Contrast Reactions and Pre-Medication

Prophylaxis Policy for Patients Allergic to IV Contrast

What patients require premedication prior to IV contrast?

A prior allergic-like or unknown type reaction to the same class of contrast medium is considered the greatest risk factor for predicting future adverse events. Premedication prior to administration of intravenous contrast is recommended in this group of patients.

In general, patients with unrelated allergies are at a 2- to 3-fold increased risk of an allergic-like contrast reaction, but due to the modest increased risk, restricting contrast medium use or premedicating solely on the basis of unrelated allergies is not recommended. Patients with shellfish or povidone-iodine (e.g., Betadine®) allergies are at no greater risk from iodinated contrast medium than are patients with other allergies (i.e., neither is a significant risk factor).

In patients with reported prior contrast allergy or reaction:

1. Ascertain the specific details of the prior reaction.  Determine:
   1. If the patient had a true reaction to intravascular contrast material
   2. Type of contrast used (if available)
   3. Type of reaction and severity
   4. Treatment and its result
   5. Level of patient anxiety
2. In addition to intravascular contrast administration, the following scenarios should be considered in patients with contrast allergy:
   1. Administration of oral contrast.  1-2% of oral contrast could be absorbed.  So for someone who has a severe contrast allergy, they should get dilute barium as an oral contrast agent.  If prior mild reaction and minimum risk of perforation/leak, no need to premedicate.  For moderate reactions or risk of peritoneal leak, consider premedication or dilute barium alternate oral contrast.
   2. Arthrograms.  Because allergic-like reactions are dose-independent, and arthrograms use a needle and cross the bloodstream, use the same premedication strategy for arthrograms that is used for intravenous media. For patients with known contrast allergies, appropriate to premedicate or switch to US if possible.
   3. Hysterosalpingograms: In patients with patent fallopian tubes, there is peritoneal spill of contrast.  Intraperitoneal contrast is absorbed (intraperitoneal=intravascular).  Because of the dose independence, premedication for HSGs should be performed in patients with known contrast allergies.
3. Determine if an examination without contrast can provide adequate diagnostic information.
4. If still convinced of the need for intravascular contrast, the service requesting  the scan should:
   1. Contact the radiologist scheduled on service for the proposed date of the study (GI/GU, CT, Angiography, Neuroradiology, or on-call resident for overnight/weekend Emergency Department patients).  If the staffing schedule is not available for the proposed date of the examination, then the Chief of the GI/GU Service (Dr. Perry Pickhardt), CT Service (Dr. Meghan Lubner), Angiography/Interventional Service (Dr. Orhan Ozkan), or Neuroradiology Service (consultant for the day) should be contracted.
   2. Discuss why an alternative imaging method will not suffice
   3. If the risk is determined to be acceptable; schedule the contrast examination and transmit prophylaxis instructions.
5. Routine Contrast Reaction Prophylaxis (12 hour):
   1. Methylprednisolone (Medrol)
      1.  32 mg by mouth at 12 and 2 hours before contrast injection.
   2. Diphenhydramine (Benadryl):
      1. 50 mg intramuscular or oral 1 hour before contrast injection OR
      2. 50 mg (or 25 mg per height/weight indication) intravenously 15-20 min before contrast injection
         Note:  The Benadryl must be used with the proviso that the patient does not drive a car or operate heavy machinery 4-6 hours after the Benadryl is administered.
         NEJM 1987; 317: 845-849.
   3. If a patient is unable to take oral medication, consider the 5 hr regimen detailed in #6.  Alternatively the methylprednisolone may be substituted with 200 mg hydrocortisone IV at 13, 7, and 1 hour before contrast administration. If a patient is allergic to diphenhydramine in a situation where diphenhydramine would otherwise be considered, an alternate anti-histamine without cross-reactivity may be considered, or the anti-histamine portion of the regimen may be dropped.
6. Rapid Contrast Reaction Prophylaxis (5 hours):
   1. To be used only in a truly urgent situation after discussion between the requesting service and the appropriate radiology service.
   2. The requesting service must place a note in HealthLink outlining the necessity of contrast-enhanced examination and the rapid prohpylaxis protocol.
   3. Hydrocortisone:
      1. 200 mg intravenously 5 and 1 hour before contrast injection
   4. Diphenhydramine (Benadryl):
      1. 50 mg intravenously 1 hour before contrast injection
7. In addition to steroid premedication, changing the culprit iodinated agent if known may decrease the risk of repeat allergic reaction. Consider substitution of an iso-osmolar agent (iodixanol) if a low osmolar agent was previously administered.

Greenberger PA et al. Emergency administration of radiocontrast media in high-risk patients. J Allergy CLin Immunol. 1986; 77(4): 630-634.

Resources

• Mervak BM, Cohan RH, Ellis JH, Khalatbari S, Davenport MS.  Premedication administered 5 hours before CT compared with a Traditional 13-hour Oral regimen. Radiology 2017; 285(2), 425-433.
• McDonald JS, Larson NB, Kolbe AB et al. Prevention of Allergic-like Reactions at Repeat CT: Steroid Pretreatment versus Contrast Material Substitution. Radiology 2021; 000:1-8.

Updated July 2020

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Contrast Reactions and Pre-Medication