How do I apply terbinafine (antifungal medication)?

How to Apply Terbinafine

Oral Administration (Systemic Treatment)

Terbinafine is taken orally as a tablet, not applied topically for most fungal infections requiring systemic therapy. 1

Dosing Regimens

For onychomycosis (nail fungal infections):

• Fingernail infections: 250 mg once daily for 6 weeks 2, 1
• Toenail infections: 250 mg once daily for 12 weeks (some guidelines extend to 16 weeks) 2, 1
• Can be taken with or without food 1
• Take at the same time each day for consistency 1

For cutaneous dermatophyte infections (tinea corporis/cruris, tinea pedis):

• 250 mg once daily for 2-4 weeks 3, 4

Pediatric dosing (for tinea capitis and other dermatophyte infections):

• Children <20 kg: 62.5 mg once daily 3
• Children 20-40 kg: 125 mg once daily 3
• Children >40 kg: 250 mg once daily 5
• Treatment duration typically 2-4 weeks 3, 5

Important Administration Instructions

• If you miss a dose: Take it as soon as you remember, unless it is less than 4 hours before the next scheduled dose—in that case, skip the missed dose and resume your regular schedule 1
• Do not double doses 1
• Tablets should be swallowed whole 1

Topical Administration (For Limited Cutaneous Infections)

Topical terbinafine 1% cream is applied directly to affected skin areas:

• Apply once or twice daily to clean, dry skin 6, 4
• Continue for 1-2 weeks for most cutaneous infections 4
• Ensure complete drying of affected areas (especially skin folds) after bathing to prevent recurrence 3

When Topical vs. Oral Treatment is Appropriate

Topical treatment is suitable for:

• Limited cutaneous infections without hair follicle involvement 3
• Tinea corporis/cruris, tinea pedis, cutaneous candidiasis, pityriasis versicolor 6, 4

Oral treatment is required for:

• Onychomycosis (nail infections) 2
• Tinea capitis (scalp ringworm)—topical therapy alone is not recommended 7
• Extensive or severe infections 7
• Infections involving hair follicles 3

Critical Safety Monitoring

Before starting treatment:

• Obtain baseline liver function tests (ALT and AST) 1
• Confirm fungal infection with microscopy and culture 2
• Complete blood count if history of hematological abnormalities 2

During treatment, watch for warning signs requiring immediate discontinuation:

• Liver problems: Nausea, vomiting, abdominal pain, jaundice, dark urine, pale stools, unusual fatigue 1
• Taste or smell disturbance: May be prolonged or permanent 1
• Severe skin reactions: Rash, blisters, peeling skin, mouth sores 1
• Depressive symptoms: Mood changes, loss of interest, sleep disturbances 1

Common Pitfalls to Avoid

• Do not use oral terbinafine for Candida infections—it has only fungistatic activity against yeasts and is inferior to azoles for these infections 2, 8
• Do not use in pregnancy—terbinafine is FDA pregnancy category B but should be avoided; wait until after delivery for non-urgent infections 2, 1
• Avoid in patients with active or chronic liver disease 2, 1
• Monitor for drug interactions with CYP2D6 substrates (antidepressants, beta-blockers), rifampin, cimetidine, cyclosporine 1
• Re-evaluate at 3-6 months after starting treatment for nail infections—mycological cure may take longer than clinical improvement 2

Expected Outcomes

• Mycological cure rates: 70-80% for toenail onychomycosis, 80-90% for fingernail infections 2, 8
• Drug persists in nails for at least 30 weeks after treatment completion, allowing continued antifungal effect 2, 8
• Improvement continues after stopping treatment due to residual drug levels and fungicidal mechanism 4