Drug Groups

approved

Description

Glyburide is an oral antihyperglycemic agent used for the treatment of non-insulin-dependent diabetes mellitus (NIDDM). It belongs to the sulfonylurea class of insulin secretagogues, which act by stimulating β cells of the pancreas to release insulin. Sulfonylureas increase both basal insulin secretion and meal-stimulated insulin release. Medications in this class differ in their dose, rate of absorption, duration of action, route of elimination and binding site on their target pancreatic β cell receptor. Sulfonylureas also increase peripheral glucose utilization, decrease hepatic gluconeogenesis and may increase the number and sensitivity of insulin receptors. Sulfonylureas are associated with weight gain, though less so than insulin. Due to their mechanism of action, sulfonylureas may cause hypoglycemia and require consistent food intake to decrease this risk. The risk of hypoglycemia is increased in elderly, debilitated and malnourished individuals. Glyburide has been shown to decrease fasting plasma glucose, postprandial blood glucose and glycosolated hemoglobin (HbA1c) levels (reflective of the last 8-10 weeks of glucose control). Glyburide appears to be completely metabolized, likely in the liver. Although its metabolites exert a small hypoglycemic effect, their contribution to glyburide's hypoglycemic effect is thought to be clinically unimportant. Glyburide metabolites are excreted in urine and feces in approximately equal proportions. The half-life of glyburide appears to be unaffected in those with a creatinine clearance of greater than 29 ml/min/1.73m².

Indication

Indicated as an adjunct to diet to lower the blood glucose in patients with NIDDM whose hyperglycemia cannot be satisfactorily controlled by diet alone.

Pharmacology

Glyburide, a second-generation sulfonylurea antidiabetic agent, lowers blood glucose acutely by stimulating the release of insulin from the pancreas, an effect dependent upon functioning beta cells in the pancreatic islets. With chronic administration in Type II diabetic patients, the blood glucose lowering effect persists despite a gradual decline in the insulin secretory response to the drug. Extrapancreatic effects may be involved in the mechanism of action of oral sulfonyl-urea hypoglycemic drugs. The combination of glibenclamide and metformin may have a synergistic effect, since both agents act to improve glucose tolerance by different but complementary mechanisms. In addition to its blood glucose lowering actions, glyburide produces a mild diuresis by enhancement of renal free water clearance. Glyburide is twice as potent as the related second-generation agent glipizide.

Toxicity

Oral rat LD₅₀: > 20,000 mg/kg. Oral mouse LD₅₀: 3250 mg/kg.

Affected Organisms

Biotransformation

Primarily hepatic (mainly cytochrome P450 3A4). The major metabolite is the 4-trans-hydroxy derivative. A second metabolite, the 3-cis-hydroxy derivative, also occurs. These metabolites do not contribute clinically significant hypoglycemic action in humans as they are only weakly active; however, retention of 4-trans-hydroxyglyburide may prolong the hypoglycemic effect of the agent in those with severe renal impairment.

Absorption

Significant absorption within 1 hour and peak plasma levels are reached in 2 to 4 hours. Onset of action occurs within one hour.

Half Life

1.4-1.8 hours (unchanged drug only); 10 hours (metabolites included). Duration of effect is 12-24 hours.

Protein Binding

Unchanged drug is ~99% bound to serum proteins; 4-trans-hydroxyglyburide is greater than 97% bound to serum proteins. Protein binding is primarily nonionic making glyburide and is less likely to displace or be displaced by drugs that bind via an ionic mechanism.

Elimination

Glyburide is excreted as metabolites in the bile and urine, approximately 50% by each route.
This dual excretory pathway is qualitatively different from that of other sulfonylureas, which are excreted primarily in the urine.

Distribution

Steady state V_d=0.125 L/kg; V_d during elimination phase=0.155 L/kg.

Clearance

78 ml/hr/kg in healthy adults. Clearance may be substantially decreased in those with severe renal impairment.

References

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