Breakthrough allergic-like reactions to contrast media despite preventive measures in patients with prior reactions: A retrospective study

Abstract

Background: Breakthrough allergic-like reaction (BTR) to iodinated contrast media, an allergic-like reaction despite premedication and contrast switching, remains an important safety concern.

Objective: To determine BTR incidence and identify its predictors, particularly whether contrast group membership and side-chain similarity are associated with reaction risk.

Methods: A retrospective cohort study of iodinated contrast media administration with premedication in patients with prior allergic-like reactions at Bangkok Metropolitan Administration General Hospital (September 2015–December 2025). The primary outcome was BTR incidence. Contrast administration was classified into three categories: 1) different group, different side chain; 2) different group, similar side chain; and 3) same group, same side chain. Generalized estimating equations (GEE) was used to account for multiple exposures per patient.

Results: A total of 572 contrast administrations from 210 patients were included; BTR occurred in 55 (9.6%, 95% CI 7.20%–12.03%). Independent predictors in the GEE model included same contrast group (OR 2.52, 95% CI 1.11–5.69, P = 0.027), female sex (OR 2.03, 95% CI 1.06–3.88, P = 0.032), younger age (OR 0.97 per year, 95% CI 0.94–0.99, P = 0.019), and first rechallenge exposure (OR 2.45, 95% CI 1.33–4.52, P = 0.004). Differentgroup switching with similar side chains was not independently associated with BTR.

Conclusion: BTR occurred in 9.6% of premedicated re-exposures. An alternative agent from the same contrast group was the most important modifiable predictor, while side-chain similarity alone did not significantly increase risk. This supports prioritizing contrast group switching when choosing an alternative agent.