A 32-year-old man presents with pruritic, scaly patches on the groin and inner thighs for 3 weeks. KOH mount confirms branching septate hyphae. What is the drug of choice for tinea cruris?

Explanation

## First-Line Treatment of Tinea Cruris **Key Point:** Terbinafine is the gold-standard first-line agent for dermatophyte infections, including tinea cruris, due to superior efficacy, shorter duration, and better tissue penetration. ### Mechanism & Pharmacokinetics Terbinafine is an **allylamine antifungal** that inhibits squalene epoxidase, blocking ergosterol synthesis. It achieves high concentrations in skin, nails, and hair, making it ideal for dermatophytosis. ### Dosing & Duration | Parameter | Terbinafine | Griseofulvin | Fluconazole | |-----------|-------------|--------------|-------------| | **Dose** | 250 mg once daily | 500 mg–1 g daily (divided) | 150–200 mg weekly | | **Duration (tinea cruris)** | 2–4 weeks | 4–6 weeks | 3–4 weeks | | **Fungistatic/Cidal** | Fungicidal | Fungistatic | Fungistatic | | **Tissue penetration** | Excellent (skin, nails) | Moderate | Moderate | **High-Yield:** Terbinafine achieves cure in 2–4 weeks for tinea cruris; griseofulvin requires 4–6 weeks and is now second-line. ### Clinical Advantages of Terbinafine 1. **Faster cure**: Fungicidal action (kills organisms) vs. fungistatic (inhibits growth) 2. **Shorter treatment**: 2–4 weeks vs. 4–6 weeks with griseofulvin 3. **Better CNS penetration**: Useful for severe/disseminated disease 4. **Oral bioavailability**: Not food-dependent (griseofulvin requires fatty meals) 5. **Single daily dose**: Improves compliance **Clinical Pearl:** Tinea cruris, tinea corporis, and tinea pedis are all best treated with oral terbinafine 250 mg daily for 2–4 weeks. Topical azoles (miconazole, clotrimazole) are reserved for mild, localized disease. ### Why Terbinafine Over Alternatives ```mermaid flowchart TD A[Dermatophyte infection diagnosed]:::outcome --> B{Extent & severity?}:::decision B -->|Localized, mild| C[Topical azole or terbinafine]:::action B -->|Extensive or nail involvement| D[Oral antifungal needed]:::action D --> E{First-line oral agent?}:::decision E -->|Terbinafine preferred| F[250 mg once daily, 2-4 weeks]:::action E -->|Allergy or contraindication| G[Griseofulvin or fluconazole]:::action F --> H[Cure in 2-4 weeks]:::outcome G --> I[Cure in 4-6 weeks]:::outcome ``` **Mnemonic:** **TALL** = **T**erbinafine is **A**llylamine, **L**ong-acting, **L**ow relapse — remember terbinafine as the tall choice (first-line, superior height of efficacy). **Warning:** Griseofulvin is now relegated to second-line due to longer treatment duration and lower cure rates. Do not confuse it with terbinafine in modern NEET PG exams.