Early today, results were released from two independent clinical trials evaluating the efficacy of PrEP among heterosexuals at risk of HIV infection. In both cases, a statistically significant reduction in risk of HIV acquisition was documented in the trial participants receiving PrEP (consisting of the antiretroviral drugs Viread or Truvada) compared to placebo.
The larger of the trials, named Partners PrEP, was conducted by scientists at the University of Washington. It enrolled 4,758 HIV serodiscordant couples in Kenya and Uganda and randomized the HIV-negative partners to receive either Viread (tenofovir), Truvada (a combination of tenofovir and emtricitabine in a single pill) or placebo. A total of 78 HIV infections occurred: 47 in the placebo group, 18 in the Viread group and 13 in the Truvada group. This equated to a 73% reduction in risk of HIV acquisition for those assigned to Truvada (95% confidence interval 49-85%) and a 62% reduction among those in the Viread arm (95% confidence interval 34-78%). The statement on the trial results notes that no significant side effects were observed but does not provide details, additional information is expected to become available next week at the IAS Conference on HIV Pathogenesis, Treatment and Prevention in Rome.
The second trial (called TDF2) was conducted by the US Centers for Disease Control (CDC) in Botswana. The population was not couples in this case, but 1,200 sexually active men and women aged 18-39 (54.7% male/45.3% female) in Gaborone and Francistown. Participants were randomized to receive either Truvada or placebo. There were a total of 33 HIV infections during follow-up: nine among the 601 individuals in the Truvada group and 24 among those assigned to placebo. The reduction in risk of HIV acquisition was 62.6% (95% confidence interval, 21.5-83.4%), a statistically significant result. In an analysis restricted to participants known to have a supply of Truvada (i.e. those who had not missed a study visit at which 30-day supplies of drug were dispensed), efficacy was reported to be 77.9% (95% confidence interval 41.2-93.6%). Similar efficacy was observed in both men and women. The side effects reported more often in the Truvada arm compared to placebo were nausea, vomiting, and dizziness.
Back in December 2009, the CDC issued statements indicating that the incidence of HIV infection in the TDF2 trial population was low and that the study was focusing on safety and adherence because it was “very unlikely” that efficacy could be demonstrated; however, in announcing the results today the researchers noted that “because PrEP was highly effective in this population, the study was able to draw conclusions about overall efficacy, even with a relatively small number of infections occurring in the study population.” As with the Partners PrEP trial, more details are expected to be presented at the IAS conference next week.
A collection of statements and other information from the trial sponsors can be found on the AVAC website. AVAC is also hosting a conference call tomorrow (July 14) with the trial investigators; information on how to register is on the same page.
Today’s news contrasts with the recent announcement that a trial of Truvada as PrEP in women (the FEM-PrEP study) could not show efficacy due to similar infection rates in the active and placebo arms. The reasons for the different outcome remain to be elucidated, but could relate to differences in adherence and/or unsuspected interactions between Truvada and the types of contraceptives being used by participants (a significantly higher rate of pregnancy occurred in the Truvada arm of FEM-PrEP, and researchers are investigating what may have caused this).
Selected media stories:
AIDSMap - Two major studies show that HIV drugs prevent infection
Washington Post - Two studies show that drugs used to treat AIDS can be used to prevent HIV infection, too
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