REACTIONS TO IODINE-BASED CONTRAST-MEDIA

Contrast media are used in many radiological examinations, but they are responsible for 4.6 to 8.5 percent of the toxic or anaphylactoid adverse reactions observed. The early contrast media were hyperosmolar, whereas those in current use are isoosmolar and either ionic or non-ionic. The patient's age, the presence of a pre-existing disease and a history of adverse reactions to contrast media are the most important risk factors. Seventeen to 35 percent of these reactions recur. Several physiopathological mechanisms have been blamed for adverse reactions to contrast media, including complement activation, histamine release, recruitment of inflammation mediators, and antigen-antibody reaction. There is no paraclinical examination that can diagnose or predict such reactions. Various preventive tests have been studied and applied to individuals with or without history of reaction. In a population of patients with previous reaction, the administration of corticosteroids 12 h and 2 h before the radiological examination resulted in a significant reduction of the number of reactions. In patients at risk (i.e. those with previous reactions of this kind) the results varied, but in these 2 groups of subjects non-ionic products given either alone or with corticosteroids or H1-antihistaminics reduced to 1 percent the incidence of reactions. So far, tachyphylaxis has virtually played no role compared with these preventive treatments. It is concluded that patients with a history of anaphylactoid reactions who must receive another injection of contrast medium, a non-ionic product and/or the H1-antihistaminic-corticosteroid combination should be used.