COMPARISON OF PHARMACOKINETICS AND PHARMACODYNAMICS OF SHORT-TERM AND LONG-TERM GLYBURIDE THERAPY IN NIDDM

OBJECTIVE - To examine the pharmacokinetics and pharmacodynamics of glyburide after single- and multiple-dose administration in patients with type II diabetes. RESEARCH DESIGN AND METHODS - Twenty patients with type II diabetes between 40 and 70 years of age participated in the study. A 24-h pharmacokinetic evaluation including a 4-h Sustacal tolerance test was conducted before instituting glyburide therapy (baseline), after the first 2.5-mg test dose of glyburide and at weeks 6 and 12 of chronic glyburide therapy. Glyburide doses were titrated with a target goal of achieving a fasting plasma glucose of less than or equal to 7.8 mmol/l or to reach maximum daily doses of 20 mg. RESULTS - A significant prolongation in the elimination half-life (t(1/2): week 0, 4.0 +/- 1.9 h; week 6, 13.7 +/- 10.5 h; and week 12, 12.1 +/- 8.2 h) and an increased volume of distribution of glyburide was observed during chronic dosing. These results strongly suggest possible drug accumulation. No differences in pharmacokinetic parameters were noted between evaluations at week 6 or week 12. Changes in pharmacodynamic response of glucose, insulin, and C-peptide to chronic glyburide therapy were observed. Glyburide therapy significantly reduced plasma glucose levels at weeks 6 and 12 (percent changes in AUCO(0-->4.glucose) from baseline: week 0, -3 +/- 11%; week 6, -29 +/- 13%; and week 12, -26 +/- 19%). Pancreatic insulin secretion was acutely enhanced and maintained during long-term therapy. Responsiveness to therapy as assessed by the ratio of AUC(0-->4.glucose):AUC(0-->4.C-peptide) was significantly improved at all weeks compared with baseline. No pharmacodynamic response differences were observed between the week 6 and the week 12 evaluations. CONCLUSIONS - This study demonstrates that significant differences in glyburide pharmacokinetics and pharmacodynamics exist between single-dose and steady-state conditions. These differences support the need for careful dosage titration of glyburide to achieve a desired therapeutic response in patients with type II diabetes.