Research into how the body processes Truvada (tenofovir/emtricitabine) suggests that experimental non-daily-dosing protocols for pre-exposure prophylaxis (PrEP) may offer high protection against HIV infection through anal sex. Vaginal sex protection remains up for debate. After male participants in one study were given a double dose of Truvada, tests suggested that the tenofovir element reached a detectable concentration in rectal tissues after 24 hours. Another study examined the metabolization of daily Truvada and found that tenofovir levels in cervical tissue cells apparently only ever reached a level one-tenth that of rectal tissue cells. Maximum drug levels in the rectum were reached after just five days of Truvada, compared with 10 to 12 days in the cervix.One, two and three daily doses of Truvada led to a respective 77 percent, 89 percent and 96 percent reduction in anal sex HIV risk. The corresponding figures for vaginal sex protection are still unknown.