Physorg.com -- A gel developed to protect against HIV during vaginal sex produced a strong antiviral effect when used in the rectum, according to an early-phase study presented today at the 18th Conference on Retroviruses and Opportunistic Infections (CROI). The results, based on rectal tissue biopsies sampled from HIV-negative men and women who used the product daily for one week, provide the first-ever evidence that tenofovir gel could help reduce the risk of HIV from anal sex, even though the vaginal gel formulation may not be optimal for rectal use.