Purpose: To study the efficacy and safety of various dosages of metformin as compared with placebo in patients with type II diabetes mellitus.
Patients and methods: A 14-week, multicenter, double-blind, dose-response study was conducted. After a 3-week, single-blind, placebo-controlled washout, 451 patients with fasting plasma glucose levels of at least 180 mg/dL were randomized to receive an 11-week course of placebo or metformin given at 500, 1000, 1500, 2000, or 2500 mg daily.
Results: Metformin improved glucose variables as compared with placebo. The adjusted mean changes in fasting plasma glucose from baseline associated with each metformin group at week 7, 11, or at endpoint exceeded those associated with placebo by 19 to 84 mg/dL at dosages of 500 to 2000 mg daily, respectively. The corresponding between-group differences in glycated hemoglobin (HbA1c) ranged from 0.6% to 2.0% at dosages of 500 to 2000 mg daily, respectively. All between-group differences were significant (P < 0.05) for both fasting plasma glucose and HbA1c at week 7, week 11, and endpoint, except for the difference between placebo and metformin 500 mg in fasting plasma glucose at endpoint (P = 0.054). Treatment-related adverse events occurred in 15% of patients in the placebo group and in 28% in the metformin group (P = 0.02); these were primarily manifested as digestive disturbances, such as diarrhea.
Conclusions: Metformin lowered fasting plasma glucose and HbA1c generally in a dose-related manner. Benefits were observed with as little as 500 mg of metformin; maximal benefits were observed at the upper limits of the recommended daily dosage. All dosages were well tolerated. Metformin appears to be a useful therapeutic option for physicians who wish to titrate drug therapy to achieve target glucose concentrations.