What is the recommended initial antiviral therapy for suspected herpes simplex virus encephalitis?

• A. Ganciclovir
• B. Foscarnet
• C. Valacyclovir
• D. Acyclovir 10 mg/kg IV every 8 hours (renal dose adjustment)

Answer: (D)

When HSV encephalitis is suspected, treat immediately with IV acyclovir. This condition progresses rapidly and delays in therapy markedly increase mortality, so empirical treatment is started before confirmatory tests return. Acyclovir targets HSV by inhibiting viral DNA polymerase after activation by viral thymidine kinase, and it achieves effective concentrations in the CNS, which is crucial for encephalitis.

The standard initial dosing is 10 mg/kg IV every 8 hours, with adjustments based on renal function to prevent accumulation and toxicity, since acyclovir is primarily cleared by the kidneys. Start this regimen promptly and continue while CSF PCR results are pending.

Other antivirals like ganciclovir or foscarnet are not first-line for HSV encephalitis and are generally reserved for specific scenarios (such as CMV disease or acyclovir-resistant HSV). Valacyclovir is oral and does not provide reliable CNS drug levels quickly enough to treat encephalitis, so it’s not appropriate as initial therapy.