Amylin Pharmaceuticals and Alkermes' Bydureon, or exenatide, has been approved by the FDA as a once-weekly treatment for type 2 diabetes. The glucagonlike peptide-1 receptor agonist costs about $4,200 a year. Amylin is conducting an FDA-requested trial to determine whether Bydureon heightens the risk of heart attacks, thyroid cancer, and pancreatitis.