July 21, 2015

Non-daily PrEP regimens provide extra options, but adherence is often better with daily dosing

Written by Roger Pebody

This article originally appeared on the NAM website.

For some people in some settings, less frequent PrEP regimens with doses linked to sexual activity are feasible, with high numbers of sexual acts protected by PrEP, studies that were presented on Monday to the 8th International AIDS Society Conference in Vancouver show.

This may give people, who want to use PrEP, and their doctors additional options, allowing people to find a pattern of taking PrEP that best suits them. But the studies also found that more people are able to adhere to daily PrEP than non-daily regimens. Further, the actual effectiveness of non-daily regimens remains uncertain.

The studies presented today were in part inspired by the French IPERGAY study, so far the only study to demonstrate that a schedule of non-daily PrEP, with doses before and after sex, could be effective. (There were 86% fewer infections). However IPERGAY was conducted in a population of gay men who tended to have sex quite frequently. To prevent transmission during anal sex, four doses a week appear to be almost equivalent to seven doses. But it’s possible that people who have sex less frequently – and therefore take pills less frequently – will have lower levels of the drug in the body that are not protective.

Presented in Vancouver in a late breaker session on Monday afternoon, HPTN 067/ADAPT is a trio of three randomised trials, investigating the feasibility and acceptability of different PrEP regimens with three distinct populations, in Bangkok, Harlem (New York) and Cape Town. The studies give insights into patterns of use and adherence but were not designed to answer questions about effectiveness. Larger, phase III trials would be needed to do that.

The researchers found that in a group of well-educated, motivated Thai gay men, each of the three PrEP regimens tested were feasible, acceptable and likely to protect against most exposures to HIV. The non-daily regimens required far fewer pills to be taken.

Challenging social circumstances were more commonly experienced by participants in Harlem and Cape Town. Adherence was generally not as good in these two locations. Moreover the daily regimen resulted in better adherence and likely protection against HIV than the non-daily options.

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