Repaglinide (Meglitinide / Nonsulfonylurea Secretagogue)

• Repaglinide binds to the sulfonylurea receptor (SUR1) subunit of the K_ATP channel on pancreatic β cells. It shares two of its three molecular binding sites with sulfonylureas but also has one unique binding site, giving it a distinct pharmacologic profile (Goodman & Gilman's, p. 1054-1057; Katzung's, p. 1185).
• Binding closes the K_ATP channel, which reduces K+ efflux and depolarizes the β-cell membrane.
• Depolarization opens voltage-gated Ca2+ channels, Ca2+ influx triggers exocytosis of insulin-containing granules, so insulin secretion increases - the same downstream pathway as sulfonylureas, but through a chemically distinct binding site.
• Key functional difference from sulfonylureas: rapid onset (peak effect within about 1 hour) and short duration of action (2-6 hours), making it a "postprandial glucose regulator." It is taken just before each meal to blunt the post-meal glucose excursion rather than providing sustained basal secretagogue activity (Lippincott Illustrated Reviews Pharmacology, p. 814-815; Katzung's, p. 1185).
• Metabolized by CYP2C8/CYP3A4 in the liver to inactive metabolites, excreted mainly in feces - useful in renal impairment. Gemfibrozil markedly increases repaglinide levels (contraindicated combination); it should not be combined with sulfonylureas because of overlapping mechanism and additive hypoglycemia risk.

Voglibose (Alpha-Glucosidase Inhibitor)

• Voglibose, like acarbose and miglitol, competitively and reversibly inhibits intestinal α-glucosidases (glucoamylase, sucrase, maltase, isomaltase) located on the brush border of enterocytes in the upper small intestine (Goodman & Gilman's, p. 1058-1059; Katzung's, p. 1186).
• Normally these enzymes break down dietary starches and disaccharides into absorbable monosaccharides. By inhibiting them, voglibose delays and reduces the breakdown and absorption of complex carbohydrates.
• Carbohydrate digestion is pushed distally along the small intestine, flattening and delaying the postprandial glucose rise rather than blocking glucose absorption altogether.
• It also increases release of GLP-1, which may contribute modestly to its glucose-lowering effect.
• It does not stimulate insulin release and carries essentially no risk of hypoglycemia when used alone. Because undigested carbohydrate reaches the colon and is fermented by bacteria, the main adverse effects are flatulence, bloating, and diarrhea.
• Voglibose is not marketed in the US but is used in Japan, Korea, and India; acarbose and miglitol are the analogous agents available in the US.

Key contrast