Acute renal failure from contrast medium

Editor—Mathew et al highlight the dangers of contrast induced nephropathy in a patient with type 2 diabetes mellitus.¹

Such patients are often treated with the biguanide metformin, which is excreted by the kidney. Even with normal renal function, metformin should be withheld for 48 hours from the time of the radiological study if intravenous iodinated contrast media is to be given, with close monitoring of renal function before restarting.² This is to prevent, in the context of contrast induced nephropathy, high serum metformin concentrations, which could lead to lactic acidosis. A review of published cases of metformin induced lactic acidosis shows that 8% occur in presence of contrast induced nephropathy.³ This risk increases in diabetic patients with preexisting renal impairment. With known renal impairment, metformin should be stopped 48 hours before the study, to allow monitoring of the renal function, and low osmolar contrast media should always be used.²

Remember also that patients with multiple myeloma have multiple risk factors for acute renal failure, including hypercalcaemia, dehydration, infection, and urinary light chains, and that contrast (particularly with older contrast agents) may be a further insult to the kidney.⁴