Has PrEP ever failed?

Dear Bob,

I am a research educator and advocate that has done and continues to do a lot of work around PrEP. I believe I heard you say that not one case anywhere had been identified where a patient who had blood levels consistent with daily dosing seroconverted. Is my memory correct? Could the same thing be said about blood levels consistent with 4 does / week?

Educator and Advocate


Dear Educator and Advocate,

PrEP is highly effective when used, although there is no guarantee that PrEP will work all the time.   We do not make guarantees in medicine, and after 30 years working in HIV research and clinical care, I have learned to “never say never.”

I encourage people to think about their sexual goals and to make a plan for what is desired, including safety, remaining free of HIV and other sexually transmitted infections, pleasure, intimacy, fun, relationships, and so much more.  Intimate sex is a powerful opportunity for human connection, which is our power.

I think you are right to be curious about any time that PrEP appears to fail.  Let us review these situations.

In the iPREX clinical trial and the iPREX OLE demonstration project, we did not see any seroconverter with drug levels indicative of use of 4 or more tablets per week.  In the analysis of FEMPREP seroconverters (a trial of women), none had drug levels indicating use of 6 or more tablets per week.

There is one seroconverter recently published from the Partners PrEP trial of heterosexual men and women where there was some drug detected in blood plasma at every visit.  Because blood plasma is a poor indicator of adherence, no one can say how many tablets were used per week, only that at least one tablet was used in the days before each clinic visit.  What matters for HIV prevention is how many tablets were used before sex, not how many were used before the clinic visit.  Like flossing, we recommend that PrEP be used every day, and not just before seeing your doctor.

In the PROUD trial, Ipergay trial, and Partners PrEP Demonstration project, all reported at the CROI conference in February 2015, there were a total of 7 seroconverters in the active arms.  Six of the 7 had stopped PrEP completely months before their seroconversion, and one seroconverted in the first few weeks of PrEP use, and may have been infected before PrEP was started.

In clinical practice, I have heard of a few seroconverters who had received PrEP in the past – it is never clear or  documented how adherent they have been.



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Posted on

April 15, 2015

1 Comment

  1. carr

    Some one had made a story and posted it on face book about an orgy and the men were on Prep but one was not. I said on a comment that for added protection you should still use a condom for added protection. Is that comment false as no medication is 100 percent accurate and all body types are not the same as drugs affect people different.


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