Daily tablets of the anti-retroviral drug tenofovir disoproxil fumarate reduced HIV incidence by nearly half compared with placebo, according to what was described as the first trial to assess whether preventive treatment with HIV drugs could affect infection rates in people who inject drugs.
For a study to be published on the website of The Lancet, researchers recruited more than 2,400 participants at 17 drug treatment clinics in Bangkok. About half the participants were assigned a daily oral dose of tenofovir and half were assigned placebo. All trial participants were offered monthly HIV testing and risk-reduction counseling and services, plus access to drug rehabilitation treatment.
Participants were followed for an average of four years. Overall, 17 participants in the tenofovir group became infected with HIV, compared with 33 in the placebo group, indicating a reduction in HIV risk of 48.9%. Further analyses of the results showed that the protective effect of the antivirals was best when participants adhered closely to the prescribing regime.
Previous studies have established that pre-exposure prophylaxis effectively reduces sexual transmission of HIV in both heterosexual couples and men who have sex with men, and mother-to-child transmission of HIV. However, this study is said to be the first to show the approach also is effective among people who inject drugs.
This study completes the picture of PrEP efficacy for all major risk groups, Michael Martin, MD, MPH, one of the lead investigators of the study and chief of clinical research for the Thailand Ministry of Public Health-CDC Collaboration, said in a news release. We now know that pre-exposure prophylaxis can be a potentially vital option for HIV prevention in people at very high risk of infection, whether through sexual transmission or injecting drug use.
Adherence was a key factor determining efficacy in our trial among people who inject drugs as it has been in previous PrEP trials examining sexual transmission. These results underscore the importance of helping people using pre-exposure prophylaxis achieve effective levels of adherence.
In a related commentary, Salim Karim, a professor and director of the Center for the AIDS Programme of Research in South Africa at the University of KwaZulu-Natal, noted the reduction in HIV infections may not be specifically attributable to a protective effect of the antivirals on people who become infected through injecting drugs. Some injecting drug users engage in risky sexual behavior, such as selling sex to fund their drug habit, so the protective effect observed in the trial may be at least partially attributable to the established effects of PrEP on sexual transmission of HIV.
Even though questions remain about the extent to which PrEP can be effective in preventing either of the routes of transmission in this group, the overall result is that daily tenofovir does reduce HIV transmission in the injecting drug users.
The introduction of PrEP for HIV prevention in injecting drug users should be considered as an additional component to accompany other proven prevention strategies like needle exchange programs, methadone programs, promotion of safer sex and injecting practices, condoms and HIV counseling and testing.