HIV Drugs Can Prevent Infection
by Bob Roehr
Originally printed 11/25/2010 (Issue 1847 - Between The Lines News)
HIV drugs can do a remarkable job of suppressing high viral loads to undetectable levels, but can they prevent that infection in the first place? Most people thought they could in theory, but there was no proof of that...until now.
A study published in the New England Journal of Medicine on Nov. 23, reported the results from the Preexposure Prophylaxis Initiative (iPrEx) Trial, which found that drugs could reduce new infections by 43.8 percent in high-risk men who have sex with men (MSM) and transgender persons.
"These results represent a major advance in HIV prevention research. For the first time, we have evidence that a daily pill used to treat HIV is partially effective for preventing HIV among gay and bisexual men at high risk for infection, when combined with other prevention strategies. Given the heavy burden of HIV among gay and bisexual men, a new tool with potential additive benefit is exciting and welcome news," said Dr. Kevin Fenton, M.D., Director, CDC National Center for HIV/AIDS, Viral Hepatitis, STD & TB Prevention.
The $43.6 million trial enrolled 2,499 participants at 11 sites on four continents, including San Francisco and Boston. Despite the fact that MSMs are much more likely to be infected with HIV - they are more than half of those infected in the U.S., and in the broader epidemic of sub-Saharan Africa they are at least four times as likely as their heterosexual counterparts to be infected with the virus. This is the first large biochemical prevention study conducted in the MSM population.
Participants were randomized to receive a once a day dose of either Truvada, a single pill containing the drugs emtricitabine and tenofovir, or a placebo - essentially a sugar pill with no active ingredients. They also received counseling on HIV prevention at every meeting with the study team. The analysis was based on a median of 1.2 years on the drug.
Of the first 100 people to become infected with HIV, 64 were receiving placebo (an annual infection rate of about 4 percent) and 36 were on Truvada. The 43.8 percent rate of protection was no home run, but within the same ballpark as the protection seen in other recent prevention trials; the vaginal microbicide trial of tenofovir gel in African women (39 percent) and a vaccine trial in Thailand (31 percent).
Digging deeper, the researchers found that adherence was a very important part of the equation. The men who took at least half of their doses had 50.2 percent fewer infections; those who took at least 90 percent of their medication had 72.8 percent fewer infections. Even the best drugs will not work if people don't take them as prescribed.
Robert Grant, MD, a researcher at the Gladstone Institute at the University of California San Francisco is the principle investigator of the study. He said they asked participants to report how often they took their pills, but because people often are "optimistic" in their recall, and sometimes report what they think researchers want to hear, the study also tested for levels of the drug in the blood of those who became infected.
"No drug was detected in 91 percent; the other 9 percent had detectible levels inside blood cells that were very low. The absence of the drug in the blood is probably due to people not taking it, which could explain all of the infections that did occur" in that group, Grant said.
The association between adherence and the level of protection was similar to what was seen in the microbicides trial. People who most closely used the product as intended had the best results. Cutting corners gave HIV an opportunity that it quickly exploited.
"The iPrEx study results are extremely important and provide strong evidence that PrEP [preexposure prophylaxis] can reduce HIV acquisition among a segment of society disproportionately affected by HIV/AIDS," said Anthony Fauci, MD, director of the NIH National Institute of Allergy and Infectious Diseases which provided $27.8 million toward the study.
He emphasized that despite this good news, "correct and consistent use of condoms and a reduction in the number of sex partners still remain the most effective ways to protect yourself from HIV infection."
"It's critically important to determine how this data holds up in the real world." Says Phill Wilson, President and CEO of the Black AIDS Institute. "We need to see the results of more trials and we need funding for demonstration projects. Also, how do we create environments where we can increase adherence to PrEP? And, during a global recession when many nations, including our own, are cutting back on HIV/AIDS funding, how do we advocate for PrEP funding but maintain our commitment to treatment, especially the expensive but life-saving antiretroviral regimens?"
"This is a very important study." Says Wilson. "But don't break open the champagne yet until we see what happens in the real world."
Gilead Sciences manufactures Truvada and supported the iPrEx study by providing all of the drugs used. The company said it "will be working with the appropriate regulatory agencies to determine if data from this study warrants inclusion in the prescribing information for Truvada."
While doctors can prescribe drugs for "off label" use that the FDA has not approved, and some already prescribe Truvada for prevention, health insurance companies generally only reimburse for the use indicated on the label of the drug.
Adding a prevention indication to the drug label likely will require additional trials in MSM and other populations, particularly with regard to preventing vaginal transmission of HIV. Some of those studies are already underway.
"The big conundrum right now is what does it mean for practice?" Coates said the response was not sufficiently great to signal immediate widespread adoption of this approach as a prevention intervention, particularly given issues of cost.
The retail price of the drug in the U.S. is about $14,000 a year. The NIH pharmacy purchases it for about $5,000 a year Fauci said.
In developing countries, generic versions of Truvada can be purchased for as little as 40 cents a day, according to Grant. However, those are the same places where more than half of the people already infected with HIV - who meet guidelines to begin treatment - cannot do so because of the cost. It is unlikely that public health officials will devote scarce resources to Truvada when a condom will do the same job more cheaply.
Furthermore, an international survey of more than 5,000 participants, to be released next week by the Global Forum on MSM & HIV, found that more than half of MSM worldwide do not have access to basic HIV prevention and treatment services. Adding PrEP to the mix will be a challenge.
The paper "Preexposure Chemoprophylaxis for HIV Prevention in Men Who Have Sex with Men" is freely available from the New England Journal of Medicine at http://www.nejm.org/doi/full/10.1056/NEJMoa1011205
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