Current understanding of contrast media reactions and implications for clinical management.

Iodinated contrast media (CM) are an integral part of modern diagnostic medicine. Although these agents are considered to be relatively safe, adverse effects in the form of allergy-like reactions occur in a significant number of exposed patients. These reactions may be divided into immediate and delayed responses. Immediate (within 1 hour of administration) anaphylactic reactions range from urticaria and angioedema to laryngeal oedema, hypotension and even death. Delayed reactions to CM occur from 1 hour to 1 week after administration and usually have mostly cutaneous manifestations. History of prior CM reactions and atopy predispose patients to CM reactions. Despite intense research into the pathogenesis of the immediate anaphylactoid responses, new evidence shows that true IgE type I hypersensitivity mediation occurs only in rare, severe cases. The aetiology appears to be multifactorial in most individuals. There is strong evidence to conclude that type IV hypersensitivity is responsible for the delayed reactions to CM. Although switching to non-ionic agents significantly reduces the incidence of immediate reactions to CM, there is little consensus regarding corticosteroid prophylaxis in high-risk individuals. Skin testing and provocative challenges also provide little security. Therefore, physicians must be better prepared to treat immediate anaphylactoid responses. Preventing delayed CM reactions is best performed with patch and delayed intradermal testing in those with a history of prior reactions, although false-negative results have been reported. Corticosteroids and antihistamines may be required for treatment. Until newer agents are developed that negate these issues, healthcare providers must strive to better understand the risk factors associated with CM reactions, as well as the available prophylactic and treatment options.