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The authors thank Smitha John for summarizing the benefits of metformin as an inexpensive and effective antidiabetic agent with a low risk of hypoglycemia that has been shown to reduce macrovascular events and mortality. For these reasons, the American Diabetes Association recommends metformin as a first-line agent for the treatment of type-2 diabetes.1American Diabetes Association Approaches to glycemic treatment.Diabetes Care. 2016; 39: S52-S59Google Scholar Based on the available evidence for low risk of lactic acidosis in the presence of mild-to-moderate impairment assessed by estimated glomerular filtration rate (eGFR), John concurs with the use of metformin in patients with type 2 diabetes and eGFR rate levels between 30 and 60 mL/min/1.73 m2, as summarized in our article in the February 2016 issue of The American Journal of Medicine.2Vassalotti J.A. Centor R. Turner B.J. et al.A practical approach to detection and management of chronic kidney disease for the primary care clinician.Am J Med. 2015; 129: 153-162Abstract Full Text Full Text PDF Scopus (123) Google Scholar Your letter is timely because, on April 8, 2016, the US Food and Drug Administration (FDA) published a nearly identical guidance in the Drug Safety Communication: FDA revises warnings about use of the diabetes medicine metformin in certain patients with reduced kidney function.3US Food and Drug Administration (FDA). FDA Drug Safety Communication: FDA revises warnings regarding use of the diabetes medicine metformin in certain patients with reduced kidney function. 2016, Available at: http://www.fda.gov/downloads/Drugs/DrugSafety/UCM494140.pdf. Accessed April 13, 2016.Google Scholar The former black box warning to avoid metformin when the serum creatinine is ≥1.5 mg/dL in men and 1.4 mg/dL in women, owing to the risk of lactic acidosis, is replaced by the criteria shown in the Table. The FDA and John concur with us that decisions about prescribing metformin need to be based on eGFR, which is more accurate than serum creatinine alone.TableLabeling Revisions for FDA-Approved Metformin-Containing Medicines3US Food and Drug Administration (FDA). FDA Drug Safety Communication: FDA revises warnings regarding use of the diabetes medicine metformin in certain patients with reduced kidney function. 2016, Available at: http://www.fda.gov/downloads/Drugs/DrugSafety/UCM494140.pdf. Accessed April 13, 2016.Google ScholarPrior to starting metformin, obtain the patient's eGFR.Metformin is contraindicated in patients with an eGFR below 30 mL/min/1.73 m2.Starting metformin in patients with an eGFR between 30 and 45 mL/min/1.73 m2 is not recommended.Obtain an eGFR at least annually in all patients taking metformin. In patients at increased risk for the development of renal impairment such as the elderly, renal function should be assessed more frequently.In patients taking metformin whose eGFR later falls below 45 mL/min/1.73 m2, assess the benefits and risks of continuing treatment. Discontinue metformin if the patient's eGFR later falls below 30 mL/min/1.73 m2.Discontinue metformin at the time of or prior to an iodinated contrast imaging procedure in patients with an eGFR between 30 and 60 mL/min/1.73 m2; in patients with a history of liver disease, alcoholism, or heart failure; or in patients who will be administered intra-arterial iodinated contrast. Re-evaluate eGFR 48 hours after the imaging procedure; restart metformin if renal function is stable.eGFR = estimated glomerular filtration rate; FDA = US Food and Drug Administration. Open table in a new tab eGFR = estimated glomerular filtration rate; FDA = US Food and Drug Administration. Metformin in Chronic Kidney Disease – Should We Worry?The American Journal of MedicineVol. 129Issue 9PreviewI had the opportunity to read the article “Practical Approach to Detection and Management of Chronic Kidney Disease for the Primary Care Clinician” by Joseph A. Vassalotti et al, in the September 2015 online edition of The American Journal of Medicine. I would like to commend the authors on this very informative article and, at the same time, emphasize a very valid point made in the article with regards to utilizing estimated glomerular filtration rate (eGFR) to guide the use of metformin in chronic kidney disease. Full-Text PDF