Stop and Go PrEP: Will it Work?

Published: March 22, 2013

A couple of months ago, I wrote about the question of when somebody taking PrEP might consider discontinuing its use. A few readers e-mailed me to ask a related but different question:  what if you stopped taking Truvada when you weren’t having sex, and started taking it again later? Scientists call such an approach “intermittent” use of PrEP.

The idea makes some amount of sense – especially to someone like me who rarely has sex in the town in which I live, in the middle of effing nowhere, in the frozen tundra of the Midwest. The bulk of my sex happens when I’m on the road, either for business or just simply for sexual tourism. Could it make sense for guys like me to only start taking PrEP before their next vacation, and stop taking it a few weeks after you get home?

Whatever you want to call this approach – intermittent, stop and go, on demand – the first thing to know is that we don’t have clear answers yet. The biggest PrEP studies were intended to test whether it was effective to take the drug every single day. There is a French clinical trial aimed at testing whether this idea would work, but it’s only recruiting in Paris and Lyon. This trial is particularly controversial because some of the people in the study are getting placebos rather than the real deal. Generally, once a trial has shown an intervention to be effective, it’s deemed unethical to continue giving some people a placebo. In this case, the argument from researchers was that it is not yet known whether on demand PrEP is effective and thus it is ethical to assign some people a sugar pill. To say the least, I’ve got mixed feelings about that argument (and from the gossip I hear, so do French gay guys – little birds tell me they’re having trouble finding guys to sign up). 

Luckily, a clinical trial isn’t the only way to address these questions. At the 20th Conference on Retroviruses and Opportunistic Infections (CROI) in Atlanta two weeks ago, Bob Grant – the man behind the iPrEX study – presented preliminary data that grappled with these questions based on his ongoing study of the guys in iPrEX. Grant reports that some guys in the study moved through “seasons of risk,” or periods in their life when they were at greater risk of sexually acquiring HIV than others. This is a little different than planning a weekend of debauchery, of course, but the idea is similar: risk for HIV is not a constant throughout one’s life. If that’s the case, then it may make sense that PrEP might not also need to be a constant.

Indeed, he reports that at any given moment, about 30% of iPrEX participants had zero sexual partners in the last three months. Not surprisingly, these participants were often the same ones who weren’t taking Truvada every day. It doesn’t take a nuclear physicist to figure out that taking a pill every day to prevent HIV when you haven’t had sex in months is overkill – it’d be a bit like wearing a condom when you went shopping with your grandma!

But exactly how long before you plan to get laid, and how long after, should you take Truvada? While we don’t have perfect data to show that starting and stopping PrEP is as effective as daily use, Dr. Grant’s team informs his iPrEX participants that you should start taking Truvada seven days before you think you might have sex. This gives ample time for the drug to get into your system. As for afterwards, Dr. Grant recommends taking Truvada for four weeks after your last potential exposure. It might be that future research shows you only need three days before and two weeks after – but for now, it makes sense to err on the side of caution.

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