Case Study: Valacyclovir: A Prodrug of Acyclovir

Abstract

Valacyclovir is an L-valyl ester prodrug of acyclovir that is used for the treatment of herpes, varicella zoster, and cytomegaloviruses. Valacyclovir was developed to increase the oral absorption and plasma levels of acyclovir. Increased plasma concentrations of acyclovir are important in maintaining antiviral activity, especially in immunocompromised patients and in the treatment of less sensitive viruses such as VZV and CMV (Beauchamp et al., 1992). Suboptimal exposures can lead to more resistant viral strains. To achieve high enough exposures, acyclovir must be dosed intravenously or in multiple high doses (de Miranda and Burnette, 1994). In the design of valacyclovir, the following criteria were met: it was as safe as acyclovir, efficiently converted, and gave exposures after oral administration that were comparable to plasma levels of intravenously dosed acyclovir. Several reviews describe the development, pharmacokinetics, and efficacy of valacyclovir (Crooks and Murray 1994; Beutner, 1995; Perry and Faulds, 1996).