Hypersensitivity Reactions to Iodinated Radiocontrast Media

Abstract

Radio contrast media (RCM) are among the most common elicitors of drug hypersensitivity reactions due to their increasing use in iodinated X-ray images and computed tomography. Immediate hypersensitivity reactions (≤1 h after exposure) to RCM may lead to urticaria or anaphylaxis, and delayed hypersensitivity reactions (>1 h after exposure) typically present as maculopapular exanthems. The reaction is directed normally against the different RCM benzene ring molecules to which three iodine atoms are attached and not to the iodine ion. Evidence for an immunologic mechanism in RCM hypersensitivity reactions and the benefit of allergological testing is increasing. Positive skin tests have been used to confirm allergy in patients with previous reactions to RCM and in patients with positive skin tests, negative results are useful in the selection of an alternative RCM to be use in the future. Severe hypersensitivity reactions appear to be more likely caused by an allergic mechanism and skin testing is more likely to be positive and hence highly recommended in such reactions. On the other hand, the majority of patients with mild to moderate immediate hypersensitivity reactions do not exhibit positive skin tests results. If RCM are required again, structurally different, skin test-negative preparations should be applied. Changing to a structurally different RCM has been reported to be more effective than premedication to prevent future reactions. Drug provocation tests to RCM have been increasingly used to demonstrate tolerability of alternative RCMs or to exclude RCM hypersensitivity.