HIV/AIDS: Microbicide gel could stop spread of HIV during anal sex
A rectal microbicide is important for men who have sex with men and women who engage in anal sex
NEW YORK, 1 March 2011 (IRIN) - A microbicide gel designed initially for vaginal use may be effective in safely preventing the spread of HIV when applied to the rectum prior to anal sex, according to preliminary research presented by the Microbicides Trial Network (MTN) this week.
The hopeful findings, presented on 28 February at the 18th Conference on Retroviruses and Opportunistic Infections
in Boston, indicated that the vaginal anti-HIV gel had an equally strong antiviral effect when used in the rectum.
The study marks the first time a gel has been found to ward off the spread of HIV in the rectum, which due to its thin lining makes people engaging in unprotected anal sex
20 times more likely to contract HIV, according to Ian McGowan, a professor of medicine at the University of Pittsburgh and the lead researcher of the study.
The continuing research - and possible eventual manufacture of a commercial anti-HIV rectum gel - could have monumental effects for both at-risk men who have sex with men
(MSM) and women who engage in anal sex.
"My hope and expectation is that the rectal field, over the next two or three years, is really going to start looking at effectiveness studies and we will be crossing into a newer field, really," McGowan told IRIN/PlusNews. "We are very much about equal opportunity - the rectum is a very vulnerable site and this is important for MSM and also women having anal sex."
McGowan, a co-principal investigator of the US-based Microbicides Trial Network, co-led the initial study, known as RMP-O2/MTN-006, testing the vaginal tenofovir microbicide gel on 18 sexually abstinent, HIV-negative men and women. McGowan and his co-researcher, Peter Anton of the University of California, Los Angeles, also administered oral doses of the antiretroviral drug, tenofovir.
"We took biopsies from the rectum, sent them to the laboratory and in the test tube added the virus," explained McGowan. "The rate of infection - the magnitude of infection - in the biopsies was significantly lower than the biopsies that had not seen the drug."
The study had its complications, however. Only 25 percent of men and women who used the gel said they liked it, and two of the 12 research participants experienced gastrointestinal side effects, including diarrhoea and lower abdominal cramping.
"The lining of the rectum is much more fragile than the vaginal epithelium, so we can't be certain a product like tenofovir gel that is safe for vaginal use will be completely safe to use in the rectum," said Charlene Dezzutti, associate professor of obstetrics, gynaecology and reproductive sciences at the University of Pittsburgh School of Medicine and principal investigator of the MTN Network Laboratory, in a media release.
While 75 percent of the participants said they would still use the gel as an HIV-preventative method if it were available, the negative physical effects of the vaginal tenofovir gel prompted researchers from CONRAD, a division of the Eastern Virginia Medical School which holds the rights to the gel, to alter its makeup.
The investigators decreased the amount of glycerin, a common additive in gel-like substances, resulting in a gel that is equally effective in preventing the spread of HIV, as well as less likely to prompt rectal tissue cells to release water.
Follow-up study on new gel
McGowan is now leading the follow-up study, MTN-007, testing the gel on 37 participants - a number that is expected to scale up to 60 - to gauge its usability and safety. Initial laboratory tests found the gel to be less harmful to rectal tissue than the vaginal tenofovir gel, but just as effective in stopping the spread of HIV.
Currently 20 percent of the participants are female. It is not yet clear if the participants are experiencing negative physical effects from the new gel, since the study is blinded, according to McGowan. It also has yet to be determined for how long the gel could be effective and how frequently it must be reapplied, added McGowan, who noted that he hopes to conclude the study within the next two to three months.
If this initial testing proves successful, McGowan will expand the study from short-term, daily one-week exposure to the gel, to three and six month usage. If found to be safe and acceptable to users, the rectum microbicide gel could be on track to get licensed and then eventually distributed by 2016 or 2017.
The two groundbreaking rectum microbicide studies follow 10 years of research and five years of technical trials devoted to rectum microbicides, according to McGowan. That places research on rectum microbicides around 10 years behind that of vaginal microbicides. Last year
, it was reported that a vaginal gel containing tenofovir was 39 percent effective in reducing a woman's HIV risk when used for about three-quarters of sex acts and 54 percent effective when used more consistently.
"This field is newer and the study we are doing is smaller and somewhat cheaper, so we haven't quite stretched the system yet," McGowan said. "I think funding at the moment is adequate for where we are, but as we move into bigger studies there will have to be an increase in funding to match that. But I don't think something like funding is going to hold this field back from moving to a future stage."