A 32-year-old woman presents with severe disseminated varicella-zoster virus (VZV) infection with involvement of multiple dermatomes and signs of meningoencephalitis. She has normal renal function. What is the drug of choice for this condition?

Explanation

## Drug of Choice for Disseminated VZV with CNS Involvement **Key Point:** Acyclovir is the first-line agent for severe, disseminated VZV infection, particularly when CNS involvement (meningoencephalitis) is present, and must be given intravenously in this context. ### Why Acyclovir? 1. **CNS Penetration**: Acyclovir achieves adequate cerebrospinal fluid (CSF) concentrations when given intravenously (10–15 mg/kg IV every 8 hours), making it the gold standard for VZV meningoencephalitis. 2. **Proven Efficacy**: Decades of clinical data support IV acyclovir for severe disseminated VZV with neurological complications. 3. **Renal Function Normal**: The patient has normal renal function, so standard dosing is appropriate without dose adjustment. ### Comparison of Acyclic Nucleosides | Agent | Route | CNS Penetration | Best Use | Limitation | |-------|-------|-----------------|----------|------------| | **Acyclovir** | IV preferred for severe disease | Good (10–15% of serum) | Disseminated VZV, meningoencephalitis, immunocompromised | Requires frequent dosing; poor oral bioavailability | | **Valacyclovir** | Oral (prodrug of acyclovir) | Moderate | Mild–moderate VZV, immunocompetent hosts | Not recommended for CNS disease; oral only | | **Famciclovir** | Oral (prodrug of penciclovir) | Poor | Herpes zoster in immunocompetent; CMV prophylaxis | Inferior CNS penetration; oral only | | **Penciclovir** | Topical (cream) | Negligible | Herpes labialis only | No systemic absorption; topical only | **High-Yield:** For any VZV infection with CNS involvement or severe disseminated disease, **IV acyclovir is mandatory**. Oral agents (valacyclovir, famciclovir) are inadequate for meningoencephalitis. **Clinical Pearl:** Acyclovir nephrotoxicity risk increases with rapid infusion, dehydration, or pre-existing renal impairment. Adequate hydration and slow IV infusion (over 1 hour) minimize this risk. **Mnemonic:** **"ACYCLO for SERIOUS"** — Acyclovir IV for serious/systemic VZV; oral agents for localized, immunocompetent disease.