Uses and safety of acyclovir in pregnancy.

Acyclovir, an antiviral nucleoside analogue, is a widely used agent highly specific for herpes simplex and varicella-zoster viruses. Unintended exposure to acyclovir early in pregnancy, which is not uncommon, may cause excessive maternal and physician anxiety. This drug has not been studied prospectively in large numbers of pregnant women and lacks the Food and Drug Administration's approval for gestational use unless benefits clearly outweigh potential fetal harm. However, data published since acyclovir became available do not indicate increased adverse effects related to its use in pregnancy, especially if prescribed in selected situations, such as disseminated primary herpes simplex infections or maternal varicella pneumonia. This article reports the impact of inadvertent acyclovir exposure on a woman during the first trimester of pregnancy and reviews the literature on acyclovir's pharmacology, safety profile, and potential uses during pregnancy.