U.S. review backs Pfizer AIDS drug

An experimental Pfizer Inc. AIDS pill was effective at suppressing the HIV virus when added to the best available drug regimens, U.S. drug reviewers said in an analysis released Friday.

The Food and Drug Administration staff, however, said they would ask an advisory panel that meets Tuesday for advice “regarding the possible need for special labeling as well as whether additional clinical trials should be performed to address particular safety issues.”

The drug, called maraviroc, could be the first drug on the market that blocks the CCR5 co-receptor that serves as a main entryway for the virus into cells.

Analysts have projected maraviroc sales at about $500 million in 2011 if it is approved.

AIDS experts say new types of drugs are needed for patients who become resistant to older treatments.

But the CCR5 inhibitors have raised safety concerns. Earlier medicines under development were associated with risks such as lymphoma and liver damage.

Maraviroc did not increase lymphoma in Pfizer studies but there appeared to be a modest increase in liver-related abnormalities, the FDA reviewers said.

Animal studies showed maraviroc had the potential to prolong the “QT interval,” the time it takes the heart to electrically recharge itself, the FDA staff said. Extended QT intervals can lead to heart problems.

New York-based Pfizer, in a separate summary, said studies did not find any meaningful QT difference in people.

The FDA reviewers said their analyses of the drug’s effectiveness were consistent with Pfizer’s. The company’s studies showed the HIV virus was suppressed in about 45% of patients who took maraviroc for 24 weeks, compared with 23% of patients who got a placebo. All patients also were treated with a cocktail of the best available drugs.

An FDA advisory panel of outside experts is set to vote Tuesday on whether to back approval for maraviroc for patients already treated with other drugs. The agency will make the final decision but usually follows panel recommendations.

Jacob Lalezari, the lead researcher for the U.S. portion of Pfizer’s trials, said AIDS patients who were running out of options had responded well to the drug.

But he added that “you don’t know about five- or 10-year safety issues until a drug’s been out five or 10 years.”

Pfizer shares fell 10 cents to $26.97.