Comparative Efficacy of a Once-Daily Controlled-Release Formulation of Glipizide and Immediate-Release Glipizide in Patients With NIDDM

OBJECTIVE: To compare the efficacy and safety of controlled-release glipizide (glipizide-GITS [gastrointestinal therapeutic system]) and immediate-release glipizide in patients with non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS: In a multicenter, open-label, randomized, two-way crossover study, 132 patients with NIDDM received daily doses of 5, 20, or 40 mg of either glipizide-GITS or immediate-release glipizide for 8 weeks followed by 8 weeks of the alternate formulation. Plasma glucose, serum insulin, C-peptide, and plasma glipizide levels were measured at fasting and post-Sustacal challenge at the end of 1 and 8 weeks of each treatment phase. HbA1c was measured at the end of weeks 7 and 8 of each treatment phase. RESULTS: Both formulations of glipizide yielded similar mean HbA1c values. However, mean fasting plasma glucose (FPG) levels were significantly lower with glipizide-GITS treatment than with immediate-release glipizide at the end of week 1 (11.0 vs. 11.6 mmol/l; P < 0.01) and at the end of the 8-week treatment phase (10.9 vs. 11.7 mmol/l; P < 0.001). Fasting insulin and C-peptide levels were lower after 5 mg glipizide-GITS vs. immediate-release glipizide. Glucose responses to Sustacal were similar after both formulations of glipizide; however, serum insulin (P < 0.01) and C-peptide responses (P < 0.05) were lower with glipizide-GITS than with immediate-release glipizide treatment at the end of the 8-week treatment phase. Mean plasma glipizide concentrations were stable by the end of week 1, and the concentrations increased proportionately with dose. Once-daily Glipizide-GITS provided effective mean glipizide concentrations (> 50 ng/ml) 24 h after dosing, even at the lowest (5 mg) dose level. Both formulations were well tolerated. CONCLUSIONS: Glipizide-GITS was significantly more effective than immediate-release glipizide in reducing FPG levels. Both formulations reduced postprandial plasma glucose levels equally; however, glipizide-GITS exerted its control in the presence of lower plasma glipizide concentrations in addition to significantly lower insulin and C-peptide levels. This suggests that glipizide-GITS improves insulin sensitivity.