Metformin will be used in more diabetes patients with kidney disease as FDA labeling catches up with the evidence. We're used to avoiding metformin if serum creatinine is over 1.5 mg/dL for men or over 1.4 mg/dL in women due to fear of lactic acidosis. But lactic acidosis is EXTREMELY rare, even in kidney disease. And now labeling will base metformin dosing on estimated glomerular filtration rate (eGFR) not serum creatinine or creatinine clearance. Feel comfortable giving metformin for most patients with eGFR over 45 mL/min. But don't start it if eGFR is under 45 mL/min.
Monitor kidney function at least annually in metformin patients, and more often in those at higher kidney risk (elderly, taking an ACEI, etc). Keep in mind, the benefits of continuing metformin in most type 2 patients outweigh the risks even if eGFR falls to 30 to 45 mL/min. But stop metformin if eGFR drops BELOW 30 mL/min.
Continue to start with 500 mg/day of metformin and titrate by 250 or 500 mg every 1 to 2 weeks as tolerated. Aim for a target dose of 2 g/day in most patients. New labeling doesn't suggest adjusting the metformin dose based on kidney function. Consider if metformin may now be appropriate in type 2 patients with kidney disease to possibly improve outcomes and meet quality measures.
REFERENCES
Inzucchi SE, Lipska KJ, Mayo H, Bailey CJ, McGuire DK. Metformin in patients with type 2 diabetes and kidney disease: a systematic review. JAMA. 2014 Dec 24-31;312(24):2668-75. Available at: https://pubmed.ncbi.nlm.nih.gov/25536258
FDA. GLUCOPHAGE (metformin hydrochloride). [online] Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/020357s037s039,021202s021s023lbl.pdf