[Metformin and insulin in chronic heart failure: contraindications not contraindicated and indications not indicated]

Glucose-lowering treatment in patients with type 2 diabetes and heart failure is controversial. Metformin is clearly contraindicated when such diseases coexist. Conversely, no contraindications have been established for insulin in this subset of patients, even though several observational and retrospective studies have shown increased mortality and worsening heart failure. Data from the literature have demonstrated that in this patient population, which accounts for one third of all cases of heart failure, metformin reduces mortality by 14-35%. In patients with a glomerular filtration rate >30 ml/min who do not show dehydration, shock, sepsis, severe liver disease or hypoxemia, the administration of metformin doses <2 g/day was associated with a null risk of lactic acidosis. The positive effects of metformin are correlated with the reduction in insulin resistance, which is responsible for both the onset and development of heart failure in diabetic patients. Insulin can provoke severe hypoglycemia and fluid retention, resulting in negative effects. Further randomized and prospective studies are warranted to address these controversial issues in such a large population with high mortality and morbidity rates. Longitudinal studies would be crucial to the understanding of the optimal therapy and for stratification of patients according to the severity of heart failure.