Unleash metformin: reconsideration of the contraindication in patients with renal impairment.

OBJECTIVE: To evaluate the expanded use of metformin in renal impairment. DATA SOURCES: The MEDLINE database via PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health were searched in August 2013 and included studies from 1950 onward. STUDY SELECTION AND DATA EXTRACTION: The search included comparative trials, observational cohort studies, and meta-analyses using the terms diabetes mellitus, metformin, renal insufficiency, and acidosis, lactic. DATA SYNTHESIS: One randomized controlled trial, 1 meta-analysis, 1 case-control, and 3 prospective-cohort studies, representing about 150 000 patients, revealed that metformin is safe in patients with stable mild-moderate renal impairment. The incidence of lactic acidosis is low and similar to sulfonylureas. In addition, reduced risks of cardiovascular disease, all-cause mortality, or any acidosis/serious infection were seen with metformin use in mild-to-moderate renal impairment.
CONCLUSIONS: Data over the past decade refute the historical contraindication in patients with renal impairment and suggest that the risk of metformin-associated lactic acidosis is low in stable mild-to-moderate renal impairment and similar to the risk with other type 2 diabetes mellitus (DM2) medications with no renal impairment restrictions. Because of its unique impact on microvascular and macrovascular complications, it is advantageous to utilize metformin as the cornerstone in DM2 treatment for as long as possible, including in those patients with mild to moderate stages of renal impairment with no additional contraindications. A dosage reduction is recommended if estimated glomerular filtration rate (eGFR) is between 30 and 45 mL/min/1.73 m(2) and discontinuation if eGFR is <30 mL/min/1.73 m(2).