The study will be a randomized, open-label, cross-over clinical pharmacokinetic trial to investigate a strategy for probenecid "boosting" in the setting of tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC) for HIV pre-exposure prophylaxis (PrEP). The study will be conducted at the Indiana University Clinical Research Center. All samples will be processed and the amount of tenofovir/FTC in plasma, blood, and urine, and tenofovir diphosphate and emtricitabine in peripheral blood mononuclear cells will be determined using validated analytical methods developed by the investigators at the University of Colorado. Probenecid plasma and urine concentrations will also be measured using an in-house assay. Following completion of the study, the secondary aim will be accomplished via analysis of selected samples collected at baseline and following treatment. Those selected samples will be assessed for urinary markers of proximal tubulopathy (urine total protein, albumin, creatinine, phosphorus, retinol binding protein, and beta-2-microglobulin) and serum alkaline phosphatase, osteocalcin, procollagen type 1 N propeptide, cystatin C, and creatinine to determine if the probenecid boosting strategy does indeed lead to less potential renal and bone toxicity.