Comparative Efficacy and Potency of Long-Term Therapy with Glipizide or Glyburide in Patients with Type 2 Diabetes Mellitus

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Long-term studies on the comparative efficacy and relative potency of glipizide and glyburide are sparse and controversial. In a randomized prospective trial, we compared the effectiveness and relative potency of glipizide and glyburide over a 15-month period in 18 patients with type 2 diabetes mellitus (DM2) (9 on glyburide and 9 on glipizide) who were unresponsive to diet therapy. Glycemic control was assessed using 4 methods: 1) quarterly fasting plasma glucose (FPG), and 2-hour postprandial plasma glucose after a standard breakfast; 2) insulin and glucose response to Sustacal (test meal) challenge every 3 to 6 months; 3) quarterly hemoglobin A1c; and 4) intravenous glucose tolerance testing every 6 months to measure first and second phase insulin secretion. Patient characteristics were similar in each treatment group. Similar doses of glipizide (11 mg/day) or glyburide (10 mg/day) resulted in comparable reduction of FPG and hemoglobin A1c and increase in first phase insulin response to intravenous glucose tolerance testing. There was greater reduction in FPG and 2-hour postprandial plasma glucose with glipizide than with glyburide in 6 months. Contrary to the Physicians' Desk Reference, but consistent with another short-term study, our long-term study demonstrated that glipizide and glyburide are equipotent at similar doses in controlling hyperglycemia in DM2. Glipizide and glyburide are effective in controlling hyperglycemia with similar doses in DM2. Glipizide exhibits greater reduction in FPG and 2PPG at 6 months. Additional studies are needed to validate equipotency of these drugs.