By Saumya Joseph

(Reuters) – The U.S. Food and Drug Administration said on Tuesday it had approved Amgen Inc’s osteoporosis treatment for postmenopausal women who are at high risk of fracture.

Postmenopausal osteoporosis is a chronic condition resulting from progressive bone loss beginning around menopause.

The monthly injection, Evenity, developed jointly with Belgium-based UCB SA, helps reduce the risk of fracture by increasing bone mass and mildly inhibiting the break down of bone minerals.

Evenity comes with a boxed warning, the FDA’s strictest warning, flagging increased risk of heart attack, stroke and cardiovascular-related death.

The approval is expected to augment sales at Amgen, which faces competition from cheaper rivals for two of its biggest selling products – the white blood cell booster Neulasta and rheumatoid arthritis drug Enbrel.

However, William Blair analyst Matt Phipps expects the initial demand to be slow due to the cardiovascular risks, and expects peak sales of $500 million.

“It’s important to carefully select patients for this therapy, which includes avoiding use in patients who have had a heart attack or stroke within the previous year,” Hylton Joffe, a director at FDA’s Center for Drug Evaluation and Research, said.

Amgen said the drug would be launched next week and it will unveil the price of the drug as well.

The decision comes months after an FDA panel overwhelmingly voted for the drug’s approval.

Osteoporosis, most common in women who have reached menopause age, affects an estimated 8 million American women.

The market for such treatment is currently dominated by bone strengthening agents known as antiresorptive therapies, including Merck & Co’s Fosamax, which block the normal process of break down of bone minerals. But they take years to get a substantial benefit.

Evenity, which belongs to a new class of drugs known as sclerostin inhibitors, is administered with two 105 mg injections every month for a year, followed by chronic therapy with an antiresorptive drug.

(Reporting by Manas Mishra and Saumya Sibi Joseph in Bengaluru; Editing by Shounak Dasgupta and James Emmanuel)