PrEP for HIV Prevention

Another blog post on HIV . . . it’s sort of my thing :p (and the focus of my thesis!)

On May 10^th the Antiviral Drugs Advisory Committee of the US FDA debated whether an anti-HIV drug currently used as an antiretroviral treatment should be approved as a prevention method for uninfected people. It was recommended to the FDA that the drug, Truvada (made by Gilead Sciences), be approved for pre-exposure prophylaxis (PrEP).

PrEP means that the drug is taken routinely by uninfected people at high risk of becoming infected with HIV. It has been shown that taking the drug daily can lower risk of infection by more than 90% in two target groups – men who have sex with men; and uninfected heterosexual (men) with a long-term, HIV positive partner. However, clinical trials of the drug in heterosexual women have failed. (Also, in reading another article about this, it was claimed risk was lowered only by 42% and 73% in separate trials...)

PrEP (like birth control) would need to be taken daily to be effective. And, if adherence is low this could have disastrous consequences, particularly if a backup method of prevention (condoms) is not used. As I mentioned in my last HIV post, the virus replicates really quickly, and doesn’t make perfect copies of itself, leading to mutated forms of the virus. Some of these mutants could be resistant to Truvada. So, if you are not using PrEP as prescribed and have a partner that is HIV positive, it is likely that you will become infected with the virus. If you continue to take the PrEP irregularly, you are putting yourself at risk of being infected with drug-resistant HIV, which would likely make treatment more difficult. Of particular note is that HIV treatment with Truvada must be undertaken in combination with other antiretroviral drugs to prevent resistance.

During the clinical trials participants were monitored monthly for HIV infection, using the most sensitive test to detect HIV, so that PrEP could be stopped upon infection to prevent resistance. A few cases of infection were seen in the trial participants, and just over half of them developed resistance. This testing should be continued for those that are taking Truvada for PrEP, but this testing was not included in the recommendation to the FDA. Without regular testing, it is possible that HIV could be transmitted to someone taking PrEP (remember, it isn’t 100% effective) and they wouldn’t know about it, so they would keep taking the antiretroviral. This will lead to development of a resistant virus, which will create a lot of problems for further treatment once the virus is detected.

I did a PubMed search and wasn’t able to find any clinical trial papers about Truvada, which I would really like to be able to read before forming an opinion on this, particularly since Science and Nature report two different statistics for protection levels. I think this approval of Truvada could drastically lower HIV prevention rates, if used properly (and if affordable!), however, it could also be disastrous if used improperly (particularly without regular HIV screening). Condoms are more effective at preventing HIV transmission and I highly recommend them because they also protect against other STI’s and pregnancy. But, for those who are unable to use condoms for various reasons (particularly women in developing countries), Truvada represents a new hope for HIV prevention.

Christina