Establishment of a Database of Metformin Plasma Concentrations and Erythrocyte Levels in Normal and Emergency Situations

Background and Objectives: Knowledge of blood metformin concentrations may be crucial for adapting the dose to the patient's kidney function and investigating a putative link between this drug and lactic acidosis. We therefore established the first database of blood metformin concentrations. Methods: In order to provide cross-sectional data from clinical practice in a university medical centre, the authors retrospectively reviewed all available metformin plasma concentrations and erythrocyte level results (all of which were measured using the same assay technique). The assays had been requested for either dose adjustment in relation to the patient's renal status or screening for potential metformin accumulation, metformin overdose or lactic acidosis. Results: A total of 798 metformin assays were performed in 467 patients. The mean +/- SD (range) plasma concentrations and erythrocyte levels were 2.7 +/- 7.3 (0-113) mg/L and 2.0 +/- 4.4 (0-61) mg/L, respectively (published therapeutic values: 0.5 +/- 0.4 mg/L and 0.8 +/- 0.4 mg/L, respectively). Four plasma concentration categories were defined on a pragmatic basis: undetectable (9.7%), therapeutic range (40.6%), slight-to-moderate elevation (42.6%) and marked elevation (7.1%). Conclusion: Greater knowledge of blood metformin concentrations is required to adjust treatment and avoid wrongly incriminating the drug in lactic acidosis. Establishment of the first database of blood metformin concentrations may help physicians to better evaluate metformin use and dosage levels (particularly in elderly patients and those with poor kidney function), determine the presence and intensity of metformin accumulation and, ultimately, establish the prognosis of the latter condition.