Taking the antiviral tenofovir (Viread) once daily can prevent HIV transmission among injection drug users, researchers have found.

Daily tenofovir reduced HIV risk among injection drug users by nearly half compared with placebo, according to Michael Martin, MD, of the CDC, and colleagues.

The phase-3 randomized clinical trial is the latest to show that pre-exposure prophylaxis (PrEP) can protect people at high risk for HIV. Previous studies have shown that either tenofovir alone or in combination with emtricitabine (Emtriva), can reduce the risk for HIV infection in other populations, including men who have sex with men (MSM), heterosexual men and women and heterosexual couples in which one partner has HIV and the other does not.

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“This study completes the picture of PrEP efficacy for all major HIV risk groups,” Martin said in a statement. “We now know that pre-exposure prophylaxis can be a potentially vital option for HIV prevention in people at very high risk for infection, whether through sexual transmission or injection drug use.”

He and colleagues enrolled 2,413 injection drug users from 17 drug-treatment clinics in Bankok, who tested negative for HIV in the previous 12 months, and randomly assigned them one-to-one to either tenofovir or placebo.

Participants were provided with condoms and methadone treatment and were tested monthly for HIV. They also underwent risk-reduction and adherence counseling and blood safety tests every three months. Average follow-up was four years.

Overall, 50 participants became infected with HIV during the study period — 17 in the tenofovir group and 33 in the placebo group (0.35 vs. 0.68 per 100 person years).This equated to a significant 48.9% reduction in HIV incidence among those taking the drug (P=0.01).

Tenofovir was generally safe and well tolerated. Adverse events included nausea and vomiting (8% in the tenofovir group vs. 5% in the placebo group; P=0.002) and grade 1 or 2 elevations in alanine aminotransferase (53% vs. 49%; P=0.003).

The researchers also conducted a substudy among participants in the tenofovir arm to determine how adherence to PrEP influenced efficacy. They found that participants with detectable tenofovir in their blood had a 70% reduced risk for HIV compared with participants with undetectable levels of the drug.

“These results underscore the importance of helping people using pre-exposure prophylaxis achieve effective levels of adherence,” the researchers wrote.

In an accompanying editorial, Salim Abdool Karim, MBChB, PhD, of the University of KwaZulu-Natal in Durban, South Africa, cautioned the study findings do not provide clear evidence that PrEP prevents HIV transmission specifically attributable to needle sharing.

Currently, there is no biological marker to determine whether HIV was transmitted sexually or via needle-sharing, he noted, adding that at least part of the observed reduction in risk in the study was likely due to reduced sexual transmission.

However, Karim acknowledged the results were promising and noted that PrEP should be considered as another option for preventing HIV infection, with other proven tactics such as needle exchanges, safe sex and counseling.


  1. Choopanya K et al. Lancet. 2013; doi: 10.1016/S0140-6736(13)61127-7.
  2. Abdool Karim SS. Lancet. 2013; doi: 10.1016/S0140-6736(13)61140-X.