A 32-year-old woman presents with a 5-day history of unilateral eye pain, photophobia, and blurred vision. Slit-lamp examination reveals a dendritic ulcer with terminal bulbs on the cornea, and Giemsa staining shows multinucleated giant cells. What is the drug of choice for this condition?

Question

Accepted Answer

B. Acyclovir. ## Diagnosis: Herpes Simplex Virus (HSV) Keratitis

**Key Point:** The dendritic ulcer with terminal bulbs and multinucleated giant cells on Giemsa staining are pathognomonic for HSV keratitis.

## Drug of Choice: Acyclovir

### Mechanism
- Nucleoside analogue that inhibits viral DNA polymerase
- Requires viral thymidine kinase for activation (high selectivity for infected cells)
- Prevents viral DNA chain elongation

### Dosing & Route
- **Topical:** Acyclovir 3% ointment, 5 times daily for 7–10 days
- **Systemic:** 400–800 mg orally 5 times daily for 10–14 days (for severe or disseminated disease)
- Topical therapy is usually sufficient for uncomplicated epithelial keratitis

**High-Yield:** Acyclovir is the first-line agent for HSV keratitis because it is effective, well-tolerated, and has the longest safety record in ophthalmology.

## Comparison with Other Antivirals

| Agent | Mechanism | Use in HSV Keratitis | Limitation |
|-------|-----------|----------------------|------------|
| Acyclovir | HSV DNA polymerase inhibitor | First-line, topical & systemic | Requires viral TK; resistance rare |
| Ganciclovir | CMV DNA polymerase inhibitor | CMV retinitis (immunocompromised) | Not preferred for HSV; more toxic |
| Cidofovir | Nucleotide analogue | CMV retinitis | Nephrotoxic; not for HSV |
| Foscarnet | Pyrophosphate analogue | Acyclovir-resistant HSV (rare) | Nephrotoxic; second-line only |

**Clinical Pearl:** Acyclovir-resistant HSV is extremely rare in immunocompetent patients but may occur in severely immunocompromised individuals (e.g., advanced HIV). In such cases, foscarnet or cidofovir may be considered.

## Adjunctive Management
- Topical cycloplegic agents (cyclopentolate 1%) to relieve pain and prevent posterior synechiae
- Avoid topical corticosteroids in epithelial keratitis (risk of geographic ulcer)
- Systemic NSAIDs for pain control
- Lubricating drops for comfort

**Warning:** Do not use topical corticosteroids alone in HSV keratitis—they can worsen the infection and cause a "herpetic geographic ulcer." Steroids may be used ONLY with concurrent antiviral therapy and under close ophthalmologic supervision.

Answer

A. Foscarnet

Answer

C. Ganciclovir

Answer

D. Cidofovir

A 32-year-old woman presents with a 5-day history of unilateral eye pain, photophobia, and blurred vision. Slit-lamp examination reveals a dendritic ulcer with terminal bulbs on the cornea, and Giemsa staining shows multinucleated giant cells. What is the drug of choice for this condition?

Explanation

Diagnosis: Herpes Simplex Virus (HSV) Keratitis

Drug of Choice: Acyclovir

Mechanism

Dosing & Route

Comparison with Other Antivirals

Adjunctive Management

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Agent	Mechanism	Use in HSV Keratitis	Limitation
Acyclovir	HSV DNA polymerase inhibitor	First-line, topical & systemic	Requires viral TK; resistance rare
Ganciclovir	CMV DNA polymerase inhibitor	CMV retinitis (immunocompromised)	Not preferred for HSV; more toxic
Cidofovir	Nucleotide analogue	CMV retinitis	Nephrotoxic; not for HSV
Foscarnet	Pyrophosphate analogue	Acyclovir-resistant HSV (rare)	Nephrotoxic; second-line only