Treatment of Onychomycosis
Oral terbinafine 250 mg daily is the first-line treatment for dermatophyte onychomycosis: 6 weeks for fingernails and 12-16 weeks for toenails. 1
Treatment Algorithm by Disease Severity
Mild Onychomycosis (<20% nail involvement, distal/superficial)
- Topical monotherapy: Amorolfine 5% lacquer once or twice weekly for 6-12 months 1
- Alternative: Efinaconazole 10% solution (if available) 2, 3
- Ciclopirox 8% lacquer daily for up to 48 weeks is less effective but acceptable when systemic therapy is contraindicated 1
Moderate Onychomycosis (20-60% nail involvement)
- Combination therapy recommended: Oral terbinafine PLUS topical amorolfine 1
- This approach increases cure rates beyond monotherapy alone
Severe Onychomycosis (>60% nail involvement, matrix involvement, or multiple nails)
Oral Antifungal Selection
Terbinafine is superior to itraconazole with complete cure rates of 55% vs 26% at 72 weeks, and significantly lower relapse rates (23% vs 53%) at 5-year follow-up 1. This superiority is based on higher efficacy, better tolerability, and fewer drug interactions.
Second-line oral options:
Itraconazole: 200 mg daily for 12 weeks continuous, OR pulse therapy 400 mg daily for 1 week per month (2 pulses for fingernails, 3 for toenails) 1
- Use when terbinafine is contraindicated or for non-dermatophyte infections
- Caution: Heart failure risk, hepatotoxicity, extensive drug interactions
Fluconazole: 150-450 mg weekly for 3 months (fingernails) or ≥6 months (toenails) 1
- Useful alternative when terbinafine and itraconazole are not tolerated
- Requires dose adjustment in renal impairment
Critical Monitoring Requirements
Before starting terbinafine:
- Baseline liver function tests and complete blood count in patients with:
- History of heavy alcohol consumption
- Hepatitis or liver disease
- Haematological abnormalities
- All children (as unlicensed in pediatrics) 1
Before starting itraconazole:
- Monitor hepatic function tests in patients with pre-existing abnormalities, continuous therapy >1 month, or concomitant hepatotoxic drugs 1
Before starting fluconazole:
- Baseline liver function tests and full blood count
- Monitor LFTs during high-dose or prolonged therapy 1
Important Contraindications
Terbinafine: Active or chronic liver disease, severe renal impairment 1
Itraconazole: Heart failure (can precipitate or worsen), hepatotoxicity 1
Fluconazole: Hepatic impairment, renal impairment (requires dose adjustment) 1
Common Pitfalls to Avoid
Permanent taste disturbance: Warn all patients starting terbinafine that taste disturbance, though rare, can be permanent 1
Psoriasis exacerbation: Terbinafine can aggravate psoriasis and cause subacute lupus-like syndrome 1
Drug interactions with itraconazole: Extensive CYP3A4 interactions make itraconazole problematic with many medications 1
Inadequate treatment duration: Re-evaluate patients 3-6 months after treatment initiation; give further treatment if disease persists 1
Treating without mycological confirmation: Approximately half of nail dystrophies are non-fungal 4
Pediatric Dosing (Ages 1-12 years)
Terbinafine (first-line):
- <20 kg: 62.5 mg daily
- 20-40 kg: 125 mg daily
40 kg: 250 mg daily
- Duration: 6 weeks (fingernails), 12 weeks (toenails) 1
Itraconazole pulse therapy: 5 mg/kg daily for 1 week per month (2 pulses for fingernails, 3 for toenails) 1
Why Terbinafine is Preferred
The evidence strongly favors terbinafine based on:
- Higher complete cure rates (55% vs 26% for itraconazole) 1
- Lower long-term relapse (23% vs 53%) 1
- Minimal drug interactions (only CYP2D6 substrates) 1
- Fungicidal activity against dermatophytes vs fungistatic azoles 1
- Persistent nail levels for 6 months post-treatment 1
The British Association of Dermatologists gives both terbinafine and itraconazole Grade A recommendations, but explicitly states terbinafine is "generally preferred" based on superior efficacy and tolerability 1.