with treatment duration determined by the site of infection: 1-2 weeks for tinea pedis, 6 weeks for fingernail onychomycosis, or 12-16 weeks for toenail onychomycosis. 1, 2, 3

Standard Dosing by Indication

Dermatophyte Skin Infections (Tinea Pedis, Corporis, Cruris)

• Terbinafine 250 mg daily for 1-2 weeks achieves mycological cure rates of 80-90% for cutaneous dermatophyte infections 1
• The British Association of Dermatologists recommends this as first-line treatment for dermatophyte foot infections, with superior efficacy compared to other antifungals 1
• Treatment can be taken with or without food, as food increases absorption by less than 20% 3

Onychomycosis (Nail Infections)

• Fingernail infections: 250 mg daily for 6 weeks 2
• Toenail infections: 250 mg daily for 12-16 weeks 1, 2
• Continuous daily dosing is significantly more effective than intermittent pulsed regimens and remains the optimal therapy 4
• The British Association of Dermatologists identifies terbinafine as the oral antifungal of choice for diabetic patients with onychomycosis due to low risk of drug interactions and hypoglycemia 5

Important Clinical Considerations

Baseline Monitoring Requirements

• Liver function tests and complete blood count are recommended for patients with history of heavy alcohol consumption, pre-existing liver disease, or history of hepatitis 1
• Active or chronic liver disease is an absolute contraindication to terbinafine 2
• In patients with renal impairment (creatinine clearance ≤50 mL/min), terbinafine use has not been adequately studied and clearance is decreased by approximately 50% 3

Drug Interactions to Avoid

• Rifampin increases terbinafine clearance by 100%, potentially reducing efficacy 3
• Cimetidine decreases clearance by 33%, potentially increasing exposure 3
• Fluconazole increases terbinafine exposure by 52-69% (Cmax and AUC), and other dual CYP2C9/CYP3A4 inhibitors like ketoconazole and amiodarone may have similar effects 3
• Monitor prothrombin times if co-administered with warfarin, as spontaneous reports suggest potential interactions 3

Safety Profile

• Gastrointestinal disturbances account for 49% of reported side effects, and dermatological reactions for 23% 1
• Rare but serious adverse events include hepatotoxicity, taste disturbance (which can be permanent), Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS syndrome 2
• Overall, terbinafine is well tolerated with only 5.3% of patients reporting adverse effects in post-marketing surveillance 6

Special Populations

• Pregnancy: Category B, but treatment should be postponed until after pregnancy as onychomycosis treatment is not urgent 3
• Nursing mothers: Terbinafine is present in breast milk with a milk-to-plasma ratio of 7:1; treatment is not recommended during breastfeeding 3
• Elderly patients: Dose selection should be cautious, starting at the low end of the dosing range due to potential decreased hepatic, renal, or cardiac function 3

Mechanism Supporting Efficacy

• Terbinafine has a fungicidal mechanism of action against dermatophytes through inhibition of squalene epoxidase, leading to ergosterol depletion and squalene accumulation 1, 3
• The drug is highly lipophilic and keratophilic, remaining in stratum corneum, sebum, nails, and hair for months after stopping medication 7
• Mycological cure rates often improve after treatment cessation due to this residual tissue effect 8