April 22, 2011
On April 18, 2011, researchers stopped a study that used a daily pill to prevent HIV infection in heterosexual women. Early results from the study, called FEM PrEP, revealed it could not show that Truvada would work in this study population. The researchers cautioned that this doesn’t mean it couldn’t work for women in other studies.
FEM PrEP had so far enrolled 1,951 African women of its planned 4,000 participants. Half had taken the HIV medicine Truvada (emtricitabine + tenofovir) every day while the other half took a placebo pill. All of the women were also using hormonal contraception.
After an early review, 28 infections had occurred in both groups. As well, 9% of the women had become pregnant, which suggests issues with them taking the Truvada and/or contraception as prescribed. The pregnancy rate was higher in the Truvada group.
The reasons why Truvada wasn’t effective in FEM PrEP are unknown at this time. However, some possibilities include: the women did not take the pill as prescribed despite them stating otherwise; unknown drug interactions between Truvada and the contraceptives used; the lack of entry into vaginal and cervical tissue by Truvada; the strategy doesn’t work in women;Â or it simply did not work in this study but may be shown to work in other studies.
These results greatly contrast the two major PrEP breakthroughs in 2010 from the CAPRISA and iPrEX studies. In July, CAPRISA reported 43% fewer infections when women applied a vaginal gel that contained the HIV drug tenofovir before and after sex. In November, iPrEX reported 44% fewer infections in high-risk gay men who took oral Truvada daily. In both studies, even fewer infections occurred when the products were used 90% of the time.
Although the FEM PrEP results are discouraging, they underscore the need to conduct a range of PrEP strategies in various communities. Of note, while Truvada appears to enter rectal tissue well enough to prevent HIV – as seen in iPrEx – the pill may not be able to provide the same protection vaginally for women. It will take several months to fully analyze the data, including examining the blood samples that were collected monthly.
For more information, read the researchers’ statement.