U.S. seeks more warnings for Amylin diabetes drug

"We do remain very confident in the development program of our once-weekly" formulation of Byetta, she told Reuters.

No pancreatitis cases have been seen in Byetta LAR trials so far, she said.

The shares of Alkermes Inc, maker of technology used to develop the new version, known as Byetta LAR, closed down 10 percent at $14.73 on Nasdaq.

Byetta, also know by its chemical name, exenatide, is taken with other diabetes medicines to help lower blood sugar levels by regulating insulin production. The first in a new class of drugs called incretin memetics, it posted $636 million in 2007 net product sales, according to Amylin.

Pancreatitis is an inflammation of the pancreas, which helps aid in digestion by releasing vital hormones. The condition usually subsides within a week, according to the National Institutes of Health.

But in some patients taking Byetta, the condition worsened.

"There are no signs or symptoms that distinguish acute hemorrhagic or necrotizing pancreatitis associated with Byetta from the less severe form of pancreatitis," the FDA said.

Doctors should discontinue use of the drug and monitor patients carefully, it added.

(Additional reporting by Ransdell Pierson in New York and Toni Clarke in Boston; Editing by Maureen Bavdek and Andre Grenon)