The Food and Drug Administration's panel of virus experts voted 10-4 in favor of the new use, despite some inconsistency in company studies of the drug. Selzentry is approved as a secondary option for HIV patients who are not responding to other antiviral drugs. New York-based Pfizer is asking the FDA to approve the drug as an initial treatment.
Pfizer's initial study comparing Selzentry with Bristol-Myers Squibb's Sustiva failed to meet the goal of showing it was at least as effective at suppressing HIV.
But when Pfizer reanalyzed the results using a different test to screen patients, the study met its goal.
FDA reviewers raised concerns about higher levels of viral activity in patients taking Selzentry compared with Sustiva. About 32 percent of patients did not adequately respond to Pfizer's drug, compared with 24 percent of patients taking the alternative.
A majority of panelists ultimately said the drug works and should be made available as an option for patients, though they expressed lingering concerns about the strength of its effect.
"It's clearly an active drug, it demonstrated effectiveness," said Dr. Russell Van Dyke, of the Tulane University School of Medicine. "But I'm worried it's not as potent as we might like."
Other panelists said they were not comfortable backing a product that could be inferior to drugs already on the market.
"There's a lot that's promising about this drug, but this trial doesn't convince me," said Dr. Barbara McGovern, of Tufts University Medical School.
Panelists said Pfizer should continue collecting data on the drug's effectiveness, particularly in minority populations.
While the FDA is not permitted to consider cost when deciding whether to approve a drug, several panelists commented on Selzentry's high price tag.
If approved, Selzentry would be the most expensive first-line HIV treatment on the U.S. market, according to the AIDS Healthcare Foundation, a nonprofit patient advocacy group. Selzentry's wholesale price per year is over $12,500, according to the group, compared with $4,800 for Bristol-Myers' Sustiva.
The FDA is not required to follow the advice of its panels, though it usually does.
Selzentry is part of a recently developed class of treatments that block HIV from entering white blood cells through a pathway present in some patients. While more than 1 million people in the U.S. are HIV positive, only a subset of that group respond to Pfizer's pill. The drug works by blocking the so-called CCR5 receptor.
HIV attacks the body's immune system, eventually causing AIDS.
Pfizer said the meeting "marks an important step in expanding available treatment options for patients with HIV infection."
Selzentry had sales of $46 million last year, according to Pfizer.