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Arguments supporting pre-exposure prophylaxis (PrEP) have been further bolstered this week, as another study confirms the efficacy of a daily dosage of medication in preventing against HIV transmission.
“Our study adds to the growing body of evidence that PrEP is an incredibly important tool in the fight against HIV,” says Megan Coleman, director of community research at Whitman-Walker Health, who served as the principal investigator on the study.
Known as the PrEP Demo Project, the study examined the real world use of PrEP among men who have sex with men (MSM) and transgender women in three U.S. cities. It analyzed the level of adherence to prescribed medication, the sexual behaviors, and the incidence of STI and HIV infection among 557 MSM and trans women in Washington, San Francisco and Miami. The results of the study, which hold promise for advocates of PrEP, were published in the Journal of the American Medical Association on Monday.
All participants were instructed to take Truvada, an antiretroviral drug used to treat HIV, on a daily basis. They were also provided with support tools, in order to help them remain adherent throughout the course of the 48-week study. These included motivational interviewing, pill boxes to help organize their daily doses, and strategies to help incorporate taking the medication as part of their daily lives.
According to Coleman, cohorts in Washington and San Francisco had an adherence rate of 80 to 86 percent, defined as taking four or more doses per week of Truvada. But a similar cohort in Miami demonstrated a lower level of adherence.
Specifically for Washington, about 40 percent of participants reported taking six or more doses per week, suggesting daily adherence, and another 40 percent took more than four doses, resulting in a level of medication in the blood that not only suggested fairly regular adherence, but provided some significant level of protection against HIV, even if participants were not taking it daily as prescribed.
“For MSM and trans women, Truvada seems to have a longer half-life, and once it reaches a protective level, which takes about seven days, it seems to stay in the body and offer a little bit of forgiveness for missed doses,” she explains. “We don’t see the same results in other studies dealing with women taking Truvada for PrEP. We think they have to take it almost every day to have the same effects.”
Coleman says more research is needed to look into why there appears to be a disparity when it comes to cisgender women, as well as why participants in Miami appeared to have lower levels of adherence than their D.C. and San Francisco counterparts.
Researchers also learned that participants who reported 2 or more condomless anal sex partners in the last three months were more likely to adhere to the medication than those who engaged in less risky sexual behavior. Coleman says this appears to mimic results from other studies on PrEP that indicate those who are more aware of their sexual risk are more likely to incorporate PrEP into their lives.
“Overall, participants who started the medication and were adherent to the medication in the beginning were more likely to remain adherent throughout the year,” she says. “It became part of their routine, and made it more likely they would take at least four doses per week.”
Of course, for those who engage in condomless sex, there is always the risk of contracting other sexually-transmitted infections (STIs). Although the PrEP Demo Project found that STI incidence did not increase over the 48-week period, at any given time about a quarter of participants had some form of STI. According to Coleman, about 8 to 10 percent contracted syphilis, though the bulk of STIs that patients presented with were gonorrhea and chlamydia.
“We had high levels of baseline STI rates: About a quarter of people had an STI at baseline, and it stayed high throughout the study, but didn’t increase over time,” Coleman explains. “So patients were having condomless sex and presented with STIs at their first visit, when they started the medication. Those patients were then treated as part of the study or through their medical provider…. At the end of the study, about a quarter had STIs. So the same person did not have an STI throughout the entire study, but at any given time, about a quarter of people had an STI. But in many cases, those were different individuals.”
Coleman argues that this finding highlights the need for regular STI testing and treatment among people who are on PrEP and regularly report that they engage in condomless sex.
Unlike some other PrEP studies where no participants became HIV-positive, two individuals out of 557 in the PrEP Demo Project did. However, neither had any detectable level of the drug in their blood and neither had evidence of HIV resistance. One was diagnosed as positive 19 weeks into the study, but reported that the last time he had taken the dose was a month prior, and the second who seroconverted had no detectable level of the medication in his blood beginning after the fourth week of the study.
Coleman cautioned that the study had some limitations that indicated a need for further studies looking at other variables. For instance, all participants were provided with Truvada free of charge, so it is unclear what effect financial barriers to accessing PrEP may have on adherence. She also noted that African-Americans and transgender participants were underrepresented in the study, highlighting the need for more dedicated and targeted outreach to those underrepresented groups in future studies.
“I think our study definitely reinforces that the use of PrEP may help prevent HIV infections, and did not increase sexually-transmitted infections, which is a part of naysayers’ argument,” says Coleman. “The fact that adherence was really high in the cohort and HIV incidence was very low, despite the high rate of STIs in the participants, was extremely supportive of the idea of PrEP working in the community and where it fits in the HIV prevention spectrum.”