Metformin use and mortality in patients with advanced chronic kidney disease: National, retrospective, observational, cohort study

[[abstract]]BACKGROUND: Metformin is recommended as a first-line treatment for patients with type 2 diabetes. However, use of this drug has been contraindicated in individuals with impaired kidney function because of the perceived risk of lactic acidosis. Evidence now supports cautious use of metformin in people with mild-to-moderate chronic kidney disease. However, studies examining the use of metformin in patients with advanced chronic kidney disease are lacking. We aimed to assess the safety of metformin in patients with type 2 diabetes and advanced (approximately stage 5) chronic kidney disease. METHODS: We did a retrospective, observational, cohort study of patients with type 2 diabetes who were enrolled prospectively in Taiwan's national health insurance research database between Jan 1, 2000, and June 30, 2009, and had follow-up data until Dec 31, 2009. We included individuals with a serum creatinine concentration greater than 530 mumol/L, which is approximately equivalent to stage 5 chronic kidney disease. From a consecutive sample of 12 350 patients with type 2 diabetes and chronic kidney disease, 1005 used metformin and 11 345 were non-users. We matched users and non-users of metformin by propensity score in a 1:3 ratio. Our primary outcome was all-cause mortality. FINDINGS: 813 metformin users were matched by propensity score to 2439 non-users. The two groups of patients did not differ significantly by 30 baseline clinical and socioeconomic variables. Median follow-up in the matched cohort was 2.1 years (range 0.3-9.8). All-cause mortality was reported in 434 (53%) of 813 metformin users and in 1012 (41%) of 2439 non-users. After multivariate adjustment, metformin use was an independent risk factor for mortality (adjusted hazard ratio 1.35, 95% CI 1.20-1.51; p