Reactions to iodinated contrast media range from mild inconvenience to life-threatening emergency. Histamine release can account for many of the symptoms and nonionic agents are tolerated better than ionics. Reactions can be immediate (IR) or delayed (DR). Incidences of the former are 3–4 % (ionics), 0.2–0.7 % (non-ionics), severe reactions 0.1–0.4 % (ionics), and 0.02–0.04 % (non-ionics). Up to 80 % of reactions can be avoided by using nonionic agents. For DRs, there is no difference between the incidences of reactions to each of the agents. Risk factors for IRs are a previous reaction to a contrast medium, bronchial asthma, cardiac disease, and highly allergic subjects; for DRs, a previous reaction, use of β-blockers, treatment with IL-2, history of drug allergy, and contact allergy. Diagnosis of IRs is based largely on skin tests; IgE antibodies have not been convincingly demonstrated. Breakthrough reactions have occurred following corticosteroid and H1 antagonist premedication. Gadolinium-based agents, especially the linear chelates, have been associated with nephrogenic systemic fibrosis. They show an adverse reaction incidence of about 0.48 % and 0.01 % for anaphylaxis. Overall, given the large number of contrast media administered, they are one of the safest drugs.
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