A 32-year-old male farmer from rural Maharashtra presents with severe itching and maceration between the 4th and 5th toes for 3 weeks. On examination, there is erythema, scaling, and fissuring in the interdigital web space. KOH mount confirms fungal elements. He has tried topical antifungals for 1 week without improvement. What is the most appropriate next step in management?

Explanation

## Clinical Scenario Analysis This patient presents with **tinea pedis** (athlete's foot) affecting the interdigital space — the most common site of dermatophyte infection in the foot. The key clinical clues are: - Interdigital location (4th–5th toe web) - Erythema, scaling, and maceration - KOH mount positive (confirmed fungal infection) - **Failure to respond to topical therapy after 1 week** ## Why Oral Terbinafine Is Indicated **Key Point:** Tinea pedis with interdigital involvement and maceration indicates a **moist, intertriginous environment** that favors deeper dermatophyte penetration and poor topical drug penetration. Once-daily topical therapy is often insufficient. **High-Yield:** The presence of maceration (tissue breakdown) and failure of topical therapy within 1 week is the trigger for **systemic antifungal therapy**. **Clinical Pearl:** Terbinafine is preferred over fluconazole for tinea pedis because it achieves superior nail and stratum corneum concentrations and has faster clinical and mycological cure rates [cite:Inamadar & Palit, Dermatology Essentials]. ## Dosing & Duration | Agent | Dose | Duration | Notes | |-------|------|----------|-------| | **Terbinafine** | 250 mg once daily | 2–4 weeks | First-line for tinea pedis; fungicidal | | Fluconazole | 150 mg once weekly | 2–4 weeks | Fungistatic; slower response | | Itraconazole | 100–200 mg daily | 2–4 weeks | Alternative; less preferred | **Key Point:** Oral terbinafine 250 mg daily for 2–4 weeks is the **gold standard** for interdigital tinea pedis with maceration and topical treatment failure. ## Management Algorithm ```mermaid flowchart TD A["Tinea pedis confirmed by KOH"]:::outcome --> B{"Interdigital with maceration?"}:::decision B -->|Yes| C{"Topical therapy response?"}:::decision C -->|Good response| D["Continue topical + reassess at 4 weeks"]:::action C -->|No response after 1 week| E["Start oral terbinafine 250 mg daily"]:::action E --> F["Duration: 2–4 weeks"]:::action F --> G["Review at 4 weeks"]:::outcome ``` ## Adjunctive Measures - Keep feet dry; use antifungal powder between toes - Avoid occlusive footwear - Change socks if damp - Topical therapy can continue alongside oral agent for symptom relief