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Report from Melbourne: The role of adherence in PrEP

It should come as no surprise that new data from the iPrEx open label extension shows that 100% of people taking the drug 4 or more times per week were protected, whereas the efficacy rate was much less when people took PrEP less often.

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 randomized controlled trial (RCT).As has been seen in other studies of pre-exposure prophylaxis (PrEP), as well as in the original iPrEx, 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 no 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.
"If people were at higher risk they took more PrEP and adhered to it shows that people who are at risk can take reasonable and appropriate decisions on their own behalf," according to Robert Grant, study author.

Grant RM et al. Results of the iPrEx open-label extension (iPrEx OLE) in men and transgender women who have sex with men: PrEP uptake, sexual practices, and HIV incidence. 20th International AIDS Conference, Melbourne, abstract TUAC0105LB, 2014.

Note: This study was published in The Lancet Infectious Diseases concurrently with its presentation at the conference.

Source: Reporting from Melbourne, Australia, for the PRN News: Bill Valenti, MD