Metformin belongs to the Biguanide class of medications used to treat Type 2 Diabetes. Metformin works by decreasing the amount of glucose produced by the liver, improving insulin sensitivity, and by increasing cellular uptake of glucose.
In patients who develop acute or chronic renal failure, the clearance of metformin is decreased resulting in an increased risk of lactic acidosis, which may have a mortality rate up to 50%. Patients who receive IV contrast fluid are at risk for contrast-induced nephropathy and if they are concurrently on metformin, they may experience potentially fatal lactic acidosis. To avoid this issue, most patients scheduled to receive IV contrast have their metformin medication stopped at the time of contrast administration for at least 48 hours after the procedure.
In some patients who have preserved renal function and are receiving small amounts of contrast (< 100 mL), stopping the metformin may not be necessary because the risk of contrast-induced nephropathy is very low in these patients.