Clinical question: Does metformin increase the risk of lactic acidosis in chronic kidney disease (CKD)?
Background: Metformin is first-line therapy for type 2 diabetes mellitus (DM) because of its low cost, safety, and potential cardiovascular benefit, but fear of lactic acidosis has limited its use in CKD. The risk of acidosis in CKD patients with varying levels of renal function has not been clearly defined.
Study design: Retrospective community-based cohort study.
Setting: Geisinger Health System in Pennsylvania.
Synopsis: A total of 75,413 patients were identified with diagnostic codes or medication prescriptions indicating DM. Forty-five percent of patients were taking metformin at enrollment, increasing by 18% over the 5.7 years of median follow-up. The primary outcome was inpatient acidosis, defined by an ICD-9-CM code capturing multiple forms of acidosis but excluding diabetic ketoacidosis.
When metformin users and nonusers were compared, risk of acidosis was similar for the entire cohort and for subgroups of patients with an estimated glomerular filtration rate (eGFR) greater than 90, 60-89, 45-59, and 30-44. Conversely, metformin use was associated with a higher risk of acidosis in patients with eGFR less than 30 (adjusted hazard ratio, 2.07; 95% confidence interval, 1.33-3.22). Metformin not increasing the risk of acidosis at eGFR greater than 30 also was noted in an additional analysis using sulfonylurea medications as an active comparator and was replicated in a separate database with 82,000 patients from 350 private health systems. As with all observational studies, this study is limited by the potential for residual confounding.
Bottom line: Metformin appears to be safe in CKD patients with eGFR above 30 mL/min per 1.73 m2.
Citation: Lazarus B et al. Association of metformin use with risk of lactic acidosis across the range of kidney function: A community- based cohort study.
Dr. Wanner is director, hospital medicine section, and associate chief, division of general internal medicine, University of Utah, Salt Lake City.