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Overall PrEP effectiveness in iPrEx OLE study 50%, but 100% in those taking four or more doses a week
Gus Cairns, 2014-07-22 07:40:00
The open-label extension of the iPrEx study of pre-exposure prophylaxis (iPrEx OLE) reported its main findings at the 20th International AIDS Conference (AIDS 2014) in Melbourne, Australia today, and published simultaneously in The Lancet.
Recruitment, retention and adherence data were reported a year ago in Kuala Lumpur but now we know how this translated into efficacy. The study recruited 1225 participants, of which 847 elected to take PrEP.
The group of gay men and transgender women in this study who elected to take a daily tenofovir/emtricitabine (Truvada) pill had half as many HIV infections (relative risk = 0.51) compared with a comparator group of people who elected to stay in the study but not to take PrEP. They also had half the HIV infection rate (relative risk = 0.49) of people in the placebo arm of the original iPrEx randomised controlled trial (RCT).
As has been seen in other studies of pre-exposure prophylaxis (PrEP), as well as in the original iPrEx RCT, the primary determining factor when it came to the efficacy of PrEP was adherence. All participants in iPrEx OLE had their level of adherence calculated from drug levels observed in blood samples.
PrEP had so significant efficacy in people who took fewer than two doses a week. However, the efficacy of PrEP was 84% in people who took 2-3 doses a week – there was only one infection in this group – and no infections at all were seen in people taking at least four doses a week. This 100% efficacy translates into a minimum efficacy of 86% if the statistical uncertainty of the result is taken into account.
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