and Eli Lilly stumbled Monday after regulators warned of two deaths possibly related to the companies' Byetta diabetes drug.
Shares of Amylin fell 16%, to $28.86, while its partner Eli Lilly were off by 1.7%, at $47.94.
More than 80% of Amylin's first-half revenue in 2008 came from sales of Byetta.
The FDA said Monday that Byetta could be linked to six cases of severe pancreatitis, all of which required hospitalization. Two of the patients have died.
Regulators said there are no signs that would distinguish these types of severe pancreatitis (necrotizing or acute hemorrhagic) from less severe forms of pancreatitis.
The FDA said its working with Eli Lilly and Amylin to add stronger more prominent warnings in the product label around the risk of these severe forms of pancreatitis.