Standard dosage	10 mg/kg IV (over 1 h) given every 8 h; maximum of 20 mg/kg every 8 h. Duration of treatment in the original randomized trials of acyclovir for HSV encephalitis was 10 days. However, clinical relapse after 10 days treatment is known to occur [27, Class IV]. As a consequence, most clinicians now use at least 14 to 21 days intravenous treatment in confirmed cases. Some advocate repeating a CSF examination at 14 to 21 days, and continuing treatment until the CSF is negative of virus by PCR [27, Class IV]. A prolonged duration of therapy may be more important in the immunosuppressed patients.
Contraindications	Hypersensitivity to acyclovir or valacyclovir.
Main drug interactions	Due to induction of liver enzymes, drugs processed through the liver such as valproate and phenytoin may decrease in concentration. Due to effects on the kidney, drugs excreted through the kidney may increase in concentration with concomitant use with acyclovir.
Major side effects	Nephrotoxicity, thrombotic thrombocytopenic purpura, Stevens Johnson syndrome (rare).
Special points	Oral valacyclovir has been used in pediatric practice, especially when maintaining intravenous access has proved difficult; in adults it may have a role in ongoing treatment, particularly in patients with HSV detectable in the CSF after 2 to 3 weeks. The NIAID Collaborative Antiviral Study Group is assessing the role of high-dose valacyclovir (2 g three times daily) for 3 months [28].