Background:  Tenofovir (TFV) is effective in preventing HIV transmission in animal models, and is being investigated for pre-exposure prophylaxis in a number of populations. However, no comprehensive data exist describing TFV exposure in the genital tract. This is the first study to measure TFV extracellular and intracellular diphosphate (TFV-DP) concentrations in the genital tract of men and women from day 1 to steady-state.

Methods:  A non-blinded pharmacokinetic study was performed in HIV-1-infected subjects (9 men, 13 women). A subset (8 men, 1 woman) underwent 14-day monotherapy to assess TFV effects on genital tract HIV-1 RNA. For men, paired blood and genital tract samples were obtained 24 hours post-dose on day 1, 3, 5, and 7. At steady state (≥14 days), 10 blood and 5 genital tract samples were obtained over 24 hours. For women, 6 paired blood and genital tract samples were obtained over 24 hours on day 1 and at steady state. Intracellular concentrations were measured in mononuclear cells isolated from blood, semen, and cervical cytobrush samples using percoll or Dynabeads®. Genital tract extracellular concentrations were measured in blood, plasma, seminal plasma, or directly aspirated cervicovaginal fluid. Concentrations were measured by validated LC/MS/MS and LC/UV assays. Blood and genital tract HIV-1 RNA were measured by Roche Amplicor™ HIV-1 Monitor UltraSensitive and Nucli-Sens® HIV-1 kits. Data were analyzed using noncompartmental pharmacokinetic and nonparametric statistical methods. Data are presented as mean (SD).    

Results:  At 24 hours, intracellular TFV-DP genital tract-to-blood ratios in men for day 1 and 7 were 3.1±5.4 and 7.0±14.8, respectively. TFV-DP could not be detected in the genital tract of all women and some men due to low cell yields (<10⁶ cells/sample). TFV exposures were significantly greater (p <0.05) in genital tract than blood at both day 1 and steady state in men and women. Over 14 days in men, HIV-1 RNA decreased by 1.1±0.5 log₁₀ copies/mL in blood and 1.0±0.4 log₁₀ copies/mL in genital tract (p <0.05). In the 1 woman on TFV monotherapy, HIV-1 RNA decreased by 0.8 log₁₀ copies/mL in both blood and genital tract.

*Concentrations in genital tract > blood (p <0.05) 

Conclusions: From day 1 to steady state, TFV exposures were high in the genital tract of men (extra- and intracellular) and women (extracelluar). These extra- and intracellular genital tract exposures are the highest (relative to blood) among other ART reported to date. TDF monotherapy significantly reduced both blood and genital tract HIV-1 RNA over 14 days. The rapid achievement of high extra- and intracellular concentrations in the genital tract of men and women is encouraging, and supports further study of TDF in pre- and post-exposure prophylaxis trials.