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Henry J. Kaiser Family Foundation • Medical News
Merck's Antiretroviral Isentress More Efficient in Suppressing HIV Among Untreated Patients

October 28, 2008

Merck's antiretroviral drug Isentress suppresses levels of HIV in previously untreated patients better than the company's antiretroviral efavirenz, according to research presented Sunday at a meeting of the American Society of Microbiology and the Infectious Diseases Society of America, Reuters reports. According to Phase III clinical trial results, Isentress -- known generically as raltegravir -- reduced HIV viral loads to undetectable levels in 86% of patients compared with 82% of patients treated with efavirenz (Fox, Reuters, 10/26).

FDA in October 2007 approved raltegravir for use by HIV-positive people who have not responded to other treatments. Raltegravir works by blocking an HIV enzyme called integrase. Integrase is one of the three enzymes necessary for HIV to replicate in the body, and integrase inhibitors stop HIV from inserting its genes into uninfected DNA (Kaiser Daily HIV/AIDS Report, 10/15/07). The agency also granted Isentress accelerated approval for use among patients who showed initial signs of resistance to existing antiretrovirals. According to Merck, up to 40% of the approximately 500,000 HIV-positive people in the U.S. receiving antiretrovirals have developed resistance to the drugs. In addition, researchers at the conference said that drug-related adverse effects were significantly fewer in patients treated with Isentress (44%) than with efavirenz (77%) (AFP/Yahoo! News, 10/26).

Robin Isaacs, executive director for infectious disease clinical research at Merck, said, "There was a desperate unmet medical need for those patients who had failed other therapies" until recent years. He added that Isentress and Pfizer's Selzentry -- also approved last year -- helped address that need, along with three other new drugs: Boehringer Ingelheim's Aptivus, and Johnson & Johnson's Prezista and Intelence. According to Isaacs, patients "have all these different options now, which they didn't before, to build new successful regimens."

According to AP/Yahoo! Finance, Pfizer at the conference also presented research from a 48-week study comparing its antiretroviral Selzentry with Bristol-Myer Squibb's antiretroviral Sustiva in a total of 417 patients also receiving GlaxoSmithKline's antiretroviral combination drug Combivir. In both groups, 68% of patients had the HIV virus reduced to undetectable levels; however, 4.2% of those who got Selzentry and 14.2% taking Sustiva stopped because of side effects (Johnson, AP/Yahoo! Finance, 10/26).

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