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FDA Panel Recommends Agency Approve Pfizer's Antiretroviral Maraviroc

April 25, 2007

An FDA panel of outside experts on Tuesday unanimously recommended that the agency approve Pfizer's antiretroviral drug maraviroc, the Wall Street Journal reports. Pfizer has proposed using maraviroc to treat people with advanced HIV or AIDS who have not responded to other medications, according to the Journal (Corbett Dooren, Wall Street Journal, 4/25). Maraviroc works by blocking a protein, called CCR5, on human immune system cells that HIV uses as a portal to enter and infect the cell. Pfizer plans to offer the drug with a test developed by Monogram Biosciences that determines if people likely will respond to the treatment. FDA last week ahead of the panel's meeting on Tuesday raised concerns that maraviroc could be associated with an increased risk of liver damage, lymphoma and infections. According to FDA, other CCR5 inhibitors under development have been shown to increase safety risk issues. Pfizer said its studies have shown that maraviroc has no significant effect on the heart and did not increase the incidence of liver problems, cancer or infection compared with other HIV/AIDS drugs. Although FDA "continues to be concerned about potential safety issues with the entire class of drugs," some agency reviewers have noted no increases in lymphomas or infections among people taking maraviroc. FDA reviewers have noted a "modest" increase in liver problems among people taking the drug. Pfizer has proposed selling maraviroc under the brand name Celsentri (Kaiser Daily HIV/AIDS Report, 4/23). The 12-member FDA panel said that post approval studies should look for blood cancers and heart and liver problems. According to the Journal, some panel members said they are concerned that maraviroc studies have been conducted primarily among white men (Wall Street Journal, 4/25). The panel recommended that Pfizer conduct studies of maraviroc's interaction with other drugs and its effects on women and minorities, the AP/South Florida Sun-Sentinel reports. The panel also expressed concern that maraviroc could accelerate HIV mutations. According to the AP/Sun-Sentinel, people taking maraviroc likely would need to be monitored to ensure the drug is not accelerating mutations (AP/South Florida Sun-Sentinel, 4/25). In two primary clinical trials conducted among more than 1,000 participants, maraviroc was found to decrease viral loads to undetectable levels in 45% of participants after 24 weeks, compared with 23% of those who did not take maraviroc, the Journal reports. Pfizer has said it will continue studies of maraviroc for five years after approval. FDA likely will complete its evaluation of maraviroc by the end of June, according to Katie Laessing, a team leader in FDA's antiviral products division (Wall Street Journal, 4/25).

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