Valaciclovir – An Improvement Over Aciclovir for the Treatment of Zoster

Abstract

Aciclovir, the first effective antiviral with an acceptable safety profile for the treatment of herpesvirus infections, has shown some limitation in clinical usefulness because of its low oral bioavailability. The search for an improved agent resulted in development of the L-valyl ester of aciclovir, valaciclovir. Valaciclovir has a much improved oral bioavailability and exhibits the same favourable toxicity profile as aciclovir. Following absorption, valaciclovir is rapidly and almost completely converted to aciclovir and the essential amino acid, L-valine. In man, the bioavailability of aciclovir following oral administration of valaciclovir is approximately 54%, compared to only 12-20% for oral aciclovir. A large multicentre study has compared the efficacy and safety of valaciclovir with aciclovir for the treatment of zoster, and has shown significantly improved clinical benefit for valaciclovir. In addition, by retaining the same mode of action and pre-clinical profile as aciclovir, and combined with a similar safety profile in humans, valaciclovir is set to become the new standard in the treatment and prevention of herpesvirus infections and diseases.