In July 2012, the Food and Drug Administration (FDA) approved Truvada, the first and only drug intended to prevent HIV infection. Now, a new study provides more proof that regular use of Truvada (emtricitabine and tenofovir disoproxil fumarate) can reduce an individual’s risk of contracting HIV by more than 90 percent. Importantly, the researchers also found that use of the pill does not equate to an increase in risky sexual behavior.

"We not only gathered behavioral data, but we also tested each participant for both HIV and syphilis — allowing us to map over time how reported changes in overall behavior correlated with actual changes in infection rates," Robert Grant, M.D., professor at University of California, San Francisco, stated in a press release. His research, conducted with colleagues from Gladstone Institutes, a biomedical-research organization affiliated with UCSF, appears online in the journal PLOS ONE.

Pre-exposure Prophylaxis

The story of Truvada as a prophylactic began in July 2007 when a global study, known as iPrEx, began enrollment to test whether this FDA-approved antiretroviral drug, which is manufactured by Gilead Sciences and had been used for years to treat HIV-positive patients over the age of 12, could also prevent new infections. When used for pre-exposure prophylaxis (PrEP), Truvada, as directed by the FDA, was to be taken daily in combination with safer sex practices to reduce the risk of sexually-acquired HIV infection.

A multi-year study, iPrEx enrolled nearly 2,500 men and transgendered women at risk for HIV infection in Peru, Ecuador, South Africa, Brazil, Thailand, and the U.S. Half of the participants were given Truvada, while the other half were given a placebo, none of the participants knowing which they had received. In 2010, the iPrEx trial was hailed as a success when results showed Truvada was effective in reducing the risk of HIV infection by 42 percent compared with placebo in this population. Similarly, in the Partners PrEP trial, which was conducted concurrently among 4,758 heterosexual couples where one partner was HIV-infected and the other was not, Truvada was shown to reduce the risk of HIV infection by 75 percent compared with placebo.

Yet, questions remained as to the drug's real-world effectiveness. In particular, researchers wondered whether people taking the drug might acquire so called “risk compensation” behavior, in which they adjust their actions in response to a change in their perception of risk — for example, people who have applied sunscreen might increase their exposure to the sun beyond their usual amount. Over the course of the iPrEx study, all participants had been asked whether they believed they were receiving Truvada and whether they thought it was working. Study participants were also asked about their behaviors and the researchers observed a decrease in self-reported high risk sexual behavior. Wanting to examine the effects of using Truvada as PrEP more closely, Grant and his colleagues knew they had no real idea as to the truth of participants’ self-reports of sexual behavior. So they decided to study the biological markers of behavior.

“If risk compensation were occurring, those who believed they were receiving Truvada and that it was effective would be more likely to increase their sexual risk behavior," Julia Marcus, Ph.D., the paper's first author, explained. "However, our results revealed the opposite: rates of both HIV and syphilis infections went down, and there was no increase in sexual risk behavior."  In fact, the 2012 follow-up study found that regular use of Truvada reduced risk of HIV infection by more than 90 percent.

“The research team's findings should help to minimize reluctance to embrace Truvada over fears that it could actually lead to increased risk and more infections,” Jeffrey Crowley, Georgetown University and former director of the White House Office of National AIDS Policy, stated in a press release.

 

Source: Grant R, Marcus J, MacMahan V, et al. No link between HIV-prevention pill Truvada and increased sexual risk behavior. PLOS ONE. 2013.