Sulfonylurea: A class of oral hypoglycemic agents (medications that lower the level of blood glucose) taken by people with type 2 diabetes. The sulfonylureas increase the secretion of insulin by the pancreas. There are two generations of sulfonylureas. The main difference between the first- and second-generation sulfonylureas is in the way they are 'eliminated from the body. As a consequence, second-generation sulfonylureas are usually taken less 'frequently each day than first-generation sulfonylureas and generally are preferred when there is poor function of the kidneys. Examples of first-'generation sulfonylureas are chlorpropamide (Diabinese) and tolbutamide (Orinase). The second-generation sulfonylureas include glipizide (Glucotrol and Glucotrol XL), glyburide (Diabeta, Micronase, and Glynase PresTab), and glimepiride (Amaryl). These drugs are effective in rapidly 'lowering blood sugar but run the risk of causing hypoglycemia.