A fixed-dose daily treatment of the antiviral drugs emtricitabine and tenofovir - marketed together as Truvada - was first approved in 2002.
Pre-exposure prophylaxis (PrEP) is a form of treatment whereby a fixed-dose of antiviral drugs are prescribed and combined with safer sex practices for people identified to be at high risk for HIV infection.
If an individual is exposed to HIV through intravenous drug use or risky sexual activity, PrEP - commercially available as the drug Truvada - can prevent permanent infection.
"Our study is the first to extend the understanding of the use of PrEP in a real-world setting and suggests that the treatment may prevent new HIV infections even in a high-risk setting," explains lead author Dr. Jonathan Volk.
PrEP was first approved for use by the US Food and Drug Administration (FDA) in 2012. Until now, however, evidence supporting its efficacy had only come from clinical trials and a demonstration project, despite a dramatic increase in referrals for and initiation of the treatment since its approval.
Earlier this year, Medical News Today reported on one such trial - a study that found the treatment reduced the risk of HIV infection in men who have sex with men by 86%.
For the new study, published in Clinical Infectious Diseases, researchers from Kaiser Permanente examined referrals and courses of PrEP initiated at the San Francisco Medical Center over a period of 32 months. During this time, there was a total of 1,045 referrals and 657 patients who commenced PrEP.
The average age of these patients was 37 and 99% were men who have sex with men. In comparison with patients who did not initiate courses of PrEP, patients who did were more likely to report having multiple sexual partners and less likely to report having a sexual partner infected with HIV.
High rates of STIs were observed, but no new cases of HIV
To assess how PrEP use affected sexual behaviors, the researchers surveyed 143 of the patients about behavior following 6 months of the treatment. They found that many sexual behaviors remained unchanged; 74% reported that their number of sexual partners had not changed and 56% reported that their condom use was unchanged.
In comparison, the number of sexual partners decreased in 15% of the patients and increased in 11%. Condom use decreased in 41% of patients and only increased in 3%.
There were also a large number of sexually transmitted infections (STIs) among the patients using PrEP. After 6 months from beginning the treatment, 30% had been diagnosed with at least one STI, and this figure rose to 50% after 12 months.
- An estimated 1,218,400 people aged 13 years and above live with HIV in the US
- Around 1 in 8 of these are unaware of their infection
- HIV can be transmitted through sexual contact, using contaminated hypodermic needles, during pregnancy and through breastfeeding.
Despite these high rates of STIs, however, the researchers conclude that there were no new HIV infections in this population.
"Without a control group, we don't know if these STI rates were higher than what we would have seen without PrEP," acknowledges co-author Julia Marcus, a postdoctoral fellow at the Kaiser Permanente Division of Research. "Ongoing screening and treatments for STIs, including hepatitis C, are an essential component of a PrEP treatment program."
Senior author Dr. Bradley Hare, director of HIV Care and Prevention at Kaiser Permanente San Francisco, states that as well as ongoing STI screening, patients using PrEP should also be closely monitored for any side effects of Truvada and changes in kidney function.
Additionally, while the majority of patients assessed in the study were men who have sex with men, this group is just one of several who are at risk for HIV. The researchers state that there is a need for outreach to others at risk, including transgender women, heterosexual men and women and the users of intravenous drugs.
Previously, Medical News Today reported on research that describes two novel approaches that could prevent HIV infection by targeting proteins in semen known to boost HIV transmission.