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Merck to Offer Experimental Integrase Inhibitor in Worldwide Expanded Access Program

August 18, 2006

Drug company Merck on Thursday at the XVI International AIDS Conference in Toronto announced that it will expand access to its experimental integrase inhibitor antiretroviral drug -- which might control HIV more effectively in some HIV-positive people than other common drugs on the market -- beyond clinical trial participants, the Wall Street Journal reports (Chase, Wall Street Journal, 8/18). Integrase is one of the three enzymes necessary for HIV to replicate in the body, and integrase inhibitors would stop HIV from inserting its genes into uninfected DNA. The other two enzymes necessary for viral replication -- reverse transcriptase and protease -- already are targeted by a variety of antiretroviral drugs. The decision to expand access to the drug, known as MK-0518, comes after a 24-week study that finds 90% of the HIV-positive people in the trial who took 100 milligrams to 600 milligrams of the drug in combination with tenofovir and lamivudine twice daily reduced HIV viral loads to undetectable levels. Most of the viral load reduction took place in the first four to eight weeks of taking the drug, Robin Isaacs, Merck's director of clinical research who was involved with the study, said. He added that the MK-0518 combination in all doses reduced the viral load faster than the control group, which was taking tenofovir, lamivudine and efavirenz (Kaiser Daily HIV/AIDS Report, 8/14). The expanded access program allows the company to provide the drug internationally to HIV-positive people resistant to current antiretrovirals and is supported by regulatory agencies, the Newark Star-Ledger reports. To be eligible for the program, recipients of the drug must be ages 16 or older, living with HIV-1, clinically stable and have limited or no other treatment options. "Making MK-0518 available to those who would like access to this investigational drug but who are unable to participate in the clinical studies underscores our commitment to patients," Peter Kim, president of Merck Research Laboratories, said at the conference (MacPherson, Newark Star-Ledger, 8/17). Merck will begin enrolling people in the expanded access program in the next few months (Drug Industry Daily, 8/18). The company also plans to begin Phase III clinical trials, which are expected to involve 700 people. Martin Markowitz, a lead investigator of the Merck data, said it is unclear when the drug will be available. The drug must be put through several more years of testing before FDA can review it (Kaiser Daily HIV/AIDS Report, 8/14).

CCR5 Blockers
At the conference, Schering-Plough and Pfizer also reported early data on their experimental drugs, vicriviroc and maraviroc, respectively. In the Schering-Plough study, people taking vicriviroc experienced more "durable drops" in HIV viral levels and rises in CD4+ T cells, compared with a group of people taking a placebo. Five of 90 people taking vicriviroc developed cancer during the study, compared with two of 28 people in the placebo group, which raises concerns about the treatment's link to malignancy, the Journal reports. The treatment is in a class known as CCR5 blockers, which are known only to block one type of HIV, the R5 virus, which occurs early on in the course of infection. CCR5 blockers do not attack the X4 virus, a more aggressive virus that occurs later in the infection cycle. Pfizer at the conference reported results of its CCR5 blocker, maraviroc, which when combined with a standard antiretroviral treatment regimen did not prove to be any better in suppressing HIV than a placebo plus the standard regimen (Wall Street Journal, 8/18). is serving as the official webcaster of the conference. View the guide to coverage and all webcasts, interviews and a daily video round up of conference highlights at

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