A patient with a history of seafood allergy and previous mild reaction to iodinated contrast is scheduled for an emergency CT with contrast. What is the most appropriate premedication regimen to reduce risk of repeat reaction?

• A Intravenous adrenaline 0.5 mg 10 minutes before contrast injection
• B Oral prednisolone 50 mg at 13, 7, and 1 hour before the procedure plus diphenhydramine 50 mg 1 hour before ✓
• C Oral ranitidine 150 mg 1 hour before procedure only
• D Intravenous hydrocortisone 100 mg immediately before contrast injection

Explanation

The standard ACR-recommended premedication protocol for patients with prior mild-moderate iodinated contrast reaction is: methylprednisolone 32 mg (or prednisolone 50 mg) orally at 13 hours, 7 hours, and 1 hour before contrast, plus diphenhydramine 50 mg IV/IM/PO 1 hour before. Corticosteroids given less than 4–6 hours before are ineffective; a single IV dose immediately before provides no proven benefit. Seafood allergy is a common misattributed risk factor but does not directly contraindicate contrast (the risk is similar to general population). Adrenaline is the treatment for anaphylaxis, not prophylaxis.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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