Valacyclovir: a review of its antiviral activity, pharmacokinetic properties, and clinical efficacy.

Oral administration of the prodrug valacyclovir results in enhanced bioavailability and significantly greater plasma concentrations of acyclovir than can be achieved with oral doses of acyclovir itself. The results of clinical trials with valacyclovir have demonstrated significant benefits in the resolution of pain associated with herpes zoster infection. Efficacy parameters were similar for valacyclovir and acyclovir in the treatment of herpes simplex; however the results were achieved with lower and less-frequent doses of valacyclovir. The cost of a course of therapy with valacyclovir is expected to be similar to that of other antivirals. The potential clinical benefits of valacyclovir will likely be apparent in the case of acyclovir-resistant herpesvirus infections, where high-dose intravenous treatment with acyclovir has been necessary. Most of these resistant viruses have been encountered in immunocompromised patients, and the resistance has been attributed to inadequate exposure to the drug. Because optimal levels of acyclovir are achieved with a simpler dosing regimen of valacyclovir, compliance may be improved in many patients, thus reducing the incidence of resistant virus.