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Pre-Medication Policy

For Planned Administration of Contrast Agents:
Previous reaction to allergens (eg shellfish, peanuts, medications, etc):
Mild Moderate Severe
None None None
Previous reaction to same class of contrast agent going to be given:
Mild Moderate Severe
None Pre-medicate and use different agent Do not give contrast*
Previous reaction to a different class of Contrast agent than type to be given:
Mild Moderate Severe
None None None

*Unless in the opinion of the responsible health care professional and supervising radiologist, the potential benefits outweigh the risks i.e. emergency situations. In these instances, clinical provider should accompany the patient to radiology suite (whenever feasible) to aid in management if a repeat reaction occurs.

Premedication with steroids and Benadryl is recommended only for patients who have had a reaction to contrast of a similar class (iodinated agents used during CT are one class, gadolinium based agents used during MRI are separate class) to the one planned to be given. Prophylaxis for those with reactions to other allergens is not necessary.

This guideline has been drawn up based on the following information:

  • Current estimated overall reaction risk in the general population of children and adults is less than 1% (in range of 0.2-0.6%) (Wang et al., Dillman et al.)
  • Patients with a prior reaction to the same class of contrast agent being administered are known to be at highest risk for repeat reaction, 3 – 11% overall reaction rate with 2% break-through reaction rate even with pre-medication during CT (Mervak et al. Lasser et al).
  • The current standard of care in the United States is to pre-medicate patients with steroids and diphenhydramine to decrease risk of repeat contrast reaction in patients who have had a reaction in the past to a similar class contrast agent if it was moderate or severe (see table below).
  • An IV steroid regimen (Recommended regimen below) is likely non-inferior compared to a longer PO regimen and is therefore recommended in the ED and in-patient setting to expedite imaging when needed (Mervak et al).
  • In certain clinical circumstances the urgency of a contrast enhanced CT or MRI may outweigh the benefits and time needed to complete approved premedication protocol, necessitating that contrast medium be given in absence of premedication or with a variation in the pre-treatment protocol. This determination should be jointly agreed upon by supervising radiologist and ordering clinician and potentially the patient (if feasible) with documentation in medical record.
Allergic Like Reaction Definitions¹:

Limited urticaria² / pruritis²Diffuse urticaria / pruritis
Diffuse edema, or facial edema with dyspnea
Nasal congestion
Diffuse erythema, stable vital signs
Diffuse erythema with hypotension
Cutaneous Edema
Facial edema without dyspneaLaryngeal edema with stridor and/or hypoxia
Sneezing / conjunctivitis / rhinorrhea
Throat tightness or hoarseness without dyspnea Wheezing / bronchospasm, significant hypoxia
Limited “itchy”/“scratchy” throat
Wheezing / bronchospasm, mild or no hypoxia
Anaphylactic shock (hypotension + tachycardia)

¹ Physiologic reactions like nausea, vomiting, feeling of warmth are unlikely to benefit from pre-medication
² If the urticaria/pruritis required medical treatment it should be considered moderate severity.


  • Wang CL, Cohan RH, Ellis JH, Caoili EM, Wang G, Francis IR. Frequency, outcome, and appropriateness of treatment of nonionic contrast media reactions. AJR 2008; 191:409–415.
  • Lasser EC, Berry CC, Mishkin MM, Williamson B, Zheutlin N, Silverman JM. Pretreatment with corticosteroids to prevent adverse reactions to nonionic contrast media. AJR 1994; 162:523–526.
  • Mervak BM, Davenport MS, Ellis JH, et al. Breakthrough reaction rates in high-risk inpatients premedicated before contrast-enhanced CT. AJR 2015; 205:77-84.
  • Dillman JR, Strouse PJ, Ellis JH, Cohan RH, Jan SC. Incidence and severity of acute allergic-like reactions to i.v. nonionic iodinated contrast material in children. AJR 2007; 188:1643-1647.
  • Mervak BM, Cohan RH, Ellis JH, Khalatbari S, Davenport MS. Intravenous Corticosteroid Premedication Administered 5 Hours before CT Compared with a Traditional 13-Hour Oral Regimen. Radiology 2017; 285:425-433.
  • American College of Radiology Contrast Manual. 2020.

Pre-Medication Regimen

Adult Out-patients:

  • 50mg prednisone PO 13, 7 and 1 hour before the injection.
  • 50mg diphenhydramine (Benadryl®) IV/PO within 1 hour of the injection.

Adult ED and In-Patients:

  • 200mg hydrocortisone IV 4 hours before injection.
  • 50mg diphenhydramine (Benadryl®) IV/PO within 1 hour of the injection.

Pediatric Out-patients (For patients less than 50kg):

  • Prednisone 0.7mg/kg (not to exceed 50mg) PO 13, 7 and 1 hour before the injection OR Prednisolone 0.7mg/kg (not to exceed 50mg) PO 13, 7 and 1 hour before the injection.
  • Diphenhydramine (Benadryl®) 1mg/kg IV/PO (not to exceed 50mg) within 1 hour of the injection.

Pediatric ED and In-Patients:

  • Hydrocortisone 1mg/kg (not to exceed 200mg) IV 4 hours before injection.
  • Diphenhydramine (Benadryl®) 1mg/kg IV/PO (not to exceed 50mg) within 1 hour.

Premedication order set is linked to EPIC order entry if contrast study ordered in patient with relevant contrast allergy documented in EPIC Allergies

Order set can also be found manually by searching using word "Contrast" in EPIC

What do I do if patient is allergic to a drug in the premedication order set?

Alternate premedication can be used if the patient is known to tolerate other classes of steroids. If needed, allergy consult may be needed for proper skin prick testing to find a suitable alternate (in many cases, the patient is not allergic to the drug itself but an additive in the drug).

For allergies to Benadryl, alternate antihistamine can be used that patient is known to tolerate.

Possible PO alternate steroid regime is 32 mg methylprednisolone 12h and 2h prior to IV contrast administration

Possible PO alternate antihistamine is Claritin or Zyrtec 10mg PO 1h prior to IV contrast administration.