A 32-year-old woman presents with a 6-week history of pruritic, scaly patches on both groins and inner thighs. Examination reveals well-demarcated erythematous plaques with a raised, advancing border and central clearing. KOH mount of scale shows branching septate hyphae. She has already used topical antifungals (clotrimazole) for 3 weeks without improvement. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient has **tinea cruris** (jock itch) confirmed by: - Clinical morphology: well-demarcated erythematous plaques with raised border and central clearing - KOH positivity: branching septate hyphae (dermatophyte) - **Failure of topical therapy after 3 weeks** — the key trigger for systemic treatment ## Why Oral Terbinafine Is the Next Step **Key Point:** Tinea of intertriginous areas (groin, axillae, inframammary folds) that fails topical therapy for ≥2–3 weeks requires **systemic antifungal therapy**. **High-Yield:** Terbinafine is the **first-line oral agent** for dermatophyte infections because: 1. **Fungicidal** (not fungistatic) — kills the organism 2. **Shorter duration**: 2–4 weeks for tinea corporis/cruris (vs. 4–6 weeks for azoles) 3. **Better efficacy** in warm, moist areas where topical penetration is poor 4. **Oral bioavailability** is excellent; achieves high concentrations in skin and nails **Clinical Pearl:** Intertriginous tinea is notoriously prone to treatment failure with topicals alone because: - Moisture and maceration impair drug penetration - Occlusion favours fungal growth - Compliance is often suboptimal in skinfolds ## Dosing & Duration | Agent | Dose | Duration (Tinea Cruris) | Notes | |-------|------|------------------------|-------| | **Terbinafine** | 250 mg daily | 2–4 weeks | Fungicidal; first-line | | Fluconazole | 150 mg weekly | 4–6 weeks | Fungistatic; slower | | Itraconazole | 200 mg daily | 4 weeks | Fungistatic; less preferred | ## Management Algorithm ```mermaid flowchart TD A[Tinea cruris diagnosed by KOH]:::outcome --> B[Topical azole/allylamine x 2-3 weeks]:::action B --> C{Clinical improvement?}:::decision C -->|Yes| D[Continue topical until clear]:::action C -->|No| E[Start oral terbinafine 250 mg daily]:::action E --> F[Review at 2-4 weeks]:::action F --> G{Healed?}:::outcome G -->|Yes| H[Counselling: moisture control, antifungal powder]:::action G -->|No| I[Reassess diagnosis; consider resistant organism]:::urgent ``` **Mnemonic:** **TERBINAFINE for TINEA** — **T**erbinafine is **T**he **T**op choice for **T**opical-**R**esistant dermatophyte infections.