A 52-year-old sugarcane farmer from rural Maharashtra presents with a 2-week history of progressive corneal opacity, pain, and blurred vision in the left eye. He sustained a corneal abrasion from a plant thorn 3 weeks ago. Slit-lamp examination shows a grayish-white stromal infiltrate with feathery borders and minimal anterior chamber reaction. KOH mount of corneal scrapings reveals branching septate hyphae. What is the drug of choice for topical antifungal therapy?

Explanation

## Fungal Corneal Ulcer — First-Line Antifungal Therapy **Key Point:** Natamycin 5% is the **gold-standard topical antifungal** for fungal keratitis, particularly for filamentous fungi (Aspergillus, Fusarium) and Candida species. ### Why Natamycin 5% Is First-Line 1. **Broad antifungal spectrum**: Effective against most clinically relevant fungi — Candida, Aspergillus, Fusarium, Cephalosporium. 2. **Excellent corneal penetration**: Polyene macrolide with superior corneal epithelial and stromal penetration compared to azoles. 3. **Fungistatic + fungicidal**: Binds to fungal cell membrane ergosterol, disrupting membrane integrity. 4. **Minimal systemic absorption**: Topical application achieves high local concentration with negligible systemic toxicity. 5. **Proven efficacy**: Multiple randomized trials (including the Mycotic Ulcer Treatment Trial — MUTT) demonstrate superior healing rates with natamycin vs. voriconazole for filamentous fungi. ### Dosing and Administration - **Frequency**: Every 1–2 hours while awake (initially), then taper as ulcer improves. - **Duration**: 4–6 weeks or until complete epithelialization and stromal clearing. - **Adjunct**: Systemic antifungal (oral itraconazole or voriconazole) for deep stromal or scleral involvement. **High-Yield:** Natamycin is **insoluble in water** — it is supplied as a **suspension**, not a solution. Shake the bottle before each use to ensure uniform concentration. ### Comparison of Topical Antifungal Agents | Agent | Class | Spectrum | Corneal Penetration | Indication | Advantage | Limitation | |-------|-------|----------|-------------------|-----------|-----------|------------| | Natamycin 5% | Polyene | Filamentous fungi, Candida | Excellent | **Empirical fungal ulcer** | Best overall efficacy | Suspension (shake before use); less effective for Candida alone | | Amphotericin B 0.15% | Polyene | Broad (fungi + some Candida) | Moderate–good | Candida, severe infections | Fungicidal | Corneal toxicity at higher concentrations; less available | | Voriconazole 1% | Azole | Filamentous fungi, Candida | Good | Candida-predominant, azole-resistant | Good for Candida | Inferior to natamycin for Aspergillus/Fusarium (MUTT trial); slower healing | | Fluconazole 0.2% | Azole | Candida > filamentous | Poor | Candida keratitis | Oral formulation available | Weak corneal penetration; not recommended for filamentous fungi | **Clinical Pearl:** The **feathery borders** and **branching septate hyphae** in this case are classic for **Aspergillus** (a filamentous fungus) — natamycin is the proven first-line choice. Aspergillus is the most common cause of fungal keratitis in tropical/subtropical regions (India, Africa) due to agricultural trauma. **Warning:** Do not use **systemic azoles alone** (fluconazole, itraconazole) as monotherapy for fungal keratitis — corneal penetration is insufficient. Always combine with topical natamycin or amphotericin B. **Mnemonic:** **NAFVAC** — **N**atamycin (first-line), **A**mphotericin B, **F**ilamentous fungi, **V**oriconazole, **A**zoles, **C**andida. - For filamentous fungi (Aspergillus, Fusarium) → **Natamycin** first. - For Candida alone → Natamycin or Amphotericin B. - Azoles (voriconazole, fluconazole) → second-line or adjunct only.