What is the best first‑line treatment for fingernail onychomycosis in a child?

Oral Terbinafine is the Best First-Line Treatment for Fingernail Onychomycosis in Children

For fingernail fungal infection in a child, oral terbinafine is the preferred first-line treatment, dosed by weight (62.5 mg daily if <20 kg, 125 mg daily if 20-40 kg, or 250 mg daily if >40 kg) for 6 weeks. 1, 2

Weight-Based Dosing Algorithm for Terbinafine

• Children weighing <20 kg: 62.5 mg daily for 6 weeks 1, 2
• Children weighing 20-40 kg: 125 mg daily for 6 weeks 1, 2
• Children weighing >40 kg: 250 mg daily for 6 weeks 1, 2

The British Association of Dermatologists guidelines establish terbinafine as the preferred agent over itraconazole due to superior efficacy and tolerability, despite both being listed as first-line options. 1, 2 In adult comparative data that inform pediatric practice, terbinafine achieved 46% long-term mycological cure versus only 13% for itraconazole, with substantially lower relapse rates (23% vs 53%). 2

Pre-Treatment Requirements

Before starting terbinafine, you must obtain:

• Mycological confirmation of fungal infection (KOH preparation or culture) to avoid treating non-fungal nail dystrophies 2
• Baseline liver function tests (ALT, AST) 2, 3
• Complete blood count 2, 3

Terbinafine is not FDA-licensed for pediatric use, making baseline laboratory monitoring particularly important despite off-label efficacy and safety data. 2

Alternative First-Line Option: Pulse Itraconazole

If terbinafine is contraindicated or not tolerated, pulse itraconazole at 5 mg/kg per day for 1 week per month for 2 total pulses (2 months) is the alternative first-line choice for fingernails. 1, 2

• Administer with food in an acidic gastric environment to optimize absorption 2
• Monitor hepatic function if pre-existing liver abnormalities exist or if continuous therapy exceeds one month 2

Why Children Respond Better Than Adults

Children achieve higher cure rates and faster responses than adults because: 1

• Thinner nail plates allow better drug penetration 1, 4
• Faster nail growth accelerates clearance of infected nail 1, 4

Second-Line Systemic Options (When Both Terbinafine and Itraconazole Fail)

Agent	Dose	Duration for Fingernails	Key Monitoring
Fluconazole	3-6 mg/kg once weekly	12-16 weeks	Baseline LFT and CBC [2]
Griseofulvin	10 mg/kg/day (max 500 mg)	Longer courses required	Take with fatty food; only 30-40% cure rate [2,5]

Fluconazole is reserved for cases where both terbinafine and itraconazole are contraindicated or not tolerated. 2 Griseofulvin is no longer recommended as first-line due to long treatment duration and low efficacy. 1

Topical Therapy Considerations

Topical agents are generally insufficient as monotherapy for fingernail onychomycosis, but may be considered in specific circumstances: 1

• Efinaconazole 10% solution is FDA-approved for children ≥6 years, applied daily for 24-48 weeks 6, 7, 4
• Tavaborole 5% solution is FDA-approved for children ≥6 years 4
• Ciclopirox 8% lacquer is FDA-approved for children ≥12 years 4

However, the British Association of Dermatologists notes there are no clinical trials demonstrating efficacy of topical therapies for pediatric onychomycosis, and systemic therapy remains more effective. 1 Topical agents require no baseline laboratory testing and have minimal systemic absorption. 6

Critical Safety Monitoring During Treatment

Common adverse effects of terbinafine include: 2, 3

• Headache and gastrointestinal upset (most frequent) 2
• Rash, pruritus, urticaria 2
• Rare but serious: taste disturbance (can be permanent), hepatotoxicity 2, 3

Monitoring strategy:

• For standard 6-week fingernail treatment, routine repeat LFTs are not required unless clinical symptoms develop 3
• Discontinue immediately if biochemical liver injury or progressive skin rash develops 3
• Monitor for at least 48 weeks from treatment start to detect potential relapse 2

Contraindications to Terbinafine

Absolute contraindications: 3

• Renal impairment (creatinine clearance ≤50 mL/min) 3
• Active or chronic liver disease 3

For children with renal impairment, topical therapy (amorolfine or ciclopirox) is the preferred approach, or consider itraconazole if hepatic function is normal. 3

Family and Concomitant Infection Management

Examine the child for: 2

• Concomitant tinea capitis and tinea pedis 2

Screen parents and siblings for: 2

• Onychomycosis and tinea pedis (family transmission is common) 2

Prevention measures: 2

• Decontaminate or replace contaminated footwear 2
• Apply antifungal powders inside shoes regularly 2
• Keep nails short and clean 2
• Avoid sharing nail clippers with infected family members 2

Clinical Pitfalls to Avoid

• Do not start treatment without mycological confirmation – many nail dystrophies mimic onychomycosis but are not fungal 2
• Do not use griseofulvin as first-line – it has only 30% efficacy and requires prolonged treatment 1, 5
• Do not skip baseline laboratory testing – terbinafine is unlicensed in children and requires safety monitoring 2
• Do not stop monitoring at treatment completion – follow for 48 weeks to identify relapse 2