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PrEP Ineffective for Women? Study on Truvada for HIV Prevention Is Unexpectedly Cut Short

By Myles Helfand

April 18, 2011

A clinical trial investigating the use of pre-exposure prophylaxis (PrEP) to prevent HIV infection among women has been canceled after early results suggested the approach would be ineffective, according to a statement issued by FHI, which implemented the study.

The findings are unexpected, to say the least. It was just a few months ago that a trial known as iPrEx gave us solid evidence to suggest that PrEP -- the use of antiretrovirals by HIV-negative people to help prevent infection during high-risk sexual exposure -- was successful in reducing the risk of HIV infection among men who have sex with men (MSM). In fact, iPrEx was so successful that the U.S. Centers for Disease Control and Prevention (CDC) quickly created interim guidelines to help health care professionals decide whether (and how) to prescribe PrEP to HIV-negative MSM.

In its own statement on the cancellation of the FHI study, the CDC wrote:

"These preliminary results are disappointing, especially given that this approach has already been shown to be effective in reducing HIV infection among men who have sex with men (MSM). The well-conducted study included nearly 2,000 women at high risk for HIV infection in three African nations and sought to determine if a once-daily pill containing oral tenofovir and emtricitabine (FTC/TDF or Truvada) could protect women from HIV infection. While PrEP with FTC/TDF was not shown to be effective in preliminary analyses of these study results, it cannot yet be definitely determined whether this drug combination works, or does not work, to prevent HIV among women."

It's uncertain where we go from here. Other ongoing PrEP research may support or refute these findings; only time will tell. And we can hope that a deeper analysis of the FHI study (known as FEM-PrEP) will provide a logical explanation as to why Truvada would be effective as a prevention tool for MSM but not for women. (Early theories include poor adherence to the HIV meds and the possibility that, for whatever reason, oral Truvada just doesn't prevent sexual transmission of HIV vaginally as well as it prevents it anally.)

In the meantime, these findings are likely to make clinicians much more reluctant to prescribe Truvada to HIV-negative women at potentially high risk for HIV. Those who have been skeptical about the widespread use of PrEP will likely welcome this news; some feel the medical community has been too quick to embrace PrEP without fully accounting for its potential downsides. But you can't help but mourn this potentially major setback for PrEP, which, just a couple of months ago, seemed like it might be a promising new tool for women who may not have the option of using condoms with their male sexual partner.

Myles Helfand is the editorial director of and

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