Rapid determination of metformin in human plasma by liquid chromatography−tandem mass spectrometry method

A rapid, sensitive and specific liquid chromatography−tandem mass spectrometry method is described for quantitation of metformin in human plasma. After a simple, one-step protein precipitation using acetonitrile, metformin and the internal standard diphenhydramine were chromatographed on a C8 column and detected by tandem mass spectrometry. An atmospheric pressure chemical ionization interface was chosen to reduce ion suppression from sample matrix components and provide high sensitivity. The method has a chromatographic total run time of 3.4 min and was linear within the range 2–2000 ng/ml. Intra- and inter-day precision, expressed as the relative standard deviation (R.S.D.), ranged from 4.4 to 5.7% and from 1.3 to 2.8%, respectively. Assay accuracy was less than 1% in terms of %RE (relative error). The assay was used to evaluate the pharmacokinetics of metformin after an oral administration of multicomponent formulation containing 500 mg metformin and 2.5 mg glyburide to 20 healthy volunteers.