Five types of oral antihyperglycemic drugs are currently approved for the treatment of diabetes: biguanides, sulfonylureas, meglitinides, glitazones, and alpha-glucosidase inhibitors. The cardiovascular effects of the most commonly used antidiabetic drugs in these groups are briefly reported, in an attempt to improve knowledge and awareness regarding their influences and potential risks when treating patients with coronary artery disease (CAD). Regarding biguanides, gastrointestinal disturbances such as diarrhea are frequent, and the intestinal absorption of group B vitamins and especially folate is impaired during chronic therapy. This deficiency may lead to increased plasma homocysteine levels which, in turn, accelerate the progression of vascular disease due to adverse effects on platelets, clotting factors, and endothelium. The existence of a graded association between homocysteine levels and overall mortality in patients with CAD is well established. In addition, metformin may lead to lethal lactic acidosis, especially in patients with clinical conditions that predispose to this complication, such as heart failure or recent myocardial infarction. Sulfonylureas avoid ischemic preconditioning. During myocardial ischemia, they may prevent the opening of the ATP-dependent potassium channels, impeding the necessary hyperpolarization that protects the cell by blocking calcium influx. Meglitinides may exert similar effects, due to their analogous mechanism of action. During treatment with glitazones, edema has been reported in 5% of patients, and these drugs are contraindicated in diabetics with NYHA class III or IV cardiac status. The long-term effects of a-glucosidase inhibitors on morbidity and mortality rates and on diabetic micro- and macrovascular complications are yet unknown. The combined sulfonylurea/metformin therapy reveals additive effects on mortality. It is concluded that (1) four of the five oral antidiabetic drug groups present proven or potential cardiac hazards; (2) these hazards are not mere "side effects", but are deeply rooted in the drugs' mechanism of action; (3) current data indicate that the combined glibenclamide/ metformin therapy seems to present special risk and should be avoided in the long-term management of type 2 diabetics with proven CAD; and (4) customized antihyperglycemic pharmacological approaches should be investigated for optimal treatment of diabetic patients with heart disease.
