Abstract
Patients with a history of anaphylactoid reaction to radiographic contrast medium (RCM) are at increased risk for subsequent reaction. Of these high-risk patients 275 were studied with use of prophylactic pretreatment with diphenhydramine hydrochloride or prednisone or both without a single severe anaphylactoid reaction on readministration of RCM. A patient who received pretreatment as described but suffered a life-threatening anaphylactoid reaction on readministration of RCM is described. Premedication does not eliminate the possibility of a fatal reaction on readministration of RCM.