One of the exciting, if controversial, advances in HIV medicine is the use of antiretroviral medications to prevent infection -- pre-exposure prophylaxis (PrEP). The previously published iPrEx, TDF2, and PARTNERS studies established the beachhead of tenofovir/emtricitabine (TDF/FTC, Truvada) and TDF-only PrEP in adherent patients, as well as TDF vaginal gel (in the CAPRISA 004 study), leading to U.S. Food and Drug Administration approval of tenofovir/emtricitabine for PrEP in 2012.
The VOICE study randomized over 5,000 HIV-uninfected women to receive oral TDF, oral TDF/FTC, oral placebo, vaginal TDF gel or vaginal gel placebo. The data safety monitoring board had previously halted the oral TDF and vaginal TDF gel arms due to an inability to demonstrate a reduction in the acquisition of HIV. The final results of the study were presented at CROI.
It appears that poor adherence was the explanation for the overall treatment failure; while more than 90% of participants reported adherence to the regimens, TDF was detected in only 25% to 30% of the samples, and 50% to 58% of the participants never had detectable TDF plasma levels.
These results are consistent with the previously reported FEM-PrEP study and highlight the requirements (and unmet needs) of adherence to PrEP regimens. Clearly, there are opportunities in PrEP for long-acting regimens or strategies that require minimum adherence.
PrEP, when adhered to, appears to be effective across multiple risk groups. The Partners PrEP study examined 4,758 heterosexual serodiscordant couples randomized to receive oral TDF, TDF/FTC or placebo. Analysis presented at CROI showed that among higher-risk heterosexuals (female, having a older male partner, having a partner with an HIV RNA >50,000, age <30, or having unprotected sex), including groups of only higher-risk women, PrEP was similarly effective.
The data strongly argue against the hypothesis that oral PrEP efficacy might be reduced in those at higher risk of acquiring HIV-1 because of greater viral exposure.
Which other studies presented at CROI 2013 will have lasting impact long after memories of the conference itself have faded? Read more of Dr. Llibre and Dr. Young's top picks.
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