The US Food and Drug Administration (FDA) has issued a second approvable letter to Wyeth Pharmaceuticals, demanding the company to answer several remaining questions regarding its experimental osteoporosis drug bazedoxifene.

Bazedoxifene is a selective oestrogen receptor modulator, for the prevention of postmenopausal osteoporosis.

In its letter, the FDA identified several remaining questions regarding issues that had been previously identified during the review process and that were not fully resolved by the company's complete response to the first approvable letter. The FDA has requested further analyses and discussion concerning the incidence of stroke and venous thrombotic events. The Agency also identified certain issues concerning data collection and reporting and requested additional source documents.

The FDA stated that the Wyeth Asian studies that were submitted on November 9 and December 14, 2007, were not reviewed for this action. Wyeth believes the data from these nearly 1,000 women provide additional support for a favourable benefit to risk ratio for bazedoxifene in the prevention of postmenopausal osteoporosis.

The Agency did not request the initiation of any new studies and has suggested an end-of-review conference between Wyeth and the FDA to address the remaining issues.

"We look forward to working with the FDA to resolve these issues. Wyeth is dedicated to identifying therapies for the millions of postmenopausal women who are at risk for increased bone loss," said Gary L. Stiles, M.D., executive vice president, chief medical officer, Wyeth Pharmaceuticals.

The company received the first approvable letter on April 23, 2007, and submitted data requested in June 2007. In July 2007, Wyeth submitted a separate New Drug Application to the FDA for bazedoxifene for the treatment of postmenopausal osteoporosis, which was accepted for filing in September 2007, with an action date in May 2008.

Osteoporosis is a disease characterised by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased risk of fractures. Up to 20 per cent of a woman's expected lifetime bone loss can occur in the years immediately following menopause. The prevention of postmenopausal osteoporosis could lead to significant improvement in the overall health for millions of women worldwide as well as reduce costs associated with the treatment of postmenopausal osteoporosis-related fractures.

Wyeth Pharmaceuticals, a division of Wyeth, has leading products in the areas of women's health care, infectious disease, gastrointestinal health, central nervous system, inflammation, transplantation, haemophilia, oncology, vaccines and nutritional products.