A pharmacology study showed very low concentrations of tenofovir appearing in the women's blood, while high levels of tenofovir in cervicovaginal fluid linked with better HIV protection.
“I was struck by the lack of any degree of [HIV] resistance from the topical application of this drug,” said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. He speculated that tenofovir penetrates the mucosal surface of the vagina and enters submucosal dendritic and T cells where it blocks HIV replication and thus prevents infection from starting.