Amgen won an earlier-than-expected FDA approval for denosumab, its treatment for postmenopausal women with osteoporosis at high risk for bone fractures, just days after European regulators approved the drug. Sales of the injectable medicine, to be marketed as Prolia, could generate as much as $942 million in 2011, according to consensus analyst estimates from Bloomberg. Sources polled by EvaluatePharma predicted sales of $5.32 billion by 2016.

“Due to its prevalence, osteoporosis is a serious concern to public health,” says Julie Beitz, director of the FDA’s Office of Drug Evaluation III.

Osteoporosis, a disease in which the bones become weak and are more likely to break, is a major public health threat for an estimated 44 million Americans, or 55 percent of the people 50 years of age and older, according to the National Osteoporosis Foundation.

“For the many osteoporosis patients who are at high risk for fracture, Prolia’s approval marks the first new class of medicine introduced in nearly a decade,” says Felicia Cosman, the foundation's clinical director.

“It will be a welcome new option,” she says.

One out of every two women over age 50 will break a bone in their lifetime due to osteoporosis, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

Amgen's hopes for Prolia go beyond the indication approved this month. It is still pursuing approvals for treating cancer-related bone damage, prevention of bone metastases in breast and prostate cancer and bone loss induced by hormone ablation cancer therapies. The company is running late stage trials for all those indications, but the FDA requested more data before agreeing to consider approving the drug for those uses.

Prolia will cost $1,650 per year for its two-injection course, according to Amgen, making its price competitive with other branded osteoporosis therapies the company says and it will be commercially available in the U.S. almost immediately.