Bioavailability of metformin in tablet form using a new high pressure liquid chromatography assay method

Twenty-four young healthy volunteers received a single dose of metformin 500 mg (Glucophage, Nordic Laboratories, Canada) in tablet form. Plasma concentrations were determined by HPLC in samples collected prior to and 0.33, 0.66, 1, 1.33, 1.66, 2, 2.5, 3, 4, 5, 6, 7, 8, 10, 12, 15, 18, 24, and 30 h after dosing. Mean (+/- SD) Cmax was 682.1 (160.6) ng ml-1 at a mean (+/- SD) tmax of 2.4 (0.93) h. Overall elimination was monoexponential with a mean (+/- SD) half-life of 3.16 (0.47) h. We conclude that metformin is rapidly absorbed from this formulation and is also rapidly eliminated. Extrapolation to steady state predicts that equilibrium will be reached within 24 h.