Neuroradiology Division

Contrast Allergy

Patients who have an allergy to radiographic contrast material (CT contrast) need pre-medication if an alternative study cannot be done. Often MRI can replace a CT scan with contrast and in that case MR is preferred.

Pre-medication for prior allergic reaction to contrast material includes:

• 50 mg Prednisone P.O. 25 hours before the study
• 50 mg Prednisone P.O. 13 hours prior to the study
• 50 mg Prednisone P.O. 1 hour prior to the study
• 50 mg Benadryl I.V. 2 hours before the study

For emergent patient who is allergic to radiographic contrast material (CT contrast) and needs an emergent study and regular pre-medication doesn’t work, the following regiment can be used.

• 100 mg of Solumedril I.V.
• 50 mg Benadryl I.V.

There is no cause reaction between the contrast material used for CT and the contrast material used for MR imaging. An alternative method is to use the MR contrast material for a CT scan. It will show up on CT although slightly less dense than regular CT contrast material.

We are often asked about shellfish allergy and there is no association between allergy to radiographic contrast material (CT or MRI) and shellfish allergies. Therefore, there is no need for pre-medication on the patient who is allergic to shellfish but has no documented case of contrast material allergy.