Oral Terbinafine for Ringworm: Dosing Recommendations
For cutaneous ringworm (tinea corporis/cruris), oral terbinafine 250 mg once daily for 2-4 weeks is the recommended treatment when systemic therapy is indicated, though topical therapy is typically first-line for limited disease. 1
When to Use Oral vs. Topical Therapy
- Topical therapy is appropriate for limited disease without hair follicle involvement 1
- Oral therapy is indicated for extensive infections, those involving hair follicles, or infections not responding to topical treatment within 2 weeks 2
- For tinea capitis (scalp ringworm), topical therapy alone is not recommended and oral therapy is generally indicated 2
Standard Dosing for Cutaneous Ringworm (Tinea Corporis/Cruris)
Adults
- 250 mg once daily for 2-4 weeks 1, 3
- Higher doses (500 mg daily) have not shown additional benefit over 250 mg in recent comparative studies 4
Pediatric Dosing (Weight-Based)
- Children <20 kg: 62.5 mg once daily for 2-4 weeks 1
- Children 20-40 kg: 125 mg once daily for 2-4 weeks 1
- Children >40 kg: 250 mg once daily for 2-4 weeks 1
Important Distinction: Onychomycosis Dosing (Not Ringworm)
The FDA-approved dosing for nail infections differs significantly and should not be confused with cutaneous ringworm treatment:
- Fingernail onychomycosis: 250 mg daily for 6 weeks 5
- Toenail onychomycosis: 250 mg daily for 12 weeks 6, 5
Clinical Efficacy Considerations
- Mycological cure rates exceed 80% for cutaneous dermatophyte infections with appropriate dosing 3, 7
- Short treatment duration (2-4 weeks) improves patient compliance compared to longer regimens 1
- The endpoint of treatment should be mycological rather than just clinical cure 1
- Treatment failure may be due to poor compliance, suboptimal drug absorption, or organism insensitivity 1
Safety Monitoring and Contraindications
Baseline Monitoring
- Obtain pretreatment serum transaminases (liver function tests) 5
- Baseline monitoring is particularly important in patients with history of heavy alcohol consumption, hepatitis, or haematological abnormalities 6
- Complete full blood count is recommended in patients with pre-existing risk factors 6
Absolute Contraindications
- History of allergic reaction to oral terbinafine (risk of anaphylaxis) 5
- Active or chronic liver disease 6
- Lupus erythematosus 1
- Porphyria 1
Common Side Effects (Warn Patients)
- Gastrointestinal disturbances (49%): nausea, diarrhea, dyspepsia, abdominal pain 6, 5
- Dermatological reactions (23%): rash, pruritus, urticaria 6, 5
- Taste disturbance can be severe, prolonged, or permanent—discontinue if this occurs 6, 5
- Smell disturbance may be prolonged or permanent—discontinue if this occurs 5
Serious Adverse Events (Rare but Important)
- Liver failure requiring transplant or causing death has occurred—discontinue if liver injury develops 5
- Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported 6, 5
- Severe neutropenia—discontinue if neutrophil count ≤1,000 cells/mm³ 5
- Depressive symptoms have been reported—monitor for development 5
- Incidence of serious adverse events is approximately 0.04% 6
Drug Interactions
- Terbinafine has minimal drug-drug interactions compared to azole antifungals 6
- The only potentially significant interaction is with drugs metabolized by cytochrome P450 2D6 isoenzyme 6
- Specific interactions noted with desipramine, cimetidine, fluconazole, cyclosporine, rifampin, and caffeine 5
Adjunctive Measures
- Complete drying of affected areas after bathing helps prevent recurrence 1
- Topical clotrimazole may be used concurrently with oral therapy 4
Special Populations
Tinea Capitis (Microsporum canis)
- Doubled doses may be required for M. canis infections: 10-25 kg receive 125 mg/day; >25 kg receive 250 mg/day 8
- Standard doses are often inadequate for this organism 8