A 28-year-old man with a 4-week history of tinea pedis (interdigital type) presents with maceration, erosions, and secondary bacterial infection (purulent drainage, mild cellulitis of the foot). He has been using topical terbinafine for 2 weeks without improvement. What is the most appropriate next step in management?

Explanation

## Clinical Scenario Breakdown This patient has **tinea pedis with secondary bacterial superinfection**: - **Primary pathology**: Dermatophyte infection (interdigital tinea pedis) - **Complication**: Maceration → erosions → bacterial colonization (purulent drainage, cellulitis) - **Treatment failure**: Topical terbinafine × 2 weeks without improvement ## Why Oral Terbinafine + Oral Antibiotics Is Correct **Key Point:** When tinea pedis is complicated by secondary bacterial infection and cellulitis, **both the fungal and bacterial infections must be treated simultaneously** with systemic agents. **High-Yield:** Tinea pedis with secondary bacterial infection requires: 1. **Oral antifungal** (terbinafine) — because: - Topical penetration is poor in interdigital spaces (moisture, occlusion) - Systemic therapy achieves higher skin concentrations - Fungicidal action (terbinafine) is faster than topical azoles 2. **Oral antibiotic** (amoxicillin-clavulanate or cephalexin) — because: - Cellulitis is present (spreading erythema, warmth, purulent drainage) - Systemic antibiotic is needed to control bacterial spread - Topical antibiotics alone are insufficient for cellulitis **Clinical Pearl:** The **maceration and erosions in tinea pedis create a portal of entry** for bacteria (usually *Staphylococcus aureus* or *Streptococcus pyogenes*). Treating only the fungus will not resolve the bacterial superinfection; treating only bacteria will allow the fungus to persist and re-seed the infection. ## Dosing for Concurrent Infection | Agent | Dose | Duration | Indication | |-------|------|----------|------------| | **Terbinafine** | 250 mg daily | 2–4 weeks | Dermatophyte | | **Amoxicillin-clavulanate** | 500/125 mg TDS | 7–10 days | β-lactamase-producing bacteria | | Cephalexin | 500 mg QID | 7–10 days | Alternative if penicillin allergy | ## Management Algorithm for Tinea with Superinfection ```mermaid flowchart TD A[Tinea pedis with maceration/erosions]:::outcome --> B{Signs of bacterial infection?}:::decision B -->|No| C[Oral terbinafine 250 mg daily]:::action B -->|Yes: purulent drainage, cellulitis| D[Oral terbinafine + oral antibiotic]:::action C --> E[Review at 2-4 weeks]:::action D --> F[Antibiotic x 7-10 days; antifungal x 2-4 weeks]:::action F --> G[Reassess at 1-2 weeks]:::action G --> H{Cellulitis resolved?}:::decision H -->|Yes| I[Continue antifungal until cure]:::action H -->|No| J[Consider resistant organism or poor compliance]:::urgent ``` **Mnemonic:** **BOTH for BUGS + FUNGI** — When tinea is complicated by bacterial infection, treat **B**oth organisms **O**rally **T**ogether **H**olistically.