Since non-ionic contrast has been widely utilized, the incidence of allergic reactions has decreased. However, some patients may still be allergic to IV contrast agents.
Since we are unable to determine with any certainty which patients may have a reaction, it is only after a prior reaction that patients are usually pre-medicated. Some patients may have experienced a severe reaction to IV contrast, these patients may not be good candidates for premedication, but the importance of the scan needs to be weighed against the risk to the patient. In some instances clinicians and/or radiologists may decide to pre-medicate patients with a history of multiple allergies to other things as a precautionary measure.
There are variations of pre-medications that are acceptable. However, if a pre-medication protocol is given, it usually involves giving corticosteroids and/or antihistamines. The dosage and time frames vary. These regimens have shown to be very helpful in reducing the risk of a recurrent reaction to the contrast. It is our protocol to give the patients 40 mg (PO) m of prednisone 24, 12 and 2 hours prior to the CT scan. For example, if a patient is to have a CT scan at 10 am on Monday. The 1st dose should be given at 10 am on Sunday, the 2nd dose at 10pm on Sunday and the final dose at 8 am on Monday.
Of course members of the CT department need to be trained and able to handle an emergency situation in the event a patient does have an allergic reaction.
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