Delayed allergy-like reactions to X-ray contrast media: mechanistic considerations

Iodinated X-ray contrast media are among the most frequently used pharmaceu ticals for intravascular administration. Although the newer low osmolality, nonionic contrast media, are generally well tolerated it is well known tha t they, like the ionic contrast. give rise to immediate or delayed adverse reactions in susceptible individuals. In the present review delayed allergy -like reactions, which by definition occur more than 1 h after contrast med ium administration ,are described, and the possible patho-physiological mec hanisms discussed. Delayed allergy-like reactions to contrast media which h ave been media, which have been reported to occur in 0.5-2 % of recipients, are mainly mild to modern skin reactions of the maculopapular exanthematou s and urticaril/angioedematous types. Most of the reactions become apparent after a latency of 3 h to 2 days and dissappear within 1 week. The inciden ce of more severe reactions is extremely low. Main risk factors for delayed allergy-like reactions appear to be a previous contrast medium reaction, a history of allergy, IL-2 treatment and being of Japanese descent. At prese nt, the exact pathogenesis of these delayed reactions is still unclear. The re is, however, increasing evidence that a significant proportion of the re actions are T- cell mediated.