• Chin-Chi Kuo, Hung-Chieh Yeh, Bradley Chen, Ching-Wei Tsai, Yu-Sheng Lin, and Chiu-Ching Huang.
• From the Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health (C-CK); Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health (C-CK); Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, Baltimore, MD (C-CK); Department of Internal Medicine, Kidney Institute and Division of Nephrology, China Medical University Hospital and College of Medicine, China Medical University, Taichung (C-CK, H-CY, C-WT, C-CH); Institute of Public Health, National Yang-Ming University, Taipei, Taiwan (BC); and Department of Environmental and Occupational Health, University of North Texas Health Science Center, Fort Worth, TX (Y-SL).
• Medicine (Baltimore). 2015 Dec 1; 94 (51): e2175e2175.

AbstractThe use of metformin in chronic kidney disease (CKD) population has been intensely debated with conflicting evidence. Large population studies are needed to inform risk assessment and therapeutic decision-making. We evaluated the associations among metformin, metabolic acidosis, and CKD in a 10-year nationally representative noninstitutionalized civilian population in the United States.In this cross-sectional study, a total of 2279 diabetic adults aged 20 years or older in the National Health and Nutrition Examination Survey (NHANES) from 2003 to 2012 were included and had measurements of serum bicarbonate, sodium, potassium, and chloride. The exposure was metformin use. The outcome was subclinical and severe metabolic acidosis defined by serum bicarbonate <23 mEq/L and anion gap > 16mEq/L and by serum bicarbonate < 20 mEq/L, respectively.The prevalence of metformin use decreased from 67.2% among CKD-1 and -2, 40.6% among CKD-3, to 1.3% among advanced CKD-4 and -5. Across CKD stages up to CKD-3b, we observed a tendency of lower levels of serum bicarbonate that was significant in metformin users with CKD-2 and CKD-3a and marginally significant with CKD-3b compared to nonmetformin users. The corresponding tendency of higher anion gap in metformin users with the estimated glomerular filtration rate >60 mL/min/1.73 m was also observed. In multiple linear regression analysis, metformin was significantly associated with decreased serum bicarbonate levels (β = -0.45, 95% CI: -0.73, -0.17) and increased serum anion gap levels (β = 0.40, 95% CI: 0.19, 0.61). The adjusted odds ratio of subclinical high anion gap and severe metabolic acidosis for metformin users was 1.68 (95% CI: 1.11, 2.55) and 1.31 (0.49, 3.47), respectively. The association between metformin and serum bicarbonate was significantly modified by CKD status. No interaction was found between metformin and CKD stages for serum anion gap and acidosis.Metformin is associated with subclinical metabolic acidosis but not with severe metabolic acidosis. The propensity of serum bicarbonate-lowering effect was intensified in advanced CKD; however, such tendency was not associated with the risk of clinically defined acidosis. Our findings highlight a potential of cautious expansion of metformin use among CKD-3b patients with diabetes meriting further investigations.

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