Is metformin beneficial for heart failure in patients with type 2 diabetes?

Heart failure is a common and serious cardiovascular complication of type 2 diabetes. Many antihyperglycemic drugs can increase the risk of heart failure. However, it is commonly believed that metformin - the first-line treatment for type 2 diabetes - reduces the risk of and improves the clinical course of heart failure. It is estimated that 20-25% of patients taking metformin have heart failure. Metformin has been shown to have favorable effects on the course of heart failure in experimental models. Furthermore, when compared with other antihyperglycemic medications in nonrandomized epidemiological studies, metformin users had a lower risk of new-onset heart failure and a lower risk of death if they already had heart failure. However, these reports are difficult to interpret, given the potential for prescribing bias and the likelihood that comparator agents caused cardiovascular harm. Meta-analyses of randomized controlled clinical trials have not demonstrated benefits of metformin on the risk of or the clinical course of heart failure. Given metformin's importance in the management of type 2 diabetes and its widespread use in heart failure, the current confidence in its benefits in high-risk patients needs to be re-evaluated.