Rectal Microbicide Safety and Acceptability Trial of Topically Applied Tenofovir Compared With Oral Tablet

To date, the majority of microbicide research has focused on the assessment of the safety and effectiveness of vaginal microbicides used for the prevention of HIV transmission via the vaginal compartment. Receptive anal intercourse (RAI) is common among men who have sex with men (MSM), and there is increasing evidence that heterosexual women in the developed and developing world also practice anal sex. It can, therefore, be anticipated that once vaginal microbicides are licensed, they will be used in both the vaginal and rectal compartments. As a consequence, there is a need to evaluate both the rectal and vaginal safety profile of candidate microbicides. Therefore, the primary objective of this study is to evaluate the systemic safety of 1% vaginally formulated tenofovir gel applied rectally. In addition, this study will evaluate the immunotoxicity of the gel and evaluate its acceptability; it will also use the oral tenofovir disoproxil fumarate tablets (TDF), rectally-applied tenofovir gel,and a placebo gel to compare their systemic and compartmental pharmacokinetic (pK) profiles. This study was designed to address the following hypotheses: * Vaginally-formulated tenofovir 1% topical gel when applied rectally will be safe using a combination of clinical and laboratory markers including assays specifically designed to measure mucosal toxicity * Tenofovir will be detectable at different concentrations in the various anatomic compartments sampled for pharmacokinetics following single and 7-day topical exposures * Exposure to tenofovir 1% gel will demonstrate prevention of ex vivo HIV-1 challenge using in vivo drug-exposed tissue as compared to baseline tissue samples * Orally delivered, single dose, 300 mg tenofovir disoproxil fumarate tablets will have similar safety profiles using routine blood safety indices as have been established in other trials and will show no mucosal safety concerns * The oral dose will have different multi-compartment concentration kineti