Does PrEP Work the Same for Men and Women?
Updated January 05, 2015.
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From a clinical standpoint, the evidence is clear: if taken correctly and with good levels of adherence, HIV pre-exposure prophylaxis (PrEP) can reduce the risk of acquiring HIV by up to 92%. But the fact is, clinical studies don’t necessarily hold up as well in the real world, particularly over the long term and/or among different at-risk populations.
A recent study conducted by Angela Kashuba of the University of North Carolina and colleagues now suggests that PrEP—in the form of a once-daily dose of Truvada (tenofovir + emtricitabine)—may requires far greater adherence levels in women than in men.
How the Study Was Designed
In order to quantify this, Kashuba and her team first calculated what amount of Truvada would be needed in order to achieve the complete suppression of HIV on target mucosal tissues.
Next, using data from an earlier study exploring the absorption/distribution of Truvada in vaginal, cervical and rectal tissues, they created a mathematical model to determine the drug concentration levels that would be attained given dosages of between two to seven doses per week.
In doing so, the researchers were able to determine that:
- Two doses of Truvada per week may, in fact, be enough to maintain the target concentrations within rectal tissues across all population groups.
- But that a daily dose of Truvada would likely be needed in order to achieve the same results in vaginal and cervical tissues, and then only in 75% of women.
The researchers explained that Truvada was not only found in higher concentration in rectal tissue, but that the DNA molecules with which they compete were far lower than in vaginal or cervical tissues.
Results May Better Explain Recent PrEP Trial Failures
These study help shed some light as both the VOICE and FEM-PrEP studies—which examine PrEP usage in women—failed after participants achieved adherence levels of only 29% and 36%, respectively. By contrast, an extension of the I-PrEX OLE study in 2014 showed that PrEP was 100% effective in men who have sex with men (MSM) even with three missed doses per week.
Whether these findings will affect the rollout of PrEP among at-risk women is largely unknown given that the Centers for Disease Control and Prevention (CDC) already recommends the daily dosing of Truvada for all PrEP users.
What it will likely reinforce, however, is that PrEP is not a stand-alone tool but rather one to be used in conjunction with other safer sex practices (including condoms and antiretroviral therapy for the HIV-infected partner).
PrEP As a "Day-Before-Morning-After" Pill?
Meanwhile, another study from ANRS (France's national research agency) has shown that taking a single dose of Truvada before sex and a daily pill for two days after may provide ample protection from HIV in MSM.
The double-blind, 400-participant trial was conducted in six French cities and Montreal from February 2012 and was seen to be so successful as to lead investigators to "unblind" the study and switch all placebo users to Truvada. While the full data won't be available until 2015, it does further highlight the efficacy of the drug in non-infected MSM when compared to women.
However, not everyone is pleased with to promote the "day-before-morning after" regimen, suggesting that it both promotes Truvada as a party drug and increases the likelihood of high-risk, condom-less sex. Among the most vocal opponents is Michael Weinstein, the oft-outspoken president of the AIDS Healthcare Foundation (AHF). In early November 2014, Weinstein and his colleagues took out ads in national gay publications questioning the use of PrEP as public health policy under the headline "What if you’re wrong about PrEP?”
It’s a debate that will likely continue as we move from the controlled environment of clinical trials to the real-world observations in key populations.
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Sources:
Cottrell, M.; Yang, K.; Prince, H.; et al. "Predicting effective Truvada PrEP dosing strategies with a novel PK–PD model incorporating tissue active metabolites and endogenous nucleotides (EN)." HIV Research for Prevention Conference. 28-31 October, 2014; Cape Town, South Africa; oral abstract 22.06 LB.
Microbicides Trial Network (MTN). "MTN Statement on Decision to Discontinue Use of Oral Tenofovir Tablets in VOICE, a Major HIV Prevention Study in Women." Press release issued September 28, 2011.
National Institute of Allergies and Infectious Diseases (NIAID). "The FEM-PrEP HIV Prevention Study and Its Implications for NIAID Research." Bethesda, Maryland; press release issued April 18, 2011.
Grant, R.; Lama, J.; Anderson, P.; et al. "Preexposure Chemoprophylaxis for HIV Prevention in Men Who Have Sex with Men."New England Journal of Medicine. December 30, 2010; 363(27):2587-2599.
Agence National de Recherche sur le Sida et Les Hépatites Virales (ANRS). "Un grand succes dans la lutte contre le vih/sida [A major success in the fight against HIV/AIDS]." Press release issued October 29, 2014.
The New York Times. "AIDS Group Wages Lonely War Against Pill to Prevent H.I.V." Published November 16, 2014.
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