Novel assay of metformin levels in patients with type 2 diabetes and varying levels of renal function: Clinical recommendations

Abstract

OBJECTIVE- To study trough levels of metformin in serum and its intra-individual variation in patients using a newly developed assay. RESEARCH DESIGN AND METHODS- 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 ml/min/ 1.73 m2 body surface. RESULTS- Patients with eGFR >60, 30-60, and <30 ml/min/1.73 m2 had median trough metformin concentrations of 4.5 μmol/l (range 0.1-20.7, n = 107), 7.71 μmol/l (0.12-15.15, n = 21), and 8.88 μmol/l (5.99 -18.60, n = 9), respectively. The median intra-individual overall coefficient of variation was 29.4% (range 9.8 -74.2). CONCLUSIONS- Determination of serum metformin with the LCMSMS technique is useful in patients on metformin treatment. Few patients had values >20 μmol/l. Metformin measurement is less suitable for dose titration. © 2010 by the American Diabetes Association.