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AIDS: Pre-Exposure Prophylaxis - 2004-03-05

A new study begins in May to determine whether a drug used to treat HIV infection can help prevent infection in the first place. The prevention method is called Pre-Exposure Prophylaxis, taking a single pill a day to block HIV infection in the event of risky sexual behavior. But there’s concern such a pill could actually encourage such behavior.

The concept of Pre-Exposure Prophylaxis is not a new one. For example, many travelers are given drugs to prevent malaria. But HIV is not transmitted by mosquito, but rather by sexual intercourse, as well as intravenous drug use and contaminated blood transfusions.

Keeping that in mind, Family Health International – a non-profit organization – will enroll volunteers in the United States and developing countries. These include Nigeria, Ghana, Cameroon, Malawi, Botswana and Cambodia. The drug being tested is Tenofovir also known as Viread. It’s been on the market since late 2001 and is often used in combination with other medications. It’s part of a class of drugs called Nucleoside Reverse Transcriptase Inhibitors. Some well known HIV fighting drugs in this category are AZT and Retrovir.

Dr. Ward Cates, president of FHI’s Institute for Family Health, says certain criteria will be used to find volunteers.

"There are a bunch of anthropologic measures that we use that indicate to us that HIV is being transmitted. And we go to those areas and offer people in a totally informed consent format, that makes participation entirely voluntary, the opportunity to participate in this trial. Where they will not know whether they’re getting a real drug or a placebo and therefore it’s very important to counsel them to continue or even increase their levels of safer behaviors to the extent we can’t."

This will be the first Pre-Exposure Prophylaxis trial of an anti-retroviral drug, or ARV. There have been studies of Post-Exposure Prophylaxis, whereby ARV’s are given to people who may have been exposed to HIV through an accidental needle stick at a hospital or through rape.

Dr. Cates says there is concern that if people take the drug they may be less careful in their sexual behavior. What he calls “disinhibiting previous safer behavior.”

He says, "We’re very much aware in any of the HIV prevention trials that we do – again whether it’s this Pre-Exposure Prophylaxis or whether its vaccines or circumcision to prevent HIV infection – we have to be very careful that we build on existing safer behaviors and not disinhibit those particular safer behaviors."

On the other hand, if successful, it could be used by women whose partners refuse to use condoms.

Among those closely following the Tenofovir trial is Gus Cairns, Editor-in-Chief of Positive Nation, a British HIV and sexual health magazine. He says Pre-Exposure Prophylaxis is a very encouraging development. But he also has concerns about behavior change.

"One is the whole issue about whether it will cause people to throw away the condoms. You know? The whole thing of ‘oh it’s ok. We don’t need to use a condom because I’m on the AIDS pill.’ And my feeling about that is it may well happen in the longer term. We need to make a comparison here with the common use of the contraceptive pill in women. When that came along, a lot of women took to it and it became a great boon in many cases for emancipating women. But it doesn’t mean that everybody uses it and it’s not foolproof."

Mr. Cairns says another concern is that people may think Tenofovir will prevent other sexually transmitted diseases. It won’t. And he says there could be an increase in cases of syphilis and gonorrhea.

He says, "The way we have to do it is that we as a community of people who are affected by the virus one way or another have to set conditions about exactly how this intervention is used. Because my worry is that we’ll start seeing advertisements for Viread, which is the trade name for Tenofovir, like you see it for Viagra now. That it will become sort of a gray market drug circulated around and I don’t want to see that happening. I think that could be very dangerous."

The editor-in-chief of Positive Nation magazine says the preventive treatment probably won’t be available for everyone because it will likely be expensive.

Family Health International says the study will last 18 months - six months for recruitment of volunteers and twelve months to follow-up. The main goal of the study, despite the drug’s possible prophylactic effect, is to determine whether it’s safe to use on uninfected people. It hopes to have some results to report by mid 2006.