Sulfonylureas such as acetohexamide bind to an ATP-dependent K+ channel on the cell membrane of pancreatic beta cells. This inhibits a tonic, hyperpolarizing outflux of potassium, which causes the electric potential over the membrane to become more positive. This depolarization opens voltage-gated Ca2+ channels. The rise in intracellular calcium leads to increased fusion of insulin granulae with the cell membrane, and therefore increased secretion of (pro)insulin.
Acetohexamide is an intermediate-acting, first-generation oral sulfonylurea. It lowers blood sugar by stimulating the pancreatic beta cells to secrete insulin and by helping the body use insulin efficiently. The pancreas must produce insulin for this medication to work. Acetohexamide has one-third the potency of chlorpropamide, and twice the potency of tolbutamide; however, similar hypoglycemic efficacy occurs with equipotent dosage of sulfonylureas.
Extensively metabolized in the liver to the active metabolite hydroxyhexamide, which exhibits greater hypoglycemic potency than acetohexamide. Hydroxyhexamide is believed to be responsible for prolonged hypoglycemic effects.
Oral, rat LD50: 5 gm/kg; Oral, mouse LD50: >2500 mg/kg. Symptoms of an acetohexamide overdose include hunger, nausea, anxiety, cold sweats, weakness, drowsiness, unconsciousness, and coma.