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Key Hearing Awaits Pfizer Drug

A panel of medical experts is meeting Tuesday to evaluate an HIV and AIDS treatment.

A panel of outside medical experts is meeting Tuesday to evaluate a


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HIV and AIDS drug that, if approved, would the the first in a new class of treatments.

Pfizer is seeking support from the Food and Drug Administration for maraviroc, a pill being targeted at patients for whom other drugs, or drug combinations, have become ineffective.

Maraviroc "could broaden the arsenal of treatments to combat resistant forms" of the virus that causes AIDS, Pfizer told analysts last week when it issued first-quarter results. Maraviroc would be the first new oral class of HIV, or human immunodeficiency virus, medicines in more than 10 years, Pfizer said.

The FDA advisory panel must decide if Pfizer has proven that its drug can avoid the setbacks found in other compounds in this class, known as CCR5 antagonists.


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halted work in October 2005 after its drug caused liver damage. The compound was in the third and final stage of clinical trials.

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In August 2006,



said it was initiating a new phase II trial of its product because five patients in an earlier study developed different types of cancer. The company said it couldn't tell from the earlier trial if there was a link between its drug and the cancers.

So far, it appears that Pfizer's drug hasn't experienced the types of side effects that affected other CCR5 drugs, said an FDA staff report issued Friday. The FDA noted a "modest increase" in liver-related side effects. The data are being analyzed to determine if side effects were caused by Pfizer's drug, alcohol, another AIDS drug or viral hepatitis.

Pfizer's clinical trials have met their goals of reducing the amount of detectable virus in the blood when maraviroc is added to standard AIDS treatments, the staff report said. Although the FDA isn't bound by its advisory panels' recommendations, it usually follows them.

FDA researchers routinely issue analyses before advisory committee meetings. The FDA staff often recommends questions for panel members to ask company representatives.

For example, the staff wants to know if problems with other CCR5 antagonists might show up once maraviroc reaches the market and is given to many more people than were tested during trials.

The staff says Pfizer should comment on the drug's potential effectiveness for women and Aftrican-Americans since 90% of patients in the two key clinical trials were men and 83% were Caucasian. FDA researchers say Pfizer should outline plans for post-marketing surveillance or extra studies "to further characterize the safety and efficacy profile" of maraviroc.

The Pfizer drug has been in development for 10 years. Pfizer says maraviroc is different than other medications because it blocks the AIDS virus from entering human cells rather than trying to fight the virus inside white blood cells.

The drug is called a CCR5 antagonist because it blocks the AIDS virus from entering cells through the most common point of attack, called a CCR5 coreceptor.