Lasofoxifene (Oporia) is a product of a joint development programme between Pfizer and Ligand Pharmaceuticals, which is a selective estrogen receptor modulator (SERM) under development for the prevention and treatment of osteoporosis and for the treatment of vaginal atrophy. Osteoporosis affects nearly 8 million American women. An additional 22 million women are likely to have low bone mass, placing them at increased risk of osteoporosis. In the US osteoporosis is responsible for more than 1.5 million fractures every year. On the other hand, vaginal dryness becomes more and more common throughout the menopausal transition. SERMs offer benefits beyond just the bone effects provided by other treatment options such as bisphosphonates.

Lasofoxifene is currently under development and is not yet available on the market. Alternative uses for this drug have not been defined, and scientific research and studies are currently still in process.

Clinical Studies

Preclinical studies show Lasofoxifene binds to oestrogen receptors with an affinity comparable to that of 17beta-estradiol and, in bone, duplicates many of the effects obtained following administration of oestrogen. These properties suggest usefulness in osteoporosis and this is indeed confirmed in phase II trials. Compared with raloxifene, the current leading SERM, lasofoxifene appeared more effective in improving spinal bone density in post-menopausal women. Long-term phase II data show that the improvements in bone density are sustained after 2 years of dosing. Compared with raloxifene, long-term administration of Lasofoxifene significantly improved bone parameters, such as bone resorption and lumbar-spine bone mineral density. Reductions in LDL-C were also more distinct in the Lasofoxifene treatment arm compared with raloxifene.

Some 10,500 women have been enrolled in clinical trials in which the effect of Lasofoxifene on bone loss prevention and fractures is being assessed.