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Ipergay PrEP study results published
Gus Cairns, 2015-12-02 11:00:00
The results from the Ipergay study of intermittent pre-exposure prophylaxis (PrEP) were published in the New England Journal of Medicine (NEJM) on 1 December, World AIDS Day. The journal-published results are little changed from those presented at the CROI conference last February by principal investigator Jean-Michel Molina but the researchers make a number of additional comments and are notably cautious about not over-interpreting a study that only had 400 participants – very small for a prevention study – and an average of nine months’ follow-up.
Despite this, Ipergay represents a major innovation in PrEP. It is the first, and so far only. randomised study to show that PrEP can be just as effective as daily PrEP if it is given as an intermittent regimen that users only take when anticipating sex.
To summarise the results: in Ipergay 400 gay men and transgender women were randomised to either take Truvada (tenofovir/emtricitabine) or a placebo.
The regimen that participants were told to take was a double dose (two pills) 24 to two hours in advance of anticipated sex, and then a pill on both of the two days following sex. If they continued to have sex, they were to keep taking one pill a day until two days after the last sex. If they restarted sex, they had to take a double dose if there had been more than a week since the previous sex.
The use of a placebo was somewhat controversial in Ipergay as some activists felt that the effectiveness of PrEP had already been sufficiently demonstrated by the iPrEx study of 2010. However effectiveness in iPrEx was only 42% overall, and the writers comment that “The use of a placebo was deemed to be justified because of the inconsistent efficacy of PrEP in previous trials and the moderate efficacy in the iPrEx trial.”
There were 19 HIV infections during the whole Ipergay trial period but three of those were determined to have happened shortly before participants started taking PrEP/placebo. There were 16 infections in men allocated to placebo and two in men allocated to PrEP.
In fact neither of these men had taken PrEP, or hardly any, in the two-month period before they tested positive (in Ipergay, clinic visits were every eight weeks). One new detail added in the NEJM piece is that participants were asked to return unused pills and on the visit they were diagnosed, these two participants returned respectively 60 and 58 out of the 60 pills given to them two months previously.
The 16/2 difference in infections represents an 86% (95% confidence interval: 40%-98%) reduction in the risk of HIV infection in the trial participants allocated to Truvada. HIV incidence in the trial was 6.6% a year in placebo recipients and 0.91% in Truvada recipients. The 6.6% is more than double the 3% incidence anticipated before the trial, though not as high as the 9% seen in the deferred-PrEP arm in PROUD.
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