Metformin: safety in cardiac patients.

Metformin is a biguanide, insulin sensitiser that reduces blood sugar levels. There are concerns about the risk of lactic acidosis in patients receiving metformin who have procedures requiring iodinated contrast, and in those with renal impairment or heart failure. The data on which these concerns are based are reviewed, with the conclusion that metformin treatment is rarely to blame for lactic acidosis. A generic policy of stopping metformin 48 h before and 48 h after the procedure in all patients is counterintuitive, lacks any evidence base and does not conform to the principles of best practice. In patients with heart failure, although the underlying condition can predispose to lactic acidosis, existing evidence suggests that metformin use is associated with improved outcome rather than increased risk.