Oral Terbinafine for Ringworm (Tinea Corporis/Cruris)
For ringworm of the body or groin (tinea corporis/cruris), oral terbinafine is dosed at 250 mg once daily for 2-4 weeks, with dosing adjusted by body weight in children: 62.5 mg daily for <20 kg, 125 mg daily for 20-40 kg, and 250 mg daily for >40 kg. 1, 2
Critical Treatment Selection Consideration
The causative organism determines treatment success. Terbinafine demonstrates superior efficacy against Trichophyton species (the most common cause of tinea corporis/cruris) but is significantly less effective against Microsporum species, where griseofulvin should be used instead. 1, 3
Standard Adult Dosing
- 250 mg once daily for 2-4 weeks is the recommended regimen for tinea corporis and cruris in adults. 1, 2
- The medication can be taken with or without food, as absorption is not affected by food intake. 3
- Treatment duration of 2 weeks is often sufficient for localized disease, while more extensive infections may require the full 4 weeks. 1
Pediatric Weight-Based Dosing
The British Association of Dermatologists provides clear weight-based dosing for children: 1, 2
- <20 kg: 62.5 mg daily for 2-4 weeks
- 20-40 kg: 125 mg daily for 2-4 weeks
- >40 kg: 250 mg daily for 2-4 weeks
When Oral Therapy is Indicated
Oral terbinafine should be reserved for specific clinical scenarios rather than routine ringworm: 4
- Chronic or extensive disease involving multiple body areas
- Failed topical therapy after adequate trial
- "Moccasin-type" distribution (for tinea pedis)
- Immunocompromised patients requiring systemic treatment
Pre-Treatment Requirements
Obtain baseline liver function tests and complete blood count before initiating therapy, particularly in patients with: 3, 4, 5
- History of heavy alcohol consumption
- Pre-existing liver disease or hepatitis
- Hematological abnormalities
Absolute Contraindications
- Active or chronic liver disease 3, 2, 5
- Lupus erythematosus 3, 2
- History of allergic reaction to oral terbinafine (risk of anaphylaxis) 5
Critical Safety Warnings
The FDA label emphasizes several serious adverse events: 5
- Liver failure (sometimes requiring transplant or resulting in death) - discontinue if liver injury develops
- Taste disturbance (including complete taste loss) - can be severe, prolonged, or permanent
- Smell disturbance (including complete loss of smell) - may be prolonged or permanent
- Stevens-Johnson syndrome and toxic epidermal necrolysis - discontinue immediately if signs of drug reaction occur
- Severe neutropenia - discontinue if neutrophil count ≤1,000 cells/mm³
- Depressive symptoms - monitor for development during treatment
Drug Interactions
Terbinafine has minimal drug-drug interactions compared to azole antifungals, making it safer for patients on multiple medications. 3, 4 The primary concern is with drugs metabolized by cytochrome P450 2D6, including: 3
- Certain antidepressants
- Beta-blockers
- Antiarrhythmic medications
Expected Efficacy
For tinea corporis/cruris caused by dermatophytes, oral terbinafine achieves mycological cure rates of approximately 80-90% when the causative organism is Trichophyton species. 6, 7 However, recent data from India suggests significantly lower cure rates (20-33%) at 4 weeks, possibly reflecting emerging resistance patterns in certain geographic regions. 8
Common Pitfall to Avoid
Do not increase the dose to 500 mg daily expecting better outcomes. A randomized controlled trial demonstrated that 500 mg daily provided no additional benefit over 250 mg daily for tinea corporis/cruris, with similar cure rates (33.3% vs 20%, P=0.82) and no improvement in mycological clearance. 8 The standard 250 mg dose remains appropriate.