Neil Canavan

July 11, 2013

KUALA LUMPUR, Malaysia — A large study of intravenous drug users has found a surprisingly high rate of adherence to pre-exposure prophylaxis with tenofovir, resulting in a marked reduction in new HIV infections.

"The study tells us that pre-exposure prophylaxis can work for all populations at risk for HIV, including people who inject drugs," said study investigator Michael Martin, MD, from the Centers for Disease Control and Prevention in Atlanta, Georgia.

Dr. Martin presented findings here at the 7th International AIDS Society (IAS) Conference on HIV Pathogenesis, Treatment and Prevention.

The double-blind placebo-controlled Bangkok Tenofovir Study involved 2413 intravenous drug users. The cohort was 80% male, and the average age was 31 years.

Investigators randomized participants to receive daily oral tenofovir 300 mg or placebo. "We provided monthly HIV testing, participant-centered risk-reduction and adherence counseling, blood safety testing every 3 months, condoms, and methadone treatment," said Dr. Martin.

Participants were asked to record their medication use in an adherence diary or were directly observed taking the study drug. At monthly visits, the staff and the participant reviewed the adherence diary and did a pill count.

Results showed that participants took the drug 84% of the time, which translated into a substantial reduction in the rate of HIV infection. "We had 17 new infections in the tenofovir group and 33 in the placebo group," Dr. Martin reported. "This translates into a 49% reduction in risk (P = .01)."

Adherence did not differ by treatment group (P = .16). However, older participants were more adherent than younger participants (P < .001), and women were more adherent than men (P = .04).

"Needle sharing and sexual risk were similar in the 2 study arms," Dr. Martin explained. However, participants reported that these behaviors declined substantially during the trial. "This was true for both treatment groups."

Despite the positive data that continue to emerge for pre-exposure prophylaxis, real-world use remains limited. Antiretroviral medications for pre-exposure prophylaxis are "not flying off the shelf," Robert Grant, MD, lead investigator of the landmark Pre-Exposure Prophylaxis Initiative (iPrEx) trial, told reporters attending a news conference.

Perceptions From the iPrEx Trial

"We're finding that demand for such services and people interested in providing pre-exposure prophylaxis to their clients remain relatively low. We think that part of this is that it takes time for people to get their heads around new ideas, but part of it is that we really do need to learn more about how best to provide pre-exposure prophylaxis and how best to promote it's effective use."

At the IAS meeting, Dr. Grant reported recent findings from an open-label extension of the iPrEx trial, in which 65% of the original 2340 patients participated. Of the 1451 participants who were not infected with HIV at the time of enrollment in the extension study, 1038 chose to receive pre-exposure prophylaxis.

"We were impressed that 72% of those offered pre-exposure prophylaxis chose to participate, and of those who did, 72% had detectable drug levels," he reported.

That said, it's obvious that pre-exposure prophylaxis is not for everyone, Dr. Grant noted. "It's for people who perceive themselves to be at risk. If roughly half of iPrEx participants are able to appropriately use pre-exposure prophylaxis, that's a substantial number."

Dr. Martin has disclosed no relevant financial relationships. Dr. Grant reports serving as an advisor and consultant for Siemens AG.

The 7th International AIDS Society (IAS) Conference on HIV Pathogenesis, Treatment and Prevention: Abstracts WELBC05 and WELBC02. Presented July 3, 2013.


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