Although there is a pretty standardized regimen for someone with HSV encephalitis–10 mg/kg per dose every eight hours for 14-21 days– the regimen for HSV meningitis is less clear. Specifically, one question: when can you switch over from IV acyclovir to PO valacyclovir (Valtrex)?
PO valacyclovir, although converted through first-pass metabolism into acyclovir, is less able to penetrate the CNS than IV acyclovir. There are no clear guidelines, but a good rule of thumb is that someone with HSV meningitis should receive at least 7 days of IV acyclovir before being evaluated for a PO regimen of valacyclovir or acyclovir.
NB: HSV PCR is the diagnostic test of choice for HSV encephalitis or meningitis. However it may lose its sensitivity after the first week of infection. PCR > viral culture in terms of sensitivity and specificity.