Results of a study released today during the Conference on Retroviruses and Opportunistic Infections being held in Boston indicate that a medicinal gel containing the HIV drug tenofovir could help prevent the transmission of HIV during anal sex.

According to a report posted today on, the same gel has been shown in other studies to reduce the rate of HIV transmission during vaginal sex. The risks of HIV transmission during anal sex can be as much as 20 times higher than during vaginal sex.

In the study, participants were given either the tenofovir gel, a placebo gel or a tenofovir tablet to be taken orally. Researchers then took anal tissue from each group and exposed the tissue to HIV. The study indicates that of the three, the tenofovir gel significantly reduced the rate of HIV transmission, and that it provided the most protection after a seven-day course of treatment.

Researchers said they are also “tweaking” the gel’s inactive ingredients to hopefully eliminate some of the side effects — such as severe diarrhea and lower stomach cramps — reported by study participants who used the tenofovir gel.

Reuters reports that a separate, mid-stage study, comparing the oral and gel forms of tenofovir in African and American women, indicates that daily use of tenofovir gel resulted in a more than 100-times higher concentration of active drug in vaginal tissue compared with use of an oral tablet.