Glipizide versus tolbutamide, an open trial. Effects on insulin secretory patterns and glucose concentrations.

An open parallel trial with glipizide or tolbutamide was carried out in a cohort of 29 comparable maturity-onset diabetic patients. Eighteen of these individuals were studied in detail. During six months of active drug therapy the mean decrease in fasting serum glucose levels on glipizide was 25 +/- 2% versus 17 +/- 2% on tolbutamide (p less than 0.025). Decreases in post prandial glucose levels were 12.2 and 10.4%. Glucose disappearance rates (Kg) during the sixth month of treatment with both drugs increased significantly: on glipizide from 0.47 +/- 0.04%/min to 0.85 +/- 0.08%/min(p less than 0.005), and on tolbutamide from 0.47 +/- 0.08%/min to 0.70 +/- 0.11%/min (p less than 0.01). Early and late insulin release (summed increases over basal for 2--10 min and 10--60 min) during intravenous glucose tolerance testing increased during glipizide, but not during tolbutamide therapy. Post prandial insulin increments over basal during an oral glucose tolerance test also increased during glipizide, but not tolbutamide therapy. Both drugs were comparable with regard to efficacy and safety; however, only glipizide had chronic effects upon insulin secretion.