Potential impact of prescribing metformin according to EGFR rather than serum creatinine

Abstract

OBJECTIVE Many societies recommend using estimated glomerular filtration rate (EGFR) rather than serum creatinine (sCr) to determine metformin eligibility. We examined the potential impact of these recommendations on metformin eligibility among U.S. adults. RESEARCH DESIGN AND METHODS Metformin eligibility was assessed among 3,902 adults with diabetes who participated in the 1999-2010 National Health and Nutrition Examination Surveys and reported routine access to health care, using conventional sCr thresholds (eligible if <1.4 mg/dL for women and <1.5 mg/dL for men) and EGFR categories: likely safe, ≥=;45 mL/min/1.73 m2; contraindicated, <30 mL/min/1.73 m2; and indeterminate, 30-44 mL/min/1.73 m2). Different EGFR equations were used: four-variable MDRD, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine (CKD-EPIcr), and CKD-EPI cystatin C, as well as Cockcroft-Gault (CG) to estimate creatinine clearance (CrCl). Diabetes was defined by self-report or A1C ≥6.5% (48 mmol/mol). We used logistic regression to identify populations forwhommetforminwas likely safe adjusted for age, race/ethnicity, and sex. Results were weighted to the U.S. adult population. RESULTS Among adultswith sCr above conventional cutoffs,MDRDEGFR ≥45 mL/min/1.73m2 wasmost commonamongmen (adjusted odds ratio [aOR] 33.3 [95%CI 7.4-151.5] vs. women) and non-Hispanic Blacks (aOR vs. whites 14.8 [4.27-51.7]). No individuals with sCr below conventional cutoffs had an MDRD EGFR <30 mL/min/1.73 m2. All estimating equations expanded the population of individuals for whommetformin is likely safe, ranging from 86,900 (CKD-EPIcr) to 834,800 (CG). All equations identified larger populations with EGFR 30-44mL/min/1.73 m2, for whom metformin safety is indeterminate, ranging from 784,700 (CKD-EPIcr) to 1,636,000 (CG). CONCLUSIONS The use of EGFR or CrCl to determine metformin eligibility instead of sCr can expand the adult population with diabetes for whom metformin is likely safe, particularly among non-Hispanic blacks and men.