Investigators gave more details about the positive results of the Partners PrEP Study Tuesday at the 19th Conference on Retroviruses and Opportunistic Infections in Seattle. The study of 4,700 HIV discordant couples (where one partner is HIV-infected and the other is not) looked at the potential of two different antiretrovirals for pre-exposure prophylaxis (PrEP) for HIV-1 prevention versus a placebo among heterosexual men and women in rural and urban Kenya and Uganda. A data safety monitoring board recommended a discontinuation of the placebo arm in July 2011 due to definitive protection shown in the active drug arms of the study.
Dr. Jared Baeten, of the University of Washington in Seattle, presented the primary efficacy results of the PrEP interventions versus the placebo outcomes of the trial so far. During the course of the study 96 HIV-1 seroconversions occurred – 14 of which were retrospectively found to be HIV-1 infected at study enrollment, leaving 82 infections during the course of the trial. The placebo group had a significantly higher rate of infection with 52 of the total infections, leaving 13 infections in the FTC/TDF arm and 17 in the TDF only arm. That translates into 75 percent protection in the FTC/TDF arm and 67 percent in the TDF only arm as compared to the placebo.
Even looking at the sub-groups in the study that were considered at higher-risk of HIV infection, the study team found similar efficacy of the drugs in preventing transmission, Baeten said.
Although the majority of HIV uninfected persons who enrolled in the trial were men, the majority of infections occurred in women (45 of the 82 infections that occurred during the study). At enrollment 27 percent of couples reported unprotected sex in the past month. That declined during follow up and was similar across the study arms, hinting at the importance of the other HIV prevention services offered in the trial, which included safe sex counseling, HIV testing, free condoms, and testing and treatment for other sexually transmitted infections. There was also no evidence of behavioral risk compensation.
Adherence to study medication was very high among all groups – more than 97 percent of dispensed doses of the study medications were taken, and more than 95 percent of participants were retained in study follow up.
The active drug arms of the study are ongoing and will wrap up at the end of this year. They tested placebo arm for evidence of drug – and no suggestion of sharing has been found so far.