The US Food and Drug Administration yesterday approved Amgen’s bone-strengthening drug denosumab for use in postmenopausal women with osteoporosis. The medicine is expected to have sales totaling close to $1 billion next year, according to Bloomberg.

The announcement comes less than a week after the drug, to be marketed under the brand name Prolia, was given the nod by European regulators. Prolia remains under review in Switzerland, Australia and Canada.

Amgen’s drug is the first and only approved therapy that specifically targets the nuclear factor-κB ligand (RANKL), an essential regulator of the cells that break down bone. Prolia’s assent was based on a study of more than 7,800 women with osteoporosis. Compared to placebo, the medicine — administered as a 60mg injection every six months — reduced vertebral, hip and non-vertebral fractures by 20% to 68%.

But Prolia may have a hard time competing with Merck’s Fosamax, one of the best-selling brand-name drugs in the world. Even though Prolia somewhat outperformed Fosamax in head-to-head trials for some bone traits, price could be a factor. Once-a-week, orally-delivered Fosamax is now generic and costs as little as $400 per year; Prolia, in contrast, is expected to cost more than four times as much.

To learn more about another potential osteoporosis therapy in the pipeline, watch this video covering a paper published earlier this year in this journal.

Image: Nature Medicine 15, 144-145 (2009).