The pharmacokinetics and pharmacodynamics of glipizide were evaluated in 20 patients with non-insulin-dependent diabetes mellitus (NIDDM). The group consisted of 12 obese subjects (seven women, five men; mean +/- SD age, 53.5 +/- 8.5 years; total body weight (TBW), 95.5 +/- 17.2 kg; percentage > IBW (ideal body weight), 57.8 +/- 31.7%); and eight nonobese subjects (two women, six men; age, 57.8 +/- 11.7 years; TBW, 80.8 +/- 9.9 kg; percentage > IBW, 15.6 +/- 10.3%). After a 2-week antidiabetic drug-free period, patients were started on glipizide therapy for 12 weeks. Glipizide dosages were titrated to achieve specified therapeutic goals or a maximum daily dose of 40 mg. Glipizide pharmacokinetics were assessed by serum concentrations obtained during a 24-h pharmacokinetic evaluation performed after the first 5-mg dose (SD) and after 12 weeks of chronic therapy (CD). Glipizide pharmacodynamics were evaluated with serum glucose, insulin, and C-peptide responses to Sustacal tolerance test done at baseline, after SD, and after CD. No statistically significant differences in the SD pharmacokinetic parameters (Tmax = 3.1 +/- 1.2 vs. 2.8 +/- 1.6 h; Cmax = 332.5 +/- 92.5 vs. 420.8 +/- 142 g/L; area under the curve extrapolated to infinity (AUCI) = 2,598.3 +/- 1,148 vs. 3,138.9 +/- 1,847 g/h/L; oral clearance/bioavailability (CL/F), 2.3 +/- 1.0 vs. 2.0 +/- 1.0 L/h; volume of distribution/bioavailability (V/F), 19.5 +/- 4.4 vs. 17.2 +/- 4.3 L; t1/2 = 5.0 +/- 2.3 vs. 5.2 +/- 2.0 h) were observed between the obese and nonobese groups, respectively. The pharmacokinetic parameters assessed under CD conditions were also closely matched in the two groups. No differences in glucose responses to Sustacal challenge at baseline, SD, and CD (AUC0-->4.glucose:baseline, 52.3 +/- 18.0 vs. 44.9 +/- 9.8; SD, 50.4 +/- 20.9 vs. 36.1 +/- 11.0; CD, 37.8 +/- 10.7 vs. 36.6 +/- 8.5 mM/h) were noted between the obese and nonobese groups, respectively. However, glucose concentrations increased more and decreased to a smaller extent after SD in the obese as compared to nonobese subjects. Mean fasting serum insulin and C-peptide concentrations were not statistically different between the two groups. However, obese subjects exhibited higher fasting insulin (114.0 +/- 69 vs. 68.8 +/- 52 pM) at week 12 evaluation and C-peptide concentrations (0.83 +/- 0.2 vs. 0.63 +/- 0.2 nM) after SD as compared to the nonobese group. A smaller percentage increase in C peptide in response to Sustacal challenge was observed in the obese compared to the nonobese subjects (baseline, 60 +/- 25 vs. 117 +/- 117; SD, 119 +/- 39 vs. 193 +/- 149; and CD, 97 +/- 56 vs. 163 +/- 67%). In summary, the influence of obesity on glipizide pharmacokinetics appeared to be of little clinical significance. The observed differences in pharmacodynamics require further evaluation.