Pharmacology of new antiherpes agents: famciclovir and valacyclovir.

Limitations of acyclovir in treating infections caused by herpes simplex virus include the development of resistant isolates and relatively poor oral bioavailability. Penciclovir and famciclovir may have added clinical utility in the treatment of herpes virus infections in humans. Intracellular pharmacokinetics differ for valacyclovir and famciclovir, but the importance of these differences is unknown. Animal studies suggest that famciclovir (but not valacyclovir) can affect subsequent latent infection with HSV-1; the relevance of these findings to humans requires further investigation. Famciclovir and valacyclovir appear to decrease time to resolution of pain compared with acyclovir in patients with herpes zoster infections.