HIV: Preexposure Prophylaxis May Not Increase Risky Behavior

Laurie Barclay, MD

October 18, 2013

HIV-negative partners in heterosexual serodiscordant couples who were taking oral, tenofovir-based prophylaxis against HIV transmission did not report increased high-risk sexual behavior after they knew the drugs were effective, according to a longitudinal analysis of data from the Pre-Exposure Prophylaxis to Prevent HIV-1 Acquisition Within HIV-1 Discordant Couples (PartnersPrEP) study.

The analysis was published online October 17 in the Lancet Infectious Diseases.

"Evidence for the effectiveness of new HIV prevention strategies, including pre-exposure prophylaxis, has spurred optimism that the global HIV epidemic might be reversed," senior author Jared M. Baeten, MD, from the University of Washington, Seattle, said in a news release. "However, an important question is whether HIV-negative partners who know they're protected by prophylaxis will compensate for this by increasing their sexual risk-taking, such as through increasing their levels of unprotected sex."

The Partners PrEP study was a double-blind, randomized, placebo-controlled trial of daily preexposure prophylaxis among 3163 HIV-uninfected partners of heterosexual HIV-serodiscordant couples who were at least 18 years of age. All study participants also received risk-reduction counseling, safety monitoring, pregnancy testing, and tests for gonorrhoea, chlamydia, and trichomoniasis.

The study showed that prophylaxis was effective for HIV prevention. After the efficacy results were reported in July 2011, participants continued monthly follow-up. Regression analyses allowed comparison of the frequency of unprotected sex (without condom use) during the 12 months before and after July 2011 (56,132 person-months from 3024 HIV-uninfected African individuals, 64% of whom were men).

Before July 2011, the average frequency of unprotected sex with the HIV-infected study partner was 59 per 100 person-months compared with 53 after July 2011. This was not a significant change, either immediately (P = .66) or over time (P = .25).

In addition, before July 2011, the researchers had seen a gradual decrease in the frequency of unprotected sex, which they attributed to efficacy of risk counseling and other nonpharmacologic measures. This trend persisted after July 2011.

There was, however, a small but significant increase in unprotected sex with outside partners after July 2011 (average unprotected sex acts per year, 6.8 vs 6.2 acts in a predicted counterfactual scenario if patients had remained unaware of prophylaxis efficacy; P = .04). There was no significant increase in new sexually transmitted infections or pregnancy from before or after July 2011.

"To our knowledge, this study provides the first empirical data on sexual behaviour in heterosexual people receiving open-label oral pre-exposure prophylaxis for HIV prevention," Dr. Baeten said in the release. "The results provide encouraging evidence that behavioural changes as a result of pre-exposure prophylaxis might not undermine its strong HIV prevention and public health benefits."

Limitations of this study include the outcome of self-reported sexual behavior, which is prone to reporting bias, and the assumption of constant frequency and linear trend of sex acts in each segment. Participants were African couples experienced in research who received regular reinforcement of risk-reduction messages and who had completed a median of 23 months of follow-up before unmasking.

In an accompanying comment, Kristen Underhill, JD, PhD, from the Yale Center for Interdisciplinary Research on AIDS, Yale Law School, New Haven, Connecticut, and Kenneth Mayer, MD, from Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, call this analysis "an important advance."

"Future research should examine the behaviours of pre-exposure prophylaxis users outside trial settings, behavioural strategies for optimisation of pre-exposure prophylaxis uptake and adherence while decreasing risk-taking, methods for assessment of users' behaviours over time, and methods for training providers," they write. "Researchers and implementers should also investigate the context of behaviour among pre-exposure prophylaxis users; individuals might have personally meaningful reasons to take risks, such as fertility desires, and understanding these motivations can strengthen efforts to support pre-exposure prophylaxis users before, during, and after use."

The Bill & Melinda Gates Foundation and the US National Institute of Mental Health funded this study. The authors and Dr. Underhill have disclosed no relevant financial relationships. Dr. Mayer has received unrestricted research and educational grants from Gilead.

Lancet Infect Dis. Published online October 17, 2013. Article abstract, Comment extract


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