What is the recommended dosing for Terbinafine (antifungal medication)?

Terbinafine Dosing

For onychomycosis, prescribe terbinafine 250 mg once daily for 6 weeks for fingernail infections and 12 weeks (up to 16 weeks for severe cases) for toenail infections. 1, 2, 3

Standard Adult Dosing by Indication

Onychomycosis (Nail Infections)

• Fingernail onychomycosis: 250 mg once daily for 6 weeks 1, 2, 3
• Toenail onychomycosis: 250 mg once daily for 12-16 weeks 1, 2, 4, 3
• Re-evaluate patients 3-6 months after treatment initiation; provide additional treatment if disease persists 1, 4
• The drug persists in the nail for 6 months after treatment completion due to its long half-life and lipophilic properties, allowing continued fungicidal activity 1, 2

Tinea Capitis (Scalp Ringworm) - Pediatric Dosing

• <20 kg: 62.5 mg daily for 2-4 weeks 5, 2
• 20-40 kg: 125 mg daily for 2-4 weeks 5, 2
• >40 kg: 250 mg daily for 2-4 weeks 5, 2
• Critical caveat: Terbinafine is highly effective against Trichophyton species but significantly less effective against Microsporum species; griseofulvin is superior for Microsporum infections 2

Other Dermatophyte Infections (Tinea Corporis/Cruris, Tinea Pedis)

• 250 mg once daily for 2-4 weeks achieves mycological cure in >80% of patients 6, 7
• Can be taken with or without food as absorption is not affected 2

Pre-Treatment Requirements

Obtain baseline laboratory tests before initiating therapy:

• Liver function tests (LFTs) - mandatory 2, 4, 3
• Complete blood count (CBC) - particularly important in patients with history of hepatitis, heavy alcohol use, or hematological abnormalities 1, 2
• Baseline monitoring should also be considered for children, as terbinafine is not licensed for pediatric onychomycosis 1

Absolute Contraindications

Do not prescribe terbinafine in:

• Active or chronic liver disease 1, 2, 4, 3
• History of allergic reaction to oral terbinafine (risk of anaphylaxis) 2, 3
• Lupus erythematosus 2, 4

Critical Safety Warnings

Hepatotoxicity

• Liver failure, sometimes leading to liver transplant or death, has occurred with oral terbinafine 3
• Discontinue immediately if liver injury develops 3
• More vigilant monitoring required in patients with pre-existing liver disease, concomitant hepatotoxic medications, or continuous therapy exceeding one month 4

Severe Cutaneous Reactions

• Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, exfoliative dermatitis, bullous dermatitis, and DRESS syndrome have been reported 1, 2, 3
• Discontinue immediately if signs or symptoms of drug reaction occur 3

Sensory Disturbances

• Taste disturbance (including complete taste loss) can be severe, prolonged, or permanent; discontinue if this occurs 3
• Patients must be warned that taste disturbance, though rare, can be permanent 1
• Smell disturbance (including complete loss of smell) may be prolonged or permanent; discontinue if this occurs 3

Hematologic Toxicity

• Severe neutropenia has been reported; discontinue if neutrophil count ≤1,000 cells/mm³ 3

Psychiatric Effects

• Depressive symptoms have been reported; monitor for development of depression 3

Drug Interactions

Terbinafine has minimal drug-drug interactions compared to azole antifungals, making it safer for patients on multiple medications. 1, 2, 4

• The only potentially significant interaction is with drugs metabolized by cytochrome P450 2D6 isoenzyme 1, 5, 2
• This includes certain antidepressants, beta-blockers, and antiarrhythmics 2
• Unlike azoles, terbinafine does not significantly interact with most other medications 1

Common Adverse Effects

The most common side effects (>2% of patients) include 3:

• Gastrointestinal complaints (49%): nausea, diarrhea, dyspepsia, abdominal pain, flatulence 1
• Dermatological events (23%): rash, pruritus, urticaria, eczema 1
• Headache 3
• Liver enzyme abnormalities 3
• Incidence of serious adverse events is only 0.04% 1

Why Terbinafine is First-Line

Terbinafine should be considered first-choice therapy for dermatophyte onychomycosis based on superior efficacy and tolerability. 1

• Terbinafine is fungicidal against dermatophytes with very low minimum inhibitory concentrations (approximately 0.004 μg/mL) 1, 2, 4
• In the landmark L.I.ON. study, complete cure rates at 72 weeks were approximately twice as high with terbinafine (55%) versus pulsed itraconazole (26%) 1
• At 5-year follow-up, mycological cure without re-treatment was 46% for terbinafine versus 13% for itraconazole 1
• Mycological and clinical relapse rates were significantly lower with terbinafine (23% and 21%) compared to itraconazole (53% and 48%) 1
• Itraconazole remains the next best alternative when terbinafine is contraindicated 1