Sulfonylureas lower blood glucose in patients with NIDDM by directly stimulating the acute release of insulin from functioning beta cells of pancreatic islet tissue by an unknown process that involves a sulfonylurea receptor (receptor 1) on the beta cell. Sulfonylureas inhibit the ATP-potassium channels on the beta cell membrane and potassium efflux, which results in depolarization and calcium influx, calcium-calmodulin binding, kinase activation, and release of insulin-containing granules by exocytosis, an effect similar to that of glucose.
Tolbutamide, a first-generation sulfonylurea antidiabetic agent, is used with diet to lower blood glucose levels in patients with diabetes mellitus type II. Tolbutamide is twice as potent as the related second-generation agent glipizide. Tolbutamide lowers blood sugar by stimulating the pancreas to secrete insulin and helping the body use insulin efficiently. The pancreas must be able to produce insulin for this drug to work.
Metabolized in the liver principally via oxidation of the p-methyl group producing the carboxyl metabolite, 1-butyl-3-p-carboxyphenylsulfonylurea. May also be metabolized to hydroxytolbutamide. Tolbutamide does not undergo acetylation like antibacterial sulfonamides as it does not have a p-amino group.
Oral, mouse: LD50 = 2600 mg/kg