Novel Assay of Metformin Levels in Patients With Type 2 Diabetes and Varying Levels of Renal Function

To study trough levels of metformin in serum and its intra-individual variation in patients using a newly developed assay. Trough serum levels of metformin were measured once using liquid chromatography-tandem mass spectrometry (LCMSMS) in 137 type 2 diabetic patients with varying renal function (99 men) and followed repeatedly during 2 months in 20 patients (16 men) with estimated glomerular filtration rate (eGFR) 60, 30-60, and 20 µmol/l. Metformin measurement is less suitable for dose titration.