Hypersensitivity reactions to radio-contrast media (RCM) during radiological investigations are generally divided into immediate-type reactions, occurring within 1 h, and delayed reactions, occurring typically at 6-12h. Cross-reactivity between different RCM is more commonly found with delayed reactions, suggesting a common moiety and mechanism. In the past, adverse reactions were much more common after the administration of ionic high osmolar contrast media, and the incidence of these reactions declined significantly after they were replaced by non-ionic low-osmolar agents. However, the number of reactions seen in clinical practice has remained significant because of the increasing use of radiological investigations involving contrast. In the United Kingdom, the management of adverse reactions to RCM has remained the domain of radiologists.
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