Cautions in use of contrast agents

Use of iodine contrast agents is contraindicated in pregnancy because they can cross the placenta and interfere with foetal thyroid development. 

Special precautions should be taken in patients with known hypersensitivity to iodine and in those with other allergies, for example to foods or other drugs. Prophylactic corticosteroids, for example prednisolone, are recommended as premedication 12-18 hours prior to imaging in such high-risk patients. 

Contrast agents should also be used with caution in patients with epilepsy because they can provoke seizures in hepato-renal syndrome (renal failure following liver cirrhosis and jaundice) in severe respiratory disease, especially asthma and in diabetes. 

Iodine contrast agents interact with metformin, an oral hypoglycaemic drug used to treat type 2 diabetes (see Chapter 6). Iodine contrast agents increase the risk of a patient developing lactic acidosis with metformin, particularly if their kidney function is impaired. Metformin has to be stopped prior to radiological examination and should not be restarted until normal renal function has resumed. 

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