Contrast Reaction Prophylaxis

The primary indication for premedication is pretreatment of "at risk" patients who require contrast media. Such regimens have been shown in clinical trials to decrease the frequency of anaphylactoid contrast reactions. However, no regimen has elimanate repeat reactions completely. Pretesting is not predictive, may itself be dangerous, and is not recommended.

Several premedication regimens have been proposed to reduce the frequency and/or severity of reactions to contrast media. Frequently used regimens are:

Protocol A: Oral Corticosteroid/antihistamine (preferred) Prednisone 50 mg by mouth at 13 hours, 7 hours, and 1 hour before contrast injection, plus Diphenhydramine (Benadryl) 50 mg by mouth 1 hour before contrast injection.

Protocol B: Oral Corticosteroid alone Methylprednisolone (Medrol) 32 mg by mouth at 12 hours and 2 hours before contrast injection.

Protocol C: Intravenous Corticosteroid/antihistamine Hydrocortisone 200mg IV at 13 hours, 7 hours, and 1 hour before contrast injection, plus Diphenhydramine (Benadryl) 50 mg IV 1 hour before contrast injection.

Use protocol A unless otherwise contraindicated. Oral administration of steroids seems preferable to intravenous administration. If the patient is unable to take oral medication, IV hydrocortisone may be substituted for oral prednisone (Protocol C). Patients already on corticosteroids and pediatric patients may require modifications to the protocol. Outpatients taking an antihistamine should should not drive after the examination.

For patients at an increased risk of adverse reaction to contrast, studies show that nonionic contrast has a lower reaction rate than ionic contrast plus premedication. The combination of premedication with nonionic contrast has shown a further reduction in reaction rates. However, no controlled studies are available to determine whether pretreatment alters the incidence of serious reactions.

Reference: ACR manual on Contrast Media, 4th edition.
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