A 28-year-old female gym instructor from Delhi presents with a 6-week history of scaly patches on her feet, particularly between the toes and on the soles. She reports intense itching, especially in the evening. On examination, she has maceration and fissuring between the fourth and fifth toes, with a well-demarcated erythematous plaque extending to the sole. Wood's lamp examination is negative. KOH mount shows branching septate hyphae. She has tried topical azoles without improvement. What is the next best management step?

Explanation

## Clinical Diagnosis: Tinea Pedis — Treatment Failure ### Case Analysis **Key Point:** This patient has tinea pedis (athlete's foot) with features of the interdigital type (maceration, fissuring between toes) progressing to the plantar surface. The 6-week duration with failure of topical azole therapy suggests either inadequate penetration, poor compliance, or a dermatophyte species with reduced azole susceptibility. **Key Point:** Negative Wood's lamp rules out *Malassezia* (tinea versicolor) and confirms dermatophyte infection (septate hyphae on KOH). ### Treatment Algorithm for Tinea Pedis ```mermaid flowchart TD A[Tinea Pedis confirmed by KOH]:::outcome --> B{Extent & severity?}:::decision B -->|Localized, mild| C[Topical azole or terbinafine]:::action B -->|Extensive or failed topical| D[Systemic antifungal]:::action C --> E{Response at 4 weeks?}:::decision E -->|Yes| F[Continue topical to 4-6 weeks total]:::action E -->|No| G[Switch to systemic therapy]:::action D --> H[Terbinafine 250 mg daily × 4-6 weeks]:::action G --> H H --> I[Clinical cure in 80-90% of cases]:::outcome ``` ### Why Systemic Therapy is Indicated | Criterion | This Patient | Status | |-----------|--------------|--------| | **Duration** | 6 weeks | Prolonged | | **Topical trial** | Azole × 6 weeks | Failed | | **Extent** | Interdigital + plantar | Moderate-to-extensive | | **Symptoms** | Severe itching, maceration | Active inflammation | | **Indication for systemic** | Yes | **Meets criteria** | **High-Yield:** Systemic antifungal therapy is indicated when: 1. Topical therapy has failed after adequate trial (≥4 weeks) 2. Lesions are extensive or involve the plantar surface 3. Patient has onychomycosis (nails involved) 4. Immunocompromised state ### Terbinafine vs. Azoles for Systemic Use | Feature | Terbinafine | Itraconazole | Fluconazole | |---------|-------------|--------------|-------------| | **MOA** | Allylamine (fungicidal) | Azole (fungistatic) | Azole (fungistatic) | | **Efficacy in tinea pedis** | 80–90% | 70–80% | 60–70% | | **Duration** | 4–6 weeks | 4 weeks or pulsed | 6–12 weeks | | **Hepatotoxicity** | Rare | Moderate risk | Low | | **Drug interactions** | Moderate | High | Moderate | | **Cost** | Moderate | Higher | Lower | | **DOC for tinea pedis** | **Yes** | Alternative | Alternative | **Clinical Pearl:** Terbinafine is superior for dermatophyte infections because it is fungicidal (kills the organism) rather than fungistatic (inhibits growth). It achieves high concentrations in keratin and has a post-antifungal effect, allowing shorter treatment duration. ### Why Other Options Are Incorrect **Option A (Continue topical azoles):** The patient has already failed 6 weeks of topical azole therapy. Continuing the same failed regimen violates the principle of treatment escalation and wastes time. **Option C (Topical tolnaftate):** Tolnaftate is a thiocarbamate with lower efficacy than azoles or terbinafine. Switching to a weaker topical agent after azole failure is illogical and unlikely to succeed. **Option D (Await culture):** While fungal culture can identify the organism and guide therapy, it is not the next best step in acute management. Culture takes 2–4 weeks and is reserved for atypical presentations, recurrent infections, or suspected non-dermatophyte molds. Empiric systemic therapy should begin immediately given the clear clinical diagnosis and treatment failure. ### Management Protocol 1. **Systemic terbinafine 250 mg once daily for 4–6 weeks** 2. **Concurrent topical antifungal** (optional, to reduce spore shedding) 3. **Hygiene measures:** Keep feet dry, wear breathable footwear, avoid shared showers 4. **Follow-up:** Clinical assessment at 4 weeks; if inadequate response, consider culture or alternative diagnosis (e.g., non-dermatophyte mold, bacterial superinfection) **Mnemonic:** **TERBINAFINE** = **T**opical failed → **E**scalate to **R**ecognized **B**est **I**nternal **N**on-**A**zole **F**ungicide **I**n **N**ail and **E**xtensive disease. [cite:Harrison 21e Ch 212; KD Tripathi 8e Ch 77]