High Quality Content by WIKIPEDIA articles! Valaciclovir (INN) or valacyclovir (USAN) is an antiviral drug used in the management of herpes simplex and herpes zoster (shingles). It is a prodrug, being converted in vivo to aciclovir. It is marketed by GlaxoSmithKline under the trade name Valtrex or Zelitrex. As of November 25, 2009 (2009 -11-25), Valacyclovir is being marketed in generic form in the United States by Ranbaxy Laboratories. Valaciclovir is a prodrug, an esterified version of aciclovir that has greater oral bioavailability (about 55%) than aciclovir (10-20%). It is converted by esterases to the active drug aciclovir, as well as the amino acid valine, via hepatic first-pass metabolism.