Study Overview
Objective. To assess whether metformin use is associated with lower risk of fatal or nonfatal major adverse cardiovascular events (MACE) as compared to sulfonylurea use among diabetic patients with reduced kidney function.
Design. Retrospective cohort study of US Veterans receiving care within the Veterans Health Administration, with data supplemented by linkage to Medicare, Medicaid, and National Death Index data from 2001 through 2016.
Setting and participants. A retrospective cohort of Veterans Health Administration (VHA) patients, aged 18 years and older. Pharmacy data included medication, date filled, days supplied, and number of pills dispensed. For Medicare and Medicaid patients, enrollees’ claims files and prescription (Part D) data were obtained. In addition, dates and cause of death were obtained from vital status and the National Death Index files.
Patients with new-onset type 2 diabetes were identified by selecting new users of metformin, glipizide, glyburide, or glimepiride. These patients were followed longitudinally and the date of cohort entry and start of follow-up was the day of reaching a reduced kidney function threshold, defined as either an estimated glomerular filtration rate (eGFR) of less than 60 mL/min/1.73 m2 or serum creatinine level of 1.5 mg/dL for men or 1.4 mg/dL for women. Patients were excluded for nonpersistence, defined as 90 days without an antidiabetic drug; censoring, defined as the 181st day of no VHA contact; or study end date of December 31, 2016.
Main outcome measures. Primary outcome was the composite of MACE including hospitalization for acute myocardial infarction (AMI), ischemic or hemorrhagic stroke, transient ischemic attack (TIA), or date of cardiovascular death. The secondary outcome excluded TIA as part of the composite MACE event because not all patients who sustain a TIA are admitted to the hospital.
Main results. From January 1, 2002 through December 30, 2015, 67,749 new metformin users and 28,976 new sulfonylurea users who persisted with treatment were identified. After using propensity score-weighted matching, 24,679 metformin users and 24,799 sulfonylurea users entered the final analysis. Cohort patients were 98% male and 81.8% white. Metformin users were younger than sulfonylurea users, with a median age of 61 years versus 71 years, respectively.
For the main outcome, there were 1048 composite MACE events among metformin patients with reduced kidney function and 1394 MACE events among sulfonylurea patients, yielding 23.0 (95% confidence interval [CI], 21.7-24.4) versus 29.2 (95% CI, 27.7-30.7) events per 1000 person-years of use, respectively, after propensity score-weighting. After covariate adjustment, the cause-specific adjusted hazard ratio (aHR) for MACE was 0.80 (95% CI, 0.75-0.86) among metformin users compared with sulfonylurea users. The adjusted incidence rate difference was 5.8 (95% CI, 4.1-7.3) fewer events per 1000-person years for metformin compared with sulfonylurea users. Results were also consistent for each component of the primary outcome, including cardiovascular hospitalizations (aHR, 0.87; 95% CI, 0.80-0.95) and cardiovascular deaths (aHR, 0.70; 95% CI, 0.63-0.78).