What is the recommended dosage and frequency of terbinafine (antifungal medication) for treating nail fungus?

Terbinafine Dosing for Nail Fungus

For toenail fungus, take terbinafine 250 mg once daily for 12 weeks; for fingernail fungus, take 250 mg once daily for 6 weeks. 1, 2, 3

Standard Treatment Regimen

Toenail Onychomycosis

• Take 250 mg once daily for 12 weeks continuously 1, 2, 3
• Some guidelines suggest extending treatment to 12-16 weeks for more severe toenail infections 4
• The medication can be taken with or without food, as absorption is not affected by food intake 2

Fingernail Onychomycosis

• Take 250 mg once daily for 6 weeks 1, 2, 3
• This shorter duration is sufficient because fingernails grow faster than toenails 1

Why This Continuous Daily Dosing Works

• Terbinafine persists in the nail for up to 6 months (30 weeks) after treatment completion due to its long half-life and lipophilic properties, allowing continued fungicidal activity even after you stop taking it 2, 5
• Nail terbinafine concentrations are detected within 1 week of starting therapy 5
• This pharmacokinetic profile explains why you see continued improvement for months after finishing the medication 2, 5

Important Pre-Treatment Requirements

Before starting terbinafine, you must:

• Confirm the diagnosis with microscopy and culture—never start treatment without mycological confirmation 1
• Obtain baseline liver function tests (LFTs) and complete blood count (CBC) 2, 4, 6
• Check for contraindications, particularly active or chronic liver disease and lupus erythematosus 2, 4, 3

Follow-Up Timing

• Re-evaluate patients 3-6 months after starting treatment 4
• Allow at least 48 weeks (preferably 72 weeks) from treatment start to fully assess cure, as the nail needs time to grow out completely 1
• If disease persists at the 3-6 month evaluation, additional treatment may be needed 4

Why Terbinafine is First-Line

Terbinafine is superior to itraconazole for dermatophyte nail infections 1, 2, 4:

• Mycological cure rates at 72 weeks: 76-81% with terbinafine versus 38-49% with itraconazole 5
• Complete cure rates are approximately twice as high with terbinafine compared to intermittent itraconazole 5
• At 5-year follow-up, terbinafine maintained superior cure rates (35% vs 14% complete cure) with lower relapse rates (23% vs 53% mycological relapse) 5

Common Pitfall to Avoid

Do not use pulse or intermittent dosing regimens for terbinafine—unlike itraconazole, which is licensed for pulse therapy, terbinafine is approved and most effective when given as continuous daily therapy 1, 3. While one small study explored quarterly pulse dosing 7, this is not the standard of care and lacks the robust evidence supporting continuous daily dosing 1, 2, 3.

Safety Monitoring During Treatment

• More vigilant LFT monitoring is needed in patients with pre-existing liver disease, concomitant hepatotoxic medications, continuous therapy beyond one month, or history of heavy alcohol consumption 4, 6
• Discontinue immediately if signs of liver injury, taste disturbance, smell disturbance, severe skin reactions, or depressive symptoms develop 3
• If neutrophil count drops to ≤1,000 cells/mm³, discontinue terbinafine 3

Drug Interaction Advantage

• Terbinafine has minimal drug-drug interactions compared to azole antifungals (like itraconazole or fluconazole), making it safer for patients on multiple medications 2, 4, 6
• The main interaction concern is with drugs metabolized by cytochrome P450 2D6 (certain antidepressants, beta-blockers, antiarrhythmics) 2, 4, 6