Pfizer has received a somewhat unexpected boost with the news that an advisory panel in the USA has given its backing to the firm’s osteoporosis drug Fablyn, which has been rejected twice in the past.

The Advisory Committee for Reproductive Health Drugs at the US Food and Drug Administration have voted 9-3 that the benefits of once-daily Fablyn (lasofoxifene), a selective estrogen receptor modulator, outweigh the risks. One panellist abstained.

The thumbs-up from the panellists is a bit of a surprise given that it follows briefing documents posted ahead of the meeting by FDA staffers who noted that patients who took the lowest dose of the drug (0.25mg), which is developed using technology from Ligand Pharmaceuticals, had a higher incidence of blood clots and deaths compared with the group on placebo. However the staffers also noted that patients taking Fablyn 0.5mg were at a lower risk, ie 41% less likely, of developing spine fractures compared to placebo.

A majority of panel members said they were unable to tell if the rise in deaths was due to patients taking the low dose of the drug. Pfizer had said that the increased number of deaths "appears to be due to an unusually low mortality rate for the placebo group”.

Scott Monroe, director of the FDA's Division of Reproductive and Urologic Products, said that thje vote should not be seen as a ”clear-cut endorsement'' for Fablyn but Pfizer is understandably pleased. The New York-based behemoth said the data demonstrates that lasofoxifene “offers unique benefits for the treatment of osteoporosis in women at increased risk of fractures,'' noting that “we will continue to work with FDA on any outstanding questions''.

The path towards possible approval for Fablyn has been less than smooth. In 2005, the FDA rejected an application for the drug - then called Oporia - for prevention of osteoporosis and in 2006 turned down a second indication of vaginal atrophy. Both of those not approvable letters were due due to concerns about an increased risk of endometrial cancer, but Pfizer resubmitted the drug with new data after completing a five-year study involving more than 9,000 women

The FDA usually follows the recommendations of its panellists but analysts are not sure the agency will this time. Catherine Arnold at Credit Suisse issued a note saying that “given the amount of discussion at today’s meeting on the benefit-to-risk ratio for Fablyn, we are not convinced that the FDA will definitely approve the drug”. If approved, however, analysts are saying the treatment could become a blockbuster.