CDC U.S. Tenofovir Extended Safety Trial
In 2010, CDC completed a Phase II extended safety trial examining the clinical and behavioral safety of once-daily oral PrEP with tenofovir and adherence to the drug among gay and bisexual men in the United States.
The study was conducted at three sites in collaboration with the San Francisco Department of Public Health, the AIDS Research Consortium of Atlanta, and Fenway Community Health in Boston. The study enrolled 400 HIV-negative MSM who reported having had anal intercourse with a man in the prior 12 months. Participants were randomly assigned to one of four study arms. Two arms received either tenofovir or placebo immediately upon enrollment, while the other two arms received either tenofovir or placebo after nine months of enrollment. This design allowed researchers to compare risk behaviors among those taking a daily pill and those not taking pills.
Preliminary analyses suggest no serious safety concerns. While analysis of behavioral safety data are not yet complete, preliminary analyses suggest there was no increased risk in men taking a study pill compared to those not taking a study pill during their first nine months of study participation. Additional analyses of clinical, behavioral, and adherence data are underway.
Education and Enrollment of Trial Participants
Understanding the potential impact of a daily preventative drug regimen on HIV risk behaviors will be critical, should pre-exposure prophylaxis prove effective in reducing HIV transmission. One of the greatest risks, as efforts progress to identify new biomedical prevention approaches that may only be partially effective, is that individuals at risk will reduce their use of existing HIV prevention strategies. It will therefore be crucial to reinforce proven behavioral prevention strategies, both within and beyond these trials. CDC trials are taking multiple steps to address this issue during the education and enrollment of trial participants and through ongoing participant counseling.
It is critical to ensure that participants understand that trial participation may not protect them from HIV infection — either because they may receive a placebo or because they may receive a study drug, the efficacy of which remains unproven. This and other key aspects of the trial, including the potential risks and benefits of participation, are explained to potential volunteers in the language of their choice, prior to their enrollment. To ensure participants fully understand all aspects of their participation, all volunteers are required to pass a comprehension test prior to providing written informed consent. Study participants are also free to withdraw from the trial at any time and for any reason.
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