Amylin shares fell more than 8 percent on Monday after data from an important diabetes meeting sparked concern about competition to the company's flagship Byetta medicine which Amylin sells with Eli Lilly .
Byetta has been the only drug on the market in the GLP-1 class of medicines that stimulate the release of insulin only when glucose levels become too high. They also lead to modest weight loss, which is seen as an advantage over other types of diabetes medicines, because obesity is a leading cause of the disease.
The drop continued a slide for Amylin, which fell more than 8 percent on Friday after Novo Nordisk released data showing its experimental drug liraglutide outperformed Byetta in a clinical trial.