Valacyclovir for herpes simplex virus infection: long-term safety and sustained efficacy after 20 years' experience with acyclovir.

An extensive clinical trial program combined with 5 years' postmarketing experience with valacyclovir provides evidence of favorable safety and efficacy in herpes simplex virus (HSV) management. Valacyclovir enhances acyclovir bioavailability compared with orally administered acyclovir. Long-term use of acyclovir for up to 10 years for HSV suppression is effective and well tolerated. Acyclovir is also approved for use in children, is available in some countries over the counter in cream formulation for herpes labialis, and has been monitored in over 1000 pregnancies. Safety monitoring data from clinical trials of valacyclovir, involving over 3000 immunocompetent and immunocompromised persons receiving long-term therapy for HSV suppression, were analyzed. Safety profiles of valacyclovir (</=1000 mg/day), acyclovir (800 mg/day), and placebo were similar. Extensive sensitivity monitoring of HSV isolates confirmed a very low rate of acyclovir resistance among immunocompetent subjects (<0.5%). The incidence of resistance among immunocompromised patients remains low at about 5%.