A 32-year-old woman presents with a 6-week history of pruritic, erythematous patches with central clearing on the trunk and proximal limbs. KOH mount shows septate hyphae. What is the drug of choice for tinea corporis?

Explanation

## First-Line Treatment of Tinea Corporis **Key Point:** Terbinafine is the preferred first-line systemic antifungal for dermatophytosis, including tinea corporis, due to superior efficacy and shorter treatment duration. ### Mechanism of Action Terbinafine is an **allylamine** that inhibits squalene epoxidase, blocking ergosterol synthesis in the fungal cell membrane. This results in rapid fungistatic and fungicidal activity against dermatophytes. ### Comparative Efficacy Table | Drug | Class | Mechanism | Duration (Tinea Corporis) | Cure Rate | Advantage | | --- | --- | --- | --- | --- | --- | | **Terbinafine** | Allylamine | Squalene epoxidase inhibitor | 2–4 weeks | 90–95% | Fastest action, shortest course, fungicidal | | Griseofulvin | Polyene | Microtubule disruptor | 4–6 weeks | 85–90% | Older agent, longer duration | | Fluconazole | Azole | Lanosterol 14α-demethylase | 3–4 weeks | 80–85% | Fungistatic, slower onset | | Ketoconazole | Azole | Lanosterol 14α-demethylase | 4–6 weeks | 75–80% | Hepatotoxicity risk, less preferred | ### Clinical Dosing - **Terbinafine:** 250 mg once daily for 2–4 weeks (standard for tinea corporis) - Griseofulvin: 500 mg–1 g daily for 4–6 weeks - Fluconazole: 150 mg weekly for 3–4 weeks **High-Yield:** Terbinafine is **fungicidal** (kills fungi), whereas azoles are **fungistatic** (inhibit growth). This explains faster clinical response and lower relapse rates with terbinafine. **Clinical Pearl:** Topical azoles (miconazole, clotrimazole) are adequate for localized, non-inflammatory tinea corporis; systemic therapy is reserved for extensive, inflammatory, or recurrent disease. **Warning:** Do not confuse terbinafine (allylamine, squalene epoxidase inhibitor) with azoles (cytochrome P450 inhibitors). Terbinafine has fewer drug interactions and is safer in polypharmacy. ### Why Terbinafine is Preferred 1. Shortest treatment duration (2–4 weeks vs. 4–6 weeks for others) 2. Highest cure rate and lowest relapse rate 3. Fungicidal activity (not just fungistatic) 4. Better tissue penetration and accumulation in skin/nails 5. Minimal hepatotoxicity compared to ketoconazole