27 April 2011 

PrEP study closes – questions remain unanswered

Pre-exposure prophylaxis, or PrEP, is currently being studied as a potential method for a person who is at risk of HIV infection to reduce their risk of becoming infected. It involves taking anti-HIV medications on a regular basis. One study, known as FEM-PrEP, was recently closed before it was completed. The trial studied the daily use of a Truvada pill as PrEP among 1,951 HIV-negative heterosexual women in Eastern and Southern Africa. In this study, half of the women were given Truvada while the other half were given a placebo.

The decision to stop the study was made by an Independent Data Monitoring Committee (IDMC). These committees are responsible for reviewing preliminary data from ongoing trials and deciding whether or not the trials should continue. The FEM-PrEP study was stopped after the committee found that an equal number of women had become infected with HIV in both the Truvada and placebo groups (28 infections in each group). The committee concluded that, even if the trial was allowed to continue to completion, it would not be able to determine if taking Truvada daily was effective. The study was not stopped for reasons related to safety or ethics or as a result of problems with the design or implementation of the clinical trial.

These results were disappointing and also surprising. Last year a similar study, called the iPrEx trial, found that the daily use of Truvada reduced the risk of HIV infection through anal sex when used by men who have sex with men. The unexpected FEM-PrEP results show that the success of an intervention in one population does not necessarily mean it will be successful in another population. This is why it is important for research studies to examine the effectiveness of an intervention in different populations.

Based on the preliminary data from the FEM-PrEP study, researchers do not know whether or not Truvada will be able to prevent HIV infection in women who are exposed to this virus through sex.  There are several theories that may explain why there was no difference in the number of HIV infections between the Truvada and placebo groups. One possible explanation may be that women in the Truvada group were not taking their Truvada pill regularly. Another possibility is that daily Truvada is not effective at reducing the risk of HIV transmission through vaginal sex for reasons that are not yet clear.

An in-depth analysis of the results, including information on adherence, is expected within the next few months. This analysis will hopefully be able to answer some of the questions raised by this study.

—James Wilton

For more information on PrEP:

FEM-PrEP Study website

CATIE Prevention in Focus article on PrEP

CATIE fact sheet on PrEP

CATIE news story on iPrEx trial