Pharmacokinetics of azidothymidine during late pregnancy in Long-Evans rats.

Azidothymidine (Zidovudine) is used to treat symptomatic human immunodeficiency virus infection. It has the ability to reverse seropositivity as well as decrease serum viral titers, and perhaps decrease potential for transmission of the virus. An animal model (pregnant Long-Evans rats) was used to investigate the potential for placental transmission of azidothymidine. The drug crosses the placenta to reach concentrations in the placenta and fetus that are comparable to 75% and 58%, respectively, of those in the maternal serum by 2 hours after administration. By 4 to 6 hours after administration azidothymidine concentrations in the placenta and fetal liver significantly exceed maternal concentrations.