What is the recommended dose and frequency of Terbinafine (antifungal medication)?

Terbinafine Dosing and Frequency

The standard adult dose of terbinafine is 250 mg once daily, with treatment duration of 6 weeks for fingernail onychomycosis and 12 weeks for toenail onychomycosis. 1

Standard Adult Dosing by Indication

Onychomycosis (Nail Infections)

• Fingernail infections: 250 mg once daily for 6 weeks 2, 3, 4, 1
• Toenail infections: 250 mg once daily for 12 weeks (up to 16 weeks for severe cases) 2, 3, 4, 1
• The British Association of Dermatologists provides this as a Grade A recommendation with Level 1+ evidence 4

Tinea Pedis (Foot Fungal Infections)

• 250 mg once daily for 1-2 weeks achieves mycological cure rates of approximately 80-90% 2

Administration Details

• Can be taken with or without food - absorption is not affected by food intake 4, 1
• Once daily dosing provides convenience and improves compliance 4, 1

Pediatric Dosing

For children with onychomycosis (though not FDA-approved for this indication):

• Children <20 kg: 62.5 mg daily 4
• Children 20-40 kg: 125 mg daily 4
• Children >40 kg: 250 mg daily (adult dose) 4
• Duration: 6 weeks for fingernails, 12 weeks for toenails 4

Important Caveat: Pulse Therapy NOT Recommended

While some studies have explored pulse dosing regimens (500 mg daily for 1 week per month), continuous daily dosing remains superior and is the recommended approach:

• Pulse therapy showed significantly lower complete cure rates compared to continuous dosing in large trials 5
• The FDA-approved regimen is continuous daily dosing only 1
• Continuous treatment with terbinafine remains the optimal therapy for onychomycosis 5

Pre-Treatment Requirements

Mandatory baseline testing before initiating therapy:

• Liver function tests (ALT and AST) for all patients 3, 4, 1
• Complete blood count (CBC) especially for patients with history of hepatitis, heavy alcohol use, or hematological abnormalities 4
• Mycological confirmation (microscopy and culture) to confirm dermatophyte infection 1

Absolute Contraindications

Do not prescribe terbinafine in:

• Active or chronic liver disease 3, 4, 1
• History of allergic reaction to oral terbinafine (risk of anaphylaxis) 1
• Lupus erythematosus 3, 4

Monitoring During Treatment

• Re-evaluate patients 3-6 months after treatment initiation to assess response 3, 4
• More vigilant liver function monitoring is required for patients with pre-existing liver disease, concomitant hepatotoxic medications, or continuous therapy exceeding one month 3
• If neutrophil count drops to ≤1,000 cells/mm³, discontinue terbinafine immediately 1

Critical Safety Warnings

Discontinue terbinafine immediately if:

• Liver injury develops - can progress to liver failure requiring transplant or causing death 1
• Taste disturbance occurs - may be severe, prolonged, or permanent 3, 1
• Smell disturbance occurs - may be prolonged or permanent 1
• Severe skin reactions develop including Stevens-Johnson syndrome, toxic epidermal necrolysis, or DRESS syndrome 4, 1
• Depressive symptoms emerge 1

Pharmacokinetic Rationale for Duration

• Terbinafine persists in the nail for 6 months after treatment completion due to its long half-life and lipophilic properties 4
• This allows for continued fungicidal activity even after stopping therapy, explaining why mycological cure rates often improve post-treatment 4
• This pharmacokinetic profile supports the relatively short treatment durations compared to older antifungals 4

Drug Interactions

Terbinafine has minimal drug interactions compared to azole antifungals, making it safer for patients on multiple medications 3, 4

Primary interaction concern:

• Drugs metabolized by cytochrome P450 2D6 including certain antidepressants, beta-blockers, and antiarrhythmics 3, 4, 1
• Also interacts with desipramine, cimetidine, fluconazole, cyclosporine, rifampin, and caffeine 1

Common Adverse Effects

The most frequently reported side effects include:

• Gastrointestinal disturbances (49% of reported side effects): diarrhea, dyspepsia, nausea, abdominal pain, flatulence 2, 1
• Dermatological reactions (23% of reported side effects): rash, pruritus 2, 1
• Headache 1
• Liver enzyme abnormalities 1
• Serious adverse events occur in only 0.04% of patients 4

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 and griseofulvin for dermatophyte onychomycosis 2, 3, 4
• Better tolerability and lower drug interaction potential than azole antifungals 3, 4
• Preferred for diabetic patients due to low risk of drug interactions and hypoglycemia 2