## Viral Keratitis and Antiviral Therapy ### Clinical Presentation The dendritic ulcer with terminal bulbs is pathognomonic for **herpes simplex virus (HSV) keratitis**, the most common cause of infectious corneal blindness in developed countries. **Key Point:** The dendritic ulcer is a branching epithelial defect with swollen terminal bulbs at the ends—a hallmark finding of HSV-1 keratitis. ### Drug of Choice: Acyclovir **High-Yield:** Acyclovir is the first-line antiviral agent for HSV keratitis and is available in multiple formulations: | Formulation | Dosing | Indication | |---|---|---| | **Topical ointment** | 5% acyclovir, 5 times daily | Epithelial keratitis (first-line) | | **Oral** | 400–800 mg, 4–5 times daily | Systemic therapy; adjunct to topical | | **IV** | 10–15 mg/kg/8 hr | Severe disease, immunocompromised | ### Mechanism of Action 1. Acyclovir is a nucleoside analogue that requires viral thymidine kinase (TK) for activation. 2. Once phosphorylated, it inhibits viral DNA polymerase and causes chain termination. 3. High selectivity for HSV-infected cells due to viral TK specificity. **Clinical Pearl:** Topical acyclovir ointment is preferred over drops because the ointment formulation maintains longer corneal contact time and better penetration into the epithelium. ### Treatment Duration & Outcomes - **Epithelial keratitis:** Typically resolves in 7–10 days with topical acyclovir. - **Stromal keratitis:** May require systemic acyclovir plus topical corticosteroids (after epithelial healing) to reduce inflammation. - **Recurrent HSV keratitis:** Prophylactic oral acyclovir (400 mg twice daily) reduces recurrence risk by ~50%. **Warning:** Topical corticosteroids should NOT be used during active epithelial disease as they promote viral replication and geographic ulceration. They are reserved for stromal disease after epithelial healing is confirmed.
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