What is the first-line treatment for a 9-year-old child with confirmed onychomycosis?

Treatment for Onychomycosis in a 9-Year-Old Child

Oral terbinafine is the first-line treatment for a 9-year-old child with confirmed onychomycosis, dosed at 125 mg daily (for 20-40 kg body weight) or 250 mg daily (for >40 kg) for 12 weeks for toenails or 6 weeks for fingernails. 1, 2, 3

Weight-Based Dosing Algorithm for Terbinafine

The dosing is straightforward and based solely on the child's weight 1:

• <20 kg: 62.5 mg daily
• 20-40 kg: 125 mg daily
• >40 kg: 250 mg daily

For a typical 9-year-old (usually 20-40 kg), the dose would be 125 mg daily. 1

Treatment Duration

• Fingernail infection: 6 weeks 1, 2
• Toenail infection: 12 weeks 1, 2, 3

Why Terbinafine Over Itraconazole

While both terbinafine and itraconazole are listed as first-line options with equal strength of recommendation in pediatric guidelines, terbinafine is generally preferred due to superior efficacy and tolerability 1, 2. In adults, terbinafine demonstrates 46% long-term mycological cure versus only 13% with itraconazole, with significantly lower relapse rates (23% vs 53%). 1 Children achieve even higher cure rates than adults due to thinner nail plates and faster nail growth. 2, 4, 5

Critical Pre-Treatment Requirements

Before initiating terbinafine, you must obtain 1:

• Baseline liver function tests
• Complete blood count

This monitoring is essential because terbinafine is unlicensed for pediatric use, despite being the preferred agent. 1

Mycological Confirmation is Mandatory

Never treat without mycological confirmation through potassium hydroxide preparation with microscopy and/or fungal culture to avoid treating non-fungal nail dystrophies. 2, 3, 5 This is particularly important in children where onychomycosis is less common than in adults. 6, 7

Concurrent Management Strategies

Examine the Entire Family Unit

You must examine parents and siblings for onychomycosis and tinea pedis, as family transmission is extremely common. 2, 3 Check the affected child for concomitant tinea capitis and tinea pedis. 2, 3

Add Topical Antifungal for Tinea Pedis

If tinea pedis is present (which commonly coexists), add topical terbinafine 1% cream twice daily for 1 week or another topical antifungal. 3, 8 Failing to treat concurrent foot infection serves as a reservoir for reinfection. 8

Environmental Decontamination

Implement these prevention measures concurrently with treatment 2, 3:

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

Alternative First-Line Option: Itraconazole

If terbinafine is contraindicated or not tolerated, use itraconazole pulse therapy at 5 mg/kg per day for 1 week per month 1:

• Fingernails: 2 pulses (2 months total)
• Toenails: 3 pulses (3 months total)

Itraconazole requires monitoring of hepatic function tests in patients with pre-existing abnormalities or when using continuous therapy for more than one month. 1 It must be taken with food and in an acidic pH environment for optimal absorption. 1

Second-Line Options

Fluconazole

Use only when terbinafine and itraconazole are contraindicated or not tolerated 1, 2:

• Dose: 3-6 mg/kg once weekly
• Duration: 12-16 weeks for fingernails, 18-26 weeks for toenails
• Requires baseline liver function tests and complete blood count 1

Griseofulvin

Another second-line option 1:

• Dose: 10 mg/kg per day (maximum 500 mg)
• Must be taken with fatty food to increase absorption
• Has lower efficacy (30-40% cure rates) and requires longer treatment duration 1

Topical Therapy Considerations

While topical agents like efinaconazole 10% solution and tavaborole 5% solution are FDA-approved for children ≥6 years, they are less effective than oral therapy. 6, 7, 5 However, children respond better to topical monotherapy than adults due to thinner, faster-growing nails. 4, 5

Topical therapy may be considered for 6, 7, 5:

• Mild to moderate disease
• Patients unable to tolerate systemic therapy
• Combination with oral therapy for enhanced efficacy

Common Adverse Effects to Warn About

Terbinafine is generally well tolerated, but counsel families about 1:

• Headache and gastrointestinal upset (most common)
• Taste disturbance (very rare but can be permanent)
• Rash, pruritus, urticaria
• Can aggravate psoriasis or cause subacute lupus-like syndrome 1

Follow-Up and Monitoring

Monitor for at least 48 weeks from treatment start to identify potential relapse. 2, 3 Re-evaluate 3-6 months after treatment initiation, and provide further treatment if disease persists. 1

Critical Pitfall to Avoid

The most common cause of treatment failure is failing to treat all infected family members simultaneously and neglecting to address contaminated footwear, which leads to reinfection. 8 This is more important than the choice of antifungal agent itself.