Treatment of Tinea Unguium (Onychomycosis)
Oral terbinafine 250 mg daily is the first-line treatment for tinea unguium, given for 6 weeks for fingernails and 12-16 weeks for toenails, based on its superior efficacy, tolerability, and lower relapse rates compared to all alternatives. 1
First-Line Therapy: Terbinafine
Dosing and Duration:
- Toenails: 250 mg daily for 12-16 weeks
- Fingernails: 250 mg daily for 6 weeks
- Re-evaluate patients 3-6 months after treatment initiation; provide additional treatment if disease persists 1
Why Terbinafine is Superior:
The evidence strongly favors terbinafine over itraconazole. A large multicenter trial of 508 patients demonstrated complete cure rates of 55% with terbinafine versus only 26% with pulsed itraconazole at 72 weeks. More importantly, long-term follow-up at 5 years showed mycological cure in 46% of terbinafine-treated patients versus only 13% with itraconazole. Relapse rates were dramatically lower with terbinafine (23% clinical, 21% mycological) compared to itraconazole (48% clinical, 53% mycological) 1.
Baseline Monitoring Requirements
Obtain baseline liver function tests and complete blood count in patients with:
- History of heavy alcohol consumption
- Known hepatitis or liver disease
- Hematological abnormalities
- Children (as terbinafine is not licensed for pediatric onychomycosis) 1
Contraindication: Do not use terbinafine in patients with active or chronic liver disease 1
Second-Line Therapy: Itraconazole
Use when terbinafine is contraindicated or not tolerated.
Dosing Options:
- Continuous: 200 mg daily for 12 weeks
- Pulse therapy: 400 mg daily for 1 week per month
- 2 pulses for fingernails
- 3 pulses for toenails 1
Itraconazole has more drug-drug interactions than terbinafine due to cytochrome P450 inhibition, making it less desirable despite being effective 1.
Third-Line Therapy: Fluconazole
Use only when both terbinafine and itraconazole cannot be used.
Dosing:
- Fingernails: 450 mg weekly for 3 months
- Toenails: 450 mg weekly for at least 6 months 1
Fluconazole is less effective than both terbinafine and itraconazole (mycological cure rates 47-62% for toenails), but the once-weekly dosing may improve compliance. Adverse effects leading to discontinuation occur in 20% at 150 mg weekly, increasing to 58% at higher doses (300-450 mg) 1.
Special Consideration: Candida Onychomycosis
If Candida species are identified (not dermatophytes), the treatment hierarchy reverses:
First-line for Candida: Itraconazole
- 200 mg daily OR 400 mg daily for 1 week per month (pulse)
- Minimum 4 weeks for fingernails, 12 weeks for toenails 1
Alternative for Candida: Fluconazole
- 50 mg daily OR 300 mg weekly
- Same duration as itraconazole 1
Terbinafine is less effective against Candida and requires prolonged treatment (48 weeks) to achieve acceptable cure rates 1.
Critical Safety Warnings
Warn all patients about:
- Permanent taste disturbance: Rare but can be irreversible with terbinafine 1
- Serious hepatotoxicity: Rare reports of Stevens-Johnson syndrome and toxic epidermal necrolysis with terbinafine 1
- Common side effects: Gastrointestinal symptoms (49%) and dermatological reactions (23%) with terbinafine 1
Common Pitfalls to Avoid
- Insufficient treatment duration: Toenail infections require 12-16 weeks, not the 6 weeks used for fingernails
- Failure to confirm diagnosis: Always obtain mycological confirmation before starting systemic therapy, as other conditions (psoriasis, trauma-related dystrophy) can mimic onychomycosis 2
- Not monitoring for relapse: Re-evaluate 3-6 months post-treatment, as the nail continues to grow out and fungus may persist 1
- Using combination antifungal-corticosteroids: Avoid these to prevent resistance and treatment failure 2
Drug Interaction Considerations
Terbinafine has minimal drug interactions, affecting only drugs metabolized by cytochrome P450 2D6. Itraconazole and fluconazole have more extensive interactions through cytochrome P450 inhibition, requiring careful medication review before prescribing 1.