Transient refractory period in severe iodinated contrast media allergy: a case report

Dungan, L., Cox, F.  Allergy Asthma Clin Immunol 21, 43 (2025). https://doi.org/10.1186/s13223-025-00972-5

Abstract

Background

Hypersensitivity reactions to iodinated contrast media (ICM) are rare but can be life-threatening. Management typically involves avoidance of the offending agent and the use of alternative imaging strategies. The phenomenon of a transient refractory period—wherein a patient does not exhibit an allergic response upon re-exposure to the allergen shortly after an initial reaction—has been proposed but is not well-documented in the context of ICM.

Case presentation

Serum Tryptase versus Time from Anaphylaxis Episode. Purple arrows
represent the two time points at which iodinated contrast media was
administered.

We report the case of a 56-year-old woman who experienced an anaphylaxis associated cardiac arrest following administration of iopamidol 370 (Niopam 370) during a computed tomography pulmonary angiogram (CTPA). She was resuscitated, intubated, and stabilized with noradrenaline. Two hours later, she underwent a second CT scan using iopamidol 300 (Niopam 300) without any obvious immediate hypersensitivity reaction.

Subsequent skin testing was positive for both Niopam 370 and Niopam 300, but negative for alternative agents - iodixanol (Visipaque) and iohexol (Omnipaque).

Conclusions

This case suggests the presence of a transient refractory period following a severe hypersensitivity reaction to ICM, during which re-exposure to the allergen does not elicit an immediate response. Understanding this phenomenon could have significant implications for the management of urgent imaging needs in patients with known ICM hypersensitivity.

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