NEW YORK, New York—Pfizer's experimental osteoporosis drug Fablyn (lasofoxifene) has so far failed to win US Food and Drug Association (FDA) approval.

Although an FDA advisory panel concluded Sept. 8 that the drug's benefits outweigh its risks, an FDA staff review raised troubling questions about stroke, cancer, blood clots, and gynecological problems in women treated with the drug.

The company said in a statement that it “will work with the FDA to determine the appropriate next steps regarding the application.”

Fablyn would be an important new product for Pfizer, since Lipitor, a $12.7 billion/year drug, goes off patent in 2011. Analysts had expected Fablyn to have $500 million in annual sales.

The drug was tested in 8,500 women and cut the rate of new fractures nearly in half, but the FDA staff review concluded that a low dose of Fablyn was linked to more deaths from cancer and stroke. Pfizer disputed the causal relationship, pointing to an unusually low mortality rate in the control group. The company was seeking approval to sell a higher, 0.5-milligram dose, which was not associated with increased mortality.

Meanwhile, the European Medicines Agency's Committee for Medicinal Products for Human Use (CHMP) issued a positive opinion on December 18, 2008, recommending marketing authorization for lasofoxifene.

Lasofoxifene is a selective estrogen receptor modulator, or SERM, in the same chemical class as raloxifene.