Injected iodinated radiographic contrast media is generally safe, however with increased use adverse events are more likely to occur. In the latest edition of Australian Prescriber Kenneth Thomson, Professor and Director of Radiology, and Dinesh Varma, Head of Trauma and Emergency Radiology, at The Alfred in Melbourne, consider the indications for contrast media.

“Iodised contrast media are helpful in differentiating between normal and pathological areas. Common indications for contrast media include inflammatory, infective or neoplastic conditions,” the authors write.

However, they warn that intravenous contrast is only indicated when the contrast will add diagnostic value. A non-contrast scan or an alternative imaging investigation may provide sufficient diagnostic information. This is particularly important in patients with impaired renal function.

All patients should be assessed to see if they are at risk of an adverse reaction to contrast media, the authors say.

“The most important adverse effects include hypersensitivity reactions, contrast-induced nephropathy and thyrotoxicosis. There is no protocol that will prevent non-IgE-mediated anaphylaxis. In patients with moderate renal dysfunction, adequate hydration and use of as little contrast media as practical is recommended."

The authors also warn about an association between metformin and several cases of renal failure and lactic acidosis in patients who have received contrast media.

“If contrast media causes renal failure, metformin, which is renally excreted, can reach toxic levels resulting in lactic acidosis. It is now recommended that metformin be discontinued at least 12 hours before the contrast investigation and not be resumed for a minimum of 36 hours after the procedure, and longer if the serum creatinine has not returned to baseline,” they advise.

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ENDS

Australian Prescriber is an independent peer-reviewed journal providing critical commentary on therapeutic topics for health professionals, particularly doctors in general practice. It is published by National Prescribing Service Limited (NPS), an independent, non-profit organisation for Quality Use of Medicines funded by the Australian Government Department of Health and Ageing.