What is the recommended initial evaluation and first‑line treatment for a pediatric patient with suspected toenail onychomycosis?

Toenail Fungus in Children: Initial Evaluation and First-Line Treatment

Always confirm the diagnosis with mycological testing (KOH microscopy and fungal culture) before initiating any treatment, then start oral terbinafine as first-line therapy using weight-based dosing for 12 weeks. 1

Initial Diagnostic Evaluation

Mycological Confirmation is Mandatory

• Never treat based on clinical appearance alone—this is the most common cause of treatment failure in the U.K. 1
• Obtain subungual debris from the most proximal part of the infection using a small dental scraper; scrape material from beneath the nail plate and from the nail bed if the nail is onycholytic 1
• Submit specimens for both KOH microscopy (to visualize fungal elements) and fungal culture on Sabouraud's glucose agar (to identify the specific organism) 1
• Only 50% of nail dystrophies are fungal in origin—psoriasis and trauma are common mimics that will not respond to antifungal therapy 1

Examine for Associated Infections

• Check the child for concomitant tinea pedis (present in 25% of pediatric onychomycosis cases) and tinea capitis 1, 2
• Examine all family members for onychomycosis and tinea pedis, as household transmission is common and simultaneous treatment of all infected individuals reduces recurrence 3, 2

Identify the Causative Organism

• Trichophyton rubrum is the most common dermatophyte in children (64% of cases), followed by T. tonsurans (18%) and T. mentagrophytes (14%) 1
• Distal and lateral subungual onychomycosis (DLSO) is the most common clinical pattern in children 1

First-Line Treatment: Oral Terbinafine

Weight-Based Dosing Regimen

• < 20 kg: 62.5 mg daily for 12 weeks 3
• 20–40 kg (typical 9-year-old): 125 mg daily for 12 weeks 3
• > 40 kg: 250 mg daily for 12 weeks 3

Why Terbinafine is Preferred

• Superior efficacy: Achieves 46% long-term mycological cure versus 13% with itraconazole in adult studies, with lower relapse rates (23% vs 53%) 3
• Better tolerability: Fewer drug interactions and no risk of hypoglycemia compared to azoles 4
• Children achieve higher cure rates than adults because their nail plates are thinner (allowing better drug penetration) and grow faster (facilitating quicker clearance) 3

Pre-Treatment Safety Requirements

• Obtain baseline liver function tests (ALT, AST) and complete blood count before starting therapy 3, 5
• Terbinafine is not FDA-licensed for pediatric use, making baseline monitoring essential 3
• Contraindications: Renal impairment (creatinine clearance ≤50 mL/min), active or chronic liver disease 5

Common Adverse Effects to Counsel About

• Most common: Headache and gastrointestinal upset (nausea, diarrhea) 3, 5
• Rare but serious: Taste disturbance (potentially permanent), rash, urticaria 3, 5
• Very rare: Hepatotoxicity, Stevens-Johnson syndrome, exacerbation of psoriasis 5

Monitoring During Therapy

• For standard 12-week toenail treatment, routine repeat LFTs are not required unless clinical symptoms develop (e.g., progressive rash, jaundice, abdominal pain) 5
• Discontinue immediately if biochemical liver injury or hepatotoxicity symptoms occur 5

Alternative First-Line Option: Itraconazole Pulse Therapy

When to Use Itraconazole

• If terbinafine is contraindicated (e.g., renal impairment, hepatic disease) or not tolerated 3
• If culture confirms Candida species (itraconazole is more effective than terbinafine for yeast infections) 4

Dosing Regimen

• 5 mg/kg per day for 1 week per month, repeated for 3 pulses (total 3 months) 3
• Administer with food in an acidic gastric environment to optimize absorption 3
• Monitor hepatic function in patients with pre-existing liver abnormalities or when continuous therapy exceeds one month 3

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

Fluconazole

• Dosing: 3–6 mg/kg once weekly for 18–26 weeks 3
• Requires baseline LFTs and CBC 3
• Reserved for cases where both first-line agents are unsuitable 3

Griseofulvin (Not Recommended as First-Line)

• Dosing: 10 mg/kg daily (maximum 500 mg) for prolonged courses 3
• Major limitations: Only 30–40% cure rate, high relapse rate, must be taken with fatty food 3
• Should not be used as first-line therapy due to inferior efficacy 3

Topical Therapy Considerations

Limited Role in Pediatric Toenail Onychomycosis

• Topical agents alone are generally insufficient for toenail disease; systemic therapy remains the preferred approach 3
• No pediatric clinical trials demonstrate efficacy of topical monotherapy for toenail onychomycosis 3

FDA-Approved Topical Options (Adjunctive Use Only)

• Efinaconazole 10% solution: Daily application for 24–48 weeks (approved ≥6 years) 3, 6
• Tavaborole 5% solution: Daily application (approved ≥6 years) 3, 6
• Ciclopirox 8% lacquer: Daily application (approved ≥12 years) 3, 6

Prevention of Recurrence

Footwear and Hygiene Measures

• Apply antifungal powders (miconazole, clotrimazole, or tolnaftate) inside shoes regularly 3, 4
• Decontaminate or replace contaminated footwear 3
• Wear protective footwear (sandals or water shoes) in communal bathing areas, pools, and locker rooms 3, 4
• Keep nails short and clean 3
• Avoid sharing nail clippers with infected family members 3

Treat All Household Members Simultaneously

• Concurrent treatment of all infected family members reduces reinfection risk 3

Follow-Up and Expected Outcomes

Timing of Clinical Assessment

• Re-evaluate at 3–6 months after initiating treatment to assess response 3, 4
• Monitor for at least 48 weeks from treatment start to identify potential relapse 3

Realistic Expectations

• Toenails take approximately 12 months to grow out completely 1
• Complete clinical normalization may not occur even with mycological cure if pre-existing nail dystrophy from trauma or other non-fungal disease is present 4

Critical Pitfalls to Avoid

• Do not treat without mycological confirmation—incorrect diagnosis is the leading cause of treatment failure 1, 4
• Do not use griseofulvin as first-line therapy—it has only 30–40% cure rates and requires prolonged treatment 3
• Do not rely on topical therapy alone for toenail disease—systemic therapy is required for adequate cure rates 3
• Do not forget to examine and treat family members—household transmission perpetuates infection 3, 2