tokens: Metformin plasma concentrations remained unchanged except for patients transferred from 1 . 5 to 2 . 0 g daily to 850 mg twice daily ; in these patients plasma concentrations increased from 1 . 83 + / - 0 . 87 to 2 . 50 + / - 0 . 89 micrograms / l ( p less than 0 . 01 ) .