Emma Hitt, PhD

July 26, 2011

July 26, 2011 (Rome, Italy) — Preexposure prophylaxis (PrEP) with oral emtricitabine/tenofovir (FTC/TDF) appears to prevent the acquisition of HIV infection in men who have sex with men (MSM) who receive other preventive services, according to new findings from the iPrEx study.

Robert Grant, MD, associate professor of medicine at the Gladstone Institute of Virology and Immunology, University of California at San Francisco, presented the "completed observation" findings during a late-breaking session here at the 6th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention.

Findings from the study were previously published in the New England Journal of Medicine (2010;363:2587-2599).

The study, conducted in Brazil, Ecuador, Peru, South Africa, Thailand, and the United States, looked at 2499 MSM, including transgendered individuals who were male at birth. Participants were randomized to receive daily oral FTC/TDF or placebo. All subjects received HIV testing, risk-reduction counseling, condoms, and management of sexually transmitted infections.

After approximately 144 weeks of follow-up, PrEP efficacy was 45% (95% confidence interval, 23% to 61%; P = .0005) in the intent-to-treat analysis. However, when the researchers analyzed data from the group that received FTC/TDF, the protection rate in people who had detectable levels of the drug in their blood was 92%.

Among the infections that developed, there was no evidence of resistance to study drugs and no difference between the study groups in viral load at the time study drugs were discontinued. No difference in efficacy was observed between the 2 groups on the basis of ethnicity, alcohol use, schooling, or age.

Efficacy appeared to be higher among the 59% of participants reporting unprotected receptive anal intercourse (52% vs 25%; P = .04), and was numerically higher in the 13% of participants who had been circumcised, although the difference was not significant (83% vs 36%, P = .10).

Among 366 men (15%) who self-identified as "trans" or who reported using female sex hormones, most had not undergone surgery. In this group, there were 11 infections in the FTC/TDF group and 11 in the placebo group, indicating an efficacy of –4%.

According to Dr. Grant, oral FTC/TDF use was nearly 90% to 100% at some sites, but was considerably lower at other sites.

At each 12-week follow-up study visit, hair samples were collected and questionnaires were completed. "Hair shows promise as a way of monitoring for compliance to treatment," he told Medscape Medical News. "There is no evidence for risk compensation, even among those who thought they were taking FTC/TDF," he added.

Dr. Grant added that differences in PrEP efficacy in trans women might be due to chance, patterns of PrEP use, sexual practices, or hormonal effects on drug transport in the mucosa.

The study was not commercially funded, but the study drug was donated by Gilead. The authors have disclosed no relevant financial relationships.

6th International AIDS Society (IAS) Conference on HIV Pathogenesis, Treatment and Prevention: Abstract WELBC04. Presented July 22, 2011.

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