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FDA Panel Backs HIV Drug, Wall St Jnl
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Pfizer Treatment Blocks Pathway Used to Infect Cells
Wall St Jnl
By JENNIFER CORBETT DOOREN
April 25, 2007; Page A4
WASHINGTON -- A Food and Drug Administration panel of outside medical experts unanimously recommended the agency approve a new type of drug by Pfizer Inc. to treat HIV infection.
The drug, known by its generic name as maraviroc, would be the first drug to block a pathway that HIV uses to infect cells. Maraviroc interferes with a receptor on the surface of cells, called CCR5, to prevent HIV from entering cells. In some patients, however, HIV uses another receptor known as CXCR4 to enter cells, which would thwart maraviroc. HIV is the virus that causes AIDS.
Katie Laessig, a team leader in the FDA's antiviral-products division, said the agency was at the end of the fourth month in the drug's review, suggesting the agency will complete its evaluation by the end of June. Maraviroc was granted priority review status by the FDA, which reduces the time the agency takes to consider a new medicine. The designation is reserved for treatments the agency deems a likely advance over existing drugs. Pfizer has proposed the brand name Celsentri for the drug.
The FDA usually follows the advice of its panels but isn't required to do so. Howard Mayer, Pfizer's global clinical leader for the drug, said he was "extremely pleased" about the panel's vote.
Pfizer has proposed using maraviroc in patients with advanced HIV infection or AIDS who have failed treatment with other drugs, which is estimated at about 40,000 patients in the U.S. Patients would also likely have to undergo testing to see whether their type of HIV exploits the CCR5 pathway. One firm, Monogram Biosciences Inc. of South San Francisco, makes such a test. About one million Americans are infected with HIV, according to the Centers for Disease Control and Prevention.
While the 12-member panel backed the drug because new HIV treatments are needed, many of the experts said they shared safety concerns raised by the FDA. Patients with HIV are typically treated with a "cocktail" of two or three drugs. Over time, most HIV viruses mutate and become less vulnerable to those drugs.
The agency said it was concerned about possible liver damage, heart problems and infection among patients taking the maraviroc, and noted that GlaxoSmithKline PLC stopped working on a rival CCR5 drug after it was found to cause liver problems.
The FDA said clinical studies involving maraviroc showed a possible "modest increase in liver-related side effects" among patients who received the drug. The agency also said there was a "potential" for the drug to disturb heart rhythms, an effect called QT prolongation that can lead to heart problems.
Because drugs like maraviroc block a cell receptor that is involved with the body's immune system, the agency said there is a potential for such drugs to raise the risk of infection, lymphoma and other blood cancers. So far those risks haven't been seen with maraviroc.
The panel said postapproval studies should look for blood cancers, along with heart and liver problems. Many panel members also were concerned that maraviroc was studied in a predominantly white, male population. Pfizer has proposed to study maraviroc for five years after the drug is approved.
Maraviroc was studied in two main clinical trials that involved more than 1,000 patients. All of the patients received current HIV drugs, and about 800 also received maraviroc. Overall, the studies showed that about 45% of patients receiving maraviroc had their HIV suppressed to undetectable levels compared with 23% who didn't receive maraviroc after 24 weeks on treatment.
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