PREVENTION OF ANAPHYLACTOID REACTIONS IN HIGH-RISK PATIENTS RECEIVINGRADIOGRAPHIC CONTRAST-MEDIA

OBJECTIVE: To review various pretreatment regimens for the prophylaxis of anaphylactoid reactions to radiographic contrast media (RCM) in hi gh-risk patients. The proposed etiologies and risk factors for such re actions are also reviewed. DATA SOURCES: A MEDLINE search of the Engli sh-language literature was used to identify pertinent human studies an d reviews. STUDY SELECTION: All studies comparing pretreatment regimen s for anaphylactoid reactions to RCM were reviewed as well as studies comparing the incidence of anaphylactoid reactions between lower and h igher osmolar RCM. DATA SYNTHESIS: The two types of reactions to RCM a re the dose-independent, unpredictable anaphylactoid (pseudoallergic o r idiosyncratic) reactions and the dose-dependent, predictable physico chemical (intrinsic, nonidiosyncratic) reactions. Prophylaxis of the f ormer type is targeted at stemming the effects of certain chemical med iators, primarily histamine. The use of lower osmolar RCM is associate d with a lower incidence of anaphylactoid reactions compared with high er osmolar RCM, but is significantly more expensive. Risk factors for such reactions are a history of previous anaphylactoid reaction to RCM , asthma, and reaction to skin allergens or penicillin. Discontinuatio n of any beta-blockers before the procedure is suggested. Pretesting p atients with a small amount of RCM has little predictive value for an anaphylactoid reaction. Various pretreatment prophylactic regimens hav e been studied. Almost all included a corticosteroid to target the inf lammatory response and a histamine, (H-1)-antagonist to blunt the effe cts of histamine. In some clinical trials, ephedrine was added for bro nchodilation and cimetidine for its antagonism at die histamine2-recep tor. The few controlled clinical trials that have been performed show the combination of prednisone and diphenhydramine to be most beneficia l in preventing anaphylactoid reactions to RCM. The addition of ephedr ine or cimetidine to a pretreatment regimen remains controversial. CON CLUSIONS: More controlled clinical studies comparing various pretreatm ent regimens for high-risk patients need to be performed, especially i n patients receiving lower osmolar RCM. Recommendations for high-risk patients who must receive RCM include use of a lower osmolar agent, pr etreatment with a corticosteroid and an H-1-antagonist, discontinuatio n of beta-blockers if the patient is taking any, and bedside availabil ity of appropriate medications and equipment to treat anaphylaxis.