I am a gay MSM in NYC who just started Descovy. When I went to the New York health website it said that Truvada took seven days to reach protection for MSM but “It is unclear how long to protection for Descovy” Any thoughts on this? I was under the impression that Descovy, like Truvada, took 7 days to reach maximum protection.  Thanks!

Background for other readers -- you might already know:  Truvada and Descoby both are combinations of the antiretroviral drugs emtricitibine and tenofovir. The tenofovir formulations are different, which in turn results in different levels of drug circulating in the blood and other body fluids versus the concentrations inside HIV-susceptible cells. In addition, the Descovy version is much better absorbed overall and therefore is a smaller amount in each tablet (300 mg in Truvada vs 25 mg in Descovy). All in all, Truvada and Descovy are believed to be nearly 100% effective as post-exposure prophylaxis against HIV (PrEP).

However, the US Food and Drug Administration did not require data on time to reach full prevention effectiveness prior to marketing. Truvada has been available and on the market longer, and there has been time for post-marketing studies of time to effective prevention, i.e. 7 days. Such data are not yet available for Descovy. In theory, the time might be sooner and the overall effectiveness greater, which is why Descovy was developed in the first place. However, in absence of clear data, the NY State website statement is reasonable; it is exactly my advice as well. My understanding is that most HIV clinics and providers are telling patients they can rely on Descovy's effectiveness as PrEP after 7 days. But if you prefer to delay unprotected sex a bit longer -- perhaps 2 weeks instead of 1 week -- you're free to do so.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

As long as we are on topic, do you have thoughts about Descoy 2-1-1? I know that regimen has only been studied with Truvada and there seems to be a fair amount of conflicting thoughts online  about 2-1-1 in general