Preventive Effect of Changing Contrast Media in Patients With A Prior Mild Immediate Hypersensitivity Reaction to Gadolinium-Based Contrast Agent Objectives Currently, the prevention of recurrent immediate hypersensitivity reactions (HSRs) to contrast media (CM) requests premedication and changing the culprit contrast agent. However, strategies for the prevention of immediate HSRs to gadolinium-based magnetic resonance contrast agents (GBCAs) have not yet been established. This study aimed to evaluate the effectiveness of changing the contrast agent and single-dose premedication for HSR recurrence prevention in patients with a history of mild immediate HSR to GBCA. Materials and Methods The outcomes of patients with mild immediate HSR to GBCA who subsequently underwent enhanced magnetic resonance imaging between October 2012 and July 2017 were analyzed. The institutional CM monitoring system was retrospectively reviewed, and data on the application of premedication and choice of CM were obtained. Gadolinium-based magnetic resonance contrast agents were classified into 3 classes according to their molecular structure (macrocyclic ionic, macrocyclic nonionic, and linear ionic). Intravenous chlorpheniramine 4 mg, 30 minutes before the GBCA administration, or intravenous methylprednisolone sodium succinate 40 mg plus chlorpheniramine 4 mg, 1 hour before the GBCA administration, was administrated as premedication regimen. Recurrence rates of immediate HSR were compared according to prevention strategies. Results A total of 185 patients with a history of mild immediate HSR to GBCA were re-exposed to GBCA 397 times during the study period. The overall recurrence rate was 19.6% (78/397). Changing the culprit GBCA significantly reduced the recurrence rate, compared with reusing the culprit GBCA (6.9%, 9/130 and 25.8%, 69/267; P < 0.001). The recurrence rate was lowest when the GBCA was changed to a different molecular structure class from the culprit agent, followed by changing to CM with the same molecular structure and reusing the culprit GBCA (6.2%, 7/113 vs 11.8%, 2/17 vs 25.8%, 69/267; P < 0.001 with χ2 test for trend). Single-dose premedication demonstrated no significant prophylactic effect on recurrence (20.4%, 17/98 vs 17.3%, 61/299 with and without premedication, respectively; P = 0.509). Premedication in addition to changing CM also showed no additional prophylactic effect (7.2%, 7/97 and 6.1%, 2/33, respectively; P = 0.821). Conclusions Changing the CM from the culprit agent could reduce the chance of HSR recurrence in patients with prior mild immediate HSR to GBCA, especially when the CM was changed to one of a different molecular structure class. However, single-dose premedication administration did not show significant HSR recurrence rate difference. Received for publication January 29, 2019; and accepted for publication, after revision, March 20, 2019. The authors report no conflicts of interest. Correspondence to: Young Hun Choi, MD, Department of Radiology, Seoul National University Hospital, 101 Daehak-ro, Jongno-gu, Seoul 03080, South Korea. E-mail: iater@snu.ac.kr. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.