What is the recommended pre-treatment regimen with Benadryl (diphenhydramine) and steroids (e.g. prednisone) for patients at high risk of allergic reactions to contrast agents?

Contrast Media Pretreatment Protocol for High-Risk Patients

For patients with a history of prior anaphylactoid reaction to contrast media, the recommended pretreatment regimen is 50 mg of prednisone given orally at 13 hours, 7 hours, and 1 hour before contrast administration, plus 50 mg of diphenhydramine orally or intramuscularly 1 hour before contrast administration. 1, 2

Patient Risk Assessment

High-risk patients who should receive premedication include:

• Patients with previous moderate to severe contrast reaction (highest risk, 16-44% recurrence risk without premedication) 1, 2
• Asthmatic and atopic patients 1
• Patients on beta-blockers 1
• Patients with cardiovascular disease 1

Important: Contrary to common belief, seafood/shellfish allergy and "iodine allergy" are NOT risk factors for contrast reactions and do not warrant premedication based solely on these histories 2

Standard Premedication Protocol (Non-Emergency)

For elective procedures with adequate preparation time:

1. Prednisone 50 mg orally at:
   • 13 hours before contrast administration
   • 7 hours before contrast administration
   • 1 hour before contrast administration
2. Diphenhydramine 50 mg orally or intramuscularly 1 hour before contrast administration 1, 2

Alternative Premedication Protocols

If the standard protocol cannot be followed:

• Alternative oral regimen:

  • Prednisone 60 mg orally the night before and morning of procedure
  • Diphenhydramine 50 mg orally or intramuscularly 1 hour before contrast 2

• Lower-dose steroid option:

  • Cetirizine 10 mg with prednisone 20 mg (instead of 50 mg) at 13,7, and 1 hour before contrast 3
  • Note: Research shows similar efficacy between 20 mg and 50 mg prednisone doses 3

Emergency Premedication Protocol

For urgent procedures when standard premedication timing is not possible:

• Hydrocortisone 200 mg IV immediately and every 4 hours until contrast administration
• Diphenhydramine 50 mg IV/IM 1 hour before contrast administration 1, 2, 4

Additional Considerations

1. Contrast Material Substitution:

   • Using a different contrast agent than the one that previously caused a reaction may be more effective than steroid premedication with the same agent 5
   • Consider using low-osmolar or iso-osmolar contrast agents instead of high-osmolar agents 2

2. Special Precautions:

   • Patients on beta-blockers may require more intensive treatment if reactions occur 1, 2
   • Minimize contrast volume in all patients, especially those with chronic kidney disease 2
   • Have emergency medications and equipment readily available regardless of premedication 2

3. Breakthrough Reactions:

   • Despite premedication, approximately 3.4% of high-risk patients may still experience moderate to severe reactions 2, 6
   • Most repeat reactions (93%) are of similar or lesser severity than the index reaction 5

When to Consider Alternative Imaging

• For patients with history of severe reactions despite premedication
• When clinically appropriate, non-contrast imaging methods should be considered 2, 6

By following these protocols, the risk of recurrent contrast reactions can be significantly reduced, though not completely eliminated. Always be prepared to treat breakthrough reactions promptly.