What is a suitable medication for a 4-year-old with an infected toenail, specifically a fungal (onychomycosis) or bacterial infection?

Treatment of Infected Toenail in a 4-Year-Old

For fungal toenail infection (onychomycosis) in a 4-year-old, oral terbinafine is the first-line treatment at a weight-based dose: 62.5 mg daily if weight <20 kg, or 125 mg daily if weight 20-40 kg, given for 12 weeks for toenails. 1

Confirming the Diagnosis

Before initiating treatment, it is critical to confirm fungal infection through laboratory testing, as other conditions (particularly psoriasis) can mimic onychomycosis in children. 2

• Obtain potassium hydroxide (KOH) preparation and fungal culture to confirm dermatophyte infection before starting systemic therapy 2
• Onychomycosis is less common in young children than adults, making diagnostic confirmation especially important 3
• Check for concomitant tinea pedis and examine family members, as familial disease often occurs 3

First-Line Systemic Treatment

Terbinafine is generally preferred over itraconazole for dermatophyte onychomycosis in children due to its fungicidal activity and efficacy. 1

Terbinafine Dosing (Strength of Recommendation: 1)

• 62.5 mg daily if weight <20 kg 1
• 125 mg daily if weight 20-40 kg 1
• Duration: 12 weeks for toenail infection 1
• Take with food to optimize absorption 1

Important Monitoring Requirements

• Obtain baseline liver function tests and complete blood count before starting treatment 1
• Terbinafine is unlicensed for use in children, making baseline laboratory monitoring particularly important 1
• Contraindicated in hepatic impairment 1

Common Adverse Effects

• Headache, taste disturbance, and gastrointestinal upset 1
• Can aggravate psoriasis and cause subacute lupus-like syndrome 1

Alternative Systemic Options

Itraconazole (Second Choice)

If terbinafine is contraindicated or not tolerated:

• Pulse therapy: 5 mg/kg/day for 1 week per month 1
• Three pulses recommended for toenails (3 months total treatment) 1
• Must be taken with food and acidic pH for optimal absorption 1
• Monitor hepatic function tests in patients with pre-existing abnormalities or when using continuous therapy >1 month 1
• Contraindicated in heart failure and hepatotoxicity 1

Fluconazole (Third-Line)

Consider if both terbinafine and itraconazole are contraindicated or not tolerated:

• 3-6 mg/kg once weekly for 18-26 weeks for toenails 1
• Perform baseline liver function tests and complete blood count 1
• Contraindicated in hepatic and renal impairment 1

Griseofulvin (Last Resort)

Only when newer agents are contraindicated:

• 10 mg/kg/day (maximum 500 mg) for children ≥1 month 1
• Must be taken with fatty food to increase absorption 1
• Lower efficacy and higher relapse rates compared to terbinafine and itraconazole 1

Topical Therapy Considerations

Topical antifungals have limited efficacy as monotherapy but may be considered in specific circumstances:

When Topical Therapy May Be Appropriate

• Superficial or early distal infection with <80% nail plate involvement and no lunula involvement 1
• When systemic therapy is contraindicated 1
• Children may theoretically respond better to topical therapy than adults due to thinner, faster-growing nails 3

Topical Options

• Ciclopirox 8% lacquer: Applied once daily for up to 48 weeks, but only FDA-approved for children >12 years 4, 5
• Efinaconazole 10% solution: FDA-approved for children ≥6 years, with 40% complete cure rate at 52 weeks in pediatric studies 5
• Amorolfine 5% lacquer: Applied once or twice weekly for 6-12 months 1

Important caveat: Topical therapy requires comprehensive nail management including monthly professional removal of infected nail by a healthcare provider trained in nail disorders, plus weekly patient trimming. 4

Critical Management Points

• Treatment duration is prolonged (12 weeks minimum for toenails with systemic therapy), and up to 18 months may be required for complete nail clearance 1
• Recurrence is common in children, possibly more so than adults 3
• Preventive measures are essential: wearing protective footwear in public areas, treating tinea pedis promptly, keeping nails short, and treating all infected family members simultaneously 1
• Complete cure rates are modest: Even with optimal therapy, less than 12% of patients achieve completely clear nails in some studies 4

If Bacterial Infection (Paronychia)

If this is actually a bacterial paronychia rather than fungal onychomycosis:

• Warm water soaks and topical antibiotics for mild cases
• Oral antibiotics (e.g., cephalexin, amoxicillin-clavulanate) for moderate to severe infections
• Incision and drainage if abscess present

The distinction between fungal and bacterial infection is critical, as treatments differ completely. Bacterial paronychia typically presents with acute pain, erythema, and swelling of the nail fold, whereas fungal infection is usually painless with gradual nail plate changes. 1