For HSV encephalitis, what is the recommended acyclovir dosing and route?

• A. IV acyclovir, 5 mg/kg every 12 hours for adults
• B. IV acyclovir, 10 mg/kg every 8 hours for adults, adjust for renal function
• C. Oral acyclovir, 400 mg every 6 hours
• D. IV acyclovir, 20 mg/kg every 24 hours

Answer: (B)

HSV encephalitis demands rapid and reliable CNS drug exposure, which is best achieved with intravenous therapy rather than oral. Acyclovir given IV achieves therapeutic levels in the CSF quickly, helping to halt viral replication in the brain where the infection is most dangerous. The standard adult regimen uses a dose of 10 mg/kg every 8 hours, and this dosing is adjusted based on renal function because acyclovir is cleared by the kidneys. If kidney function is reduced, the interval between doses or the dose itself is lowered to prevent accumulation and toxicity while still maintaining antiviral activity.

Why the other approaches aren’t ideal: oral acyclovir has poor and inconsistent CSF penetration, so it would not provide reliable CNS levels needed for encephalitis. A lower dose given less frequently (for example, 5 mg/kg every 12 hours) would likely fail to achieve the necessary CNS concentrations. A much larger dose given once every 24 hours does not maintain steady-state levels and risks toxicity or subtherapeutic exposure.