Terbinafine Dosing
For adults, terbinafine is dosed at 250 mg once daily, with treatment duration of 6 weeks for fingernail onychomycosis and 12 weeks (up to 16 weeks for severe cases) for toenail onychomycosis. 1, 2
Adult Dosing by Indication
Onychomycosis (Nail Infections)
- Fingernail infections: 250 mg once daily for 6 weeks 1, 2, 3
- Toenail infections: 250 mg once daily for 12-16 weeks 1, 2, 4, 3
- Food does not affect absorption, so terbinafine can be taken with or without meals 2
The British Association of Dermatologists designates terbinafine as first-line treatment for dermatophyte onychomycosis with a strength of recommendation A and level of evidence 1+, generally preferred over itraconazole due to superior efficacy and lower relapse rates 1, 2.
Tinea Pedis (Athlete's Foot)
- 250 mg once daily for 1-2 weeks achieves mycological cure rates of 80-90% 5
Important Timing Consideration
- The optimal clinical effect occurs months after treatment completion due to the time required for healthy nail outgrowth 3
- Terbinafine persists in nails for 6 months after treatment cessation, allowing continued fungicidal activity 2
- Re-evaluate patients 3-6 months after treatment initiation; if disease persists, additional treatment can be started immediately without waiting 2, 4
Pediatric Dosing
Weight-Based Dosing for Onychomycosis
Treatment Duration in Children
Critical caveat: Terbinafine is not FDA-approved for pediatric onychomycosis, though it is the only oral antifungal licensed for use in children in some jurisdictions 1. Griseofulvin remains the only FDA-approved oral antifungal for pediatric onychomycosis at 10 mg/kg per day 1.
Pre-Treatment Requirements
Mandatory Baseline Testing
- Liver function tests (ALT and AST) 1, 2, 3
- Complete blood count 1, 2
- Mycological confirmation (KOH preparation and fungal culture) to confirm dermatophyte infection 3
These tests are particularly important in patients with:
- History of hepatitis or liver disease 1, 2
- Heavy alcohol consumption 1, 2
- Hematological abnormalities 1, 2
- Concomitant hepatotoxic medications 4
Ongoing Monitoring
- More vigilant liver function monitoring is required for patients receiving continuous therapy for more than one month 4
- Patients with pre-existing deranged liver function tests require monitoring throughout treatment 1
Absolute Contraindications
- Active or chronic liver disease 2, 4
- Lupus erythematosus 2, 4
- History of allergic reaction to oral terbinafine 4, 3
Common Adverse Effects and Warnings
Frequent Side Effects
- Gastrointestinal disturbances (49% of reported side effects): nausea, diarrhea, abdominal pain 1, 5
- Dermatological reactions (23% of reported side effects) 5
- Headache 1
- Taste disturbance 1
Serious Adverse Events (Rare)
- Hepatotoxicity: Patients must immediately report persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain, jaundice, dark urine, or pale stools 3
- Stevens-Johnson syndrome and toxic epidermal necrolysis: Discontinue immediately if hives, mouth sores, blistering/peeling skin, or facial swelling occur 2, 3
- Subacute lupus-like syndrome 1
- Psoriasis aggravation 1
Drug Interactions
Terbinafine has minimal drug-drug interactions compared to azole antifungals, making it safer for patients on multiple medications 2, 4. The primary interaction concern involves drugs metabolized by cytochrome P450 2D6, including:
Why Terbinafine is First-Line
- Fungicidal mechanism against dermatophytes with very low minimum inhibitory concentrations (approximately 0.004 μg/mL) 2, 4
- Superior efficacy compared to itraconazole for dermatophyte onychomycosis with higher cure rates and lower relapse rates 2, 4
- Minimal drug interactions compared to azole antifungals 2, 4
- Favorable safety profile with serious adverse events occurring in only 0.04% of patients 2
Important Limitation
Terbinafine is highly effective against Trichophyton species but significantly less effective against Microsporum species; griseofulvin is superior for Microsporum infections 2. For Candida onychomycosis, itraconazole is preferred over terbinafine due to broader antimicrobial coverage 1.
Special Populations
Pregnancy and Lactation
- Terbinafine should not be started during pregnancy without discussing with the physician 3
- The drug passes into breast milk and may harm the baby; discuss feeding options with the physician 3
Diabetic Patients
- Terbinafine is the oral antifungal of choice for diabetic patients with onychomycosis due to low risk of drug interactions and hypoglycemia 5