(Reuters) - An advisory panel to the U.S. Food and Drug Administration said on Wednesday that benefits of Amgen Inc’s osteoporosis treatment for postmenopausal women at high risk for fracture outweighed its risks and overwhelmingly voted for the drug’s approval.

FILE PHOTO: An Amgen sign is seen at the company's office in South San Francisco, California in this October 21, 2013 photo. REUTERS/Robert Galbraith/File Photo

The panel voted 16-1 in favor of the monthly injection developed jointly with Belgium-based UCB SA. The drug, Evenity, helps reduce the risk of fracture by increasing bone formation and inhibiting break down of bone minerals.

Three of the 19-member panel initially voted in favor of a different indication but one of them later said he meant to support the proposed use.

The panel, however, raised concerns of cardiovascular safety risks linked to the drug, which FDA staff reviewers on Monday had cited as the main reason for convening the panel meeting.

“I don’t think we’ve adequately characterized cardiovascular safety ... I don’t know the perfect solution but relying on observational data only post approval, I don’t think, will help us answer this reliably,” said panel member Pamela Shaw, who voted in favor of the drug’s approval.

“My vote is relying on a high-quality post-marketing study.”

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

An estimated 8 million American women live with the condition, which puts them at an increased risk of fractures, according to the National Osteoporosis Foundation.

Amgen had proposed approval with a boxed warning - the FDA’s harshest - highlighting the heart safety risks associated with Evenity.

“The efficacy of the drug was superb. If I had to bet, I’d bet that the cardiovascular issue would turn out to be spurious ... I hope (Amgen) will do a study that will get rid of the blackbox,” said Glenn Braunstein, another member who voted “yes”.

Jefferies analyst Michael Yee said a boxed warning would still represent an over $500 million revenue opportunity worldwide for Amgen.

Eli Lilly and Co’s osteoporosis drug Forteo brought in $1.75 billion sales in 2017 despite having a boxed warning.

Evenity, chemically known as romosozumab, belongs to a new class of drugs known as sclerostin inhibitors and is administered as an under-the-skin injection.

Amgen and UCB in 2017 received a complete response letter for the drug from the FDA, which requested data from an additional study to be included in their marketing application.

The FDA is not mandated to follow the recommendation of the panel, but generally does.