AIDS 2014: Intermittent and 'On-Demand' PrEP

Paul E. Sax, MD


August 15, 2014

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This is Dr. Paul Sax from Brigham and Women's Hospital and Harvard Medical School. Today I would like to discuss 2 interesting studies[1,2] that came out of the AIDS 2014 meeting, which just took place in Melbourne, Australia.

Both of these studies are looking at pre-exposure prophylaxis (PrEP) with tenofovir/FTC. The first study is the open-label extension of the iPrEx study,[1] which is the pivotal trial demonstrating the efficacy of tenofovir/FTC for PrEP. Tenofovir/FTC was given as a daily dose in this study, but not all participants took the medication, and it has been shown multiple times in this study and others that adherence is the key determinant of success.

They looked at the blood levels of tenofovir in the study and correlated them with protection, and found that blood levels above a certain level led to 100% protection. Then they did modeling of adherence and correlated the blood levels for 100% protection to taking at least 4 tablets a week. It may be that the men in that study who took 4 or more tablets weekly were taking their PrEP intermittently in times of increased risk, and that leads us to our second study, which is the IPERGAY study.[2]

IPERGAY is being conducted in France in sexually active, high-risk men who have sex with men, looking at an on-demand strategy of PrEP using the active drugs tenofovir/FTC and comparing it with placebo.

The men are instructed to take 2 tablets 2-24 hours before having sex and 1 tablet daily for the next 2 days for this on-demand strategy. At the Melbourne meeting, the investigators did not present the results (they are planning to enroll 2000 men) but they presented the pharmacokinetics of the first 129 participants. They demonstrated that 86% of the men had detectable tenofovir concentrations in a range that would be protective.

This tells us that the men who are at the highest risk are probably taking something equivalent to daily PrEP, whereas those who are not at the highest risk are perhaps taking the drugs infrequently. This may turn out to be a more reliable strategy, or at least one that is easier for people to adhere to. Alternatively, it may be easier to just recommend daily PrEP, as is currently recommended by the Centers for Disease Control and Prevention.

Those 2 studies on PrEP received the most attention at the conference. The open-label extension study has just been published in Lancet Infectious Diseases,[3] and there is an excellent editorial by my friend and colleague, Dr. Raphael Landovitz.[4] The IPERGAY study is ongoing, and we don't yet have protective efficacy data.

Thank you very much for listening. I look forward to speaking to you again about other highlights from the meeting.


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