Rectal-specific formulation of tenofovir gel shows promising results early on

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Early-phase study reports looking at the use of a microbicidal tenofovir gel proven to reduce HIV infection during vaginal sex have shown promising results when used rectally.

The study results were presented at the 18th Conference on Retroviruses and Opportunistic Infections in Boston Monday. A strong antiviral effect was achieved when the gel was used daily over a week-long period. This was the first time that tenofovir gel has been shown to reduce the risk of HIV transmission during anal sex.

Rectal tissue biopsies showed significant protection among participants who used tenofovir gel daily for one week as compared to those in the placebo group. No protection was found in the rectal tissue samples of those who took a single dose of oral tenofovir, and while a slight antiviral effect was also noted in the rectal tissue samples of those who used a single dose of the gel, it was not statistically significant.

Side effects observed among two of the 12 participants included severe gastrointestinal side effects, including diarrhea and cramps. “In hopes of making tenofovir gel more acceptable to for rectal use, researchers have since modified the gel and are now testing it in another study,” according to a press release from the Microbicide Trials Network (MTN).

“These are early results, but help set the stage for current and future trials of rectal microbicides and the development of a rectal-specific formulation of tenofovir gel,” said Ian McGowan, MD, PhD, co-principal investigator of the Microbicide Trials Network and professor of medicine at the University of Pittsburgh. Dr. McGowan is leading the second study of the new gel formulation.

The CAPRISA 004 study results that came out in July 2010 showed that tenofovir gel applied vaginally before and after sex successfully reduced the risk of HIV transmission for high-risk women by 39 percent. According to the MTN press release, “The risk of becoming infected with HIV from unprotected anal sex may be at least 20 times greater than unprotected vaginal sex, in part because the rectal lining is only one-cell thick compared to the vagina’s multiple layers, making it easier for the virus to reach cells to infect.”

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