Metformin use and mortality in ambulatory patients with diabetes and heart failure.

BACKGROUND Despite the common coexistence of diabetes and heart failure (HF), the optimal medial treatment of diabetes in HF patients has not been well studied. We sought to compare the association between metformin use and clinical outcomes in a cohort of ambulatory patients with diabetes and established HF. METHODS AND RESULTS Using propensity score-matched samples, we examined the association between metformin use and the risk of death or risk of hospitalization in a national cohort of 6185 patients with HF and diabetes treated in ambulatory clinics at Veteran Affairs medical centers. In this cohort, 1561 (25.2%) patients were treated with metformin. At 2 years of follow-up, death occurred in 246 (15.8%) patients receiving metformin and in 1177 (25.5%) patients not receiving metformin (P<0.001). In the propensity score-matched analysis (n=2874), death occurred in 232 (16.1%) patients receiving metformin compared with 285 (19.8%) patients not receiving metformin (hazard ratio, 0.76; 95% confidence interval, 0.63 to 0.92; P<0.01). In propensity score-matched analyses, HF hospitalization or total hospitalization rates were not significantly different between individuals treated with metformin compared with those not treated with metformin (hazard ratio, 0.93; 95% confidence interval, 0.74 to 1.18; and hazard ratio, 0.94; 95% confidence interval, 0.83 to 1.07, respectively). CONCLUSIONS Metformin therapy was associated with lower rates of mortality in ambulatory patients with diabetes and HF. Future prospective studies are necessary to define the optimal therapy for diabetic patients with HF.