Challenging the 4-h premedication regimen for iodinated contrast allergy: A multicenter retrospective study

The American College of Radiology (ACR) recommends an Accelerated 4-h intravenous (IV) premedication regimen (an antihistamine and a corticosteroid) for Emergency Department (ED) patients with documented iodinated contrast allergy who require contrast-enhanced computed tomography (CT). To test the validity of the ACR recommendation, we evaluated the association between the occurrence of any contrast reaction (mild, moderate, or severe) and the timing of contrast administration (≤ 4 vs > 4 h) among premedicated patients.

Retrospective cohort chart analysis across five EDs (January 2022-December 2024) of patients ≥21 years old with a documented iodinated contrast allergy, who received premedication before contrast-enhanced CT imaging. The primary outcome was the proportion of any contrast reaction (mild, moderate, or severe), as defined by the 2025 ACR Contrast Media Manual. Chi-square analysis was used to compare the reaction events in the 4-h premedication threshold groups.

347 subjects were included in the analysis, of whom 279 (80%) were in the ≤4 h group. Any contrast reaction occurred in 8 of 279 patients (3%) in the ≤ 4-h group as compared with 3 of 68 (4%) in the >4-h group (odds ratio, 0.66; 95% confidence interval, (0.17-2.5); p = 0.52). Of the 11 patients with contrast reactions, 6 were mild, 5 were moderate, and none were severe.

The occurrence of contrast-related breakthrough reactions was not significantly higher among patients who received iodinated contrast following IV premedication in ≤ 4 h. There were no mortalities in either the ≤ 4-h or the >4-h groups.