Pfizer Inc. (PFE) plans to explore the sale or licensing of osteoporosis drug Fablyn, which has been approved for sale in Europe but held up by regulators in the U.S., possibly due to safety concerns.

The New York-based drug giant disclosed its plan to pursue strategic options for Fablyn in regulatory filings Thursday and in May, but the plans haven't been widely publicized. Wall Street expectations for the drug's financial performance were already low because of Pfizer's past difficulties in getting the drug approved.

The European Commission approved Fablyn earlier this year for the treatment of osteoporosis in post-menopausal women at increased risk of fracture.

But in January, the U.S. Food and Drug Administration issued a so-called "complete response" letter to Pfizer's application to market Fablyn in the U.S., requesting additional information before it could make a final decision.

The FDA delay followed a September 2008 recommendation by an FDA advisory committee that the drug had benefits for certain post-menopausal women, though it should be restricted to those at high risk of fracture or those who fail other treatments. FDA staff had raised concerns that Fablyn puts patients at higher risk of death than a fake drug, but outside advisers said there weren't enough definitive data on that issue.

After the FDA's letter in January, and "following a strategic review, we decided to explore strategic options for Fablyn, including out-licensing or sale," Pfizer said in its regulatory filing.

Pfizer representatives weren't immediately available Friday to elaborate.

Pfizer executives signaled earlier this year the company was seeking to license out dozens of its experimental drugs because they were in disease areas that are no longer top Pfizer priorities.

In addition, Pfizer is in the process of acquiring Wyeth (WYE), which has developed a similar osteoporosis drug, bazedoxifene, that received European regulatory approval in April. The drug is being marketed as Conbriza in Europe. Wyeth also is pursuing U.S. regulatory approval for the drug under the brand Viviant.

Pfizer had been seeking FDA approval of Fablyn for years. In 2005 and 2006, the FDA rejected Pfizer's applications to market the drug for the prevention of post-menopausal osteoporosis and for treatment of vaginal atrophy.

Both Pfizer and Wyeth co-developed their respective osteoporosis drugs under collaborations with Ligand Pharmaceuticals Inc. (LGND).

Ligand representatives couldn't immediately be reached.

Pfizer shares rose 30 cents to $16.09; Wyeth was 42 cents higher at $47.13; and Ligand shares were up 9 cents at $2.95.

-Peter Loftus; Dow Jones Newswires; 215-656-8289; peter.loftus@dowjones.com

(Thomas Gryta and Jared Favole contributed to this article.)