title: 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.
  
  
  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 m(2) body surface.
  
  
  RESULTS
  Patients with eGFR >60, 30-60, and <30 ml/min/1.73 m(2) had median trough metformin concentrations of 4.5 micromol/l (range 0.1-20.7, n = 107), 7.71 micromol/l (0.12-15.15, n = 21), and 8.88 micromol/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 micromol/l. Metformin measurement is less suitable for dose titration.
authors.affiliation: Department of Endocrinology, University Hospital MAS, Malmö, Sweden. anders.frid@skane.se
authors.forename: Anders
authors.initials: A
authors.lastname: Frid
authors.forename: Gunnar N
authors.initials: GN
authors.lastname: Sterner
authors.forename: Magnus
authors.initials: M
authors.lastname: Löndahl
authors.forename: Clara
authors.initials: C
authors.lastname: Wiklander
authors.forename: Anne
authors.initials: A
authors.lastname: Cato
authors.forename: Ellen
authors.initials: E
authors.lastname: Vinge
authors.forename: Anders
authors.initials: A
authors.lastname: Andersson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001681:Biological Assay / Q000379:methods*; D002851:Chromatography, High Pressure Liquid; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000188:drug therapy*; D005260:Female; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000097:blood / Q000494:pharmacology / Q000627:therapeutic use; D007677:Kidney Function Tests; D008297:Male; D013058:Mass Spectrometry; D008687:Metformin / Q000097:blood* / Q000494:pharmacology / Q000627:therapeutic use; D008875:Middle Aged
chemical_list: D007004:Hypoglycemic Agents; D008687:Metformin