From the Guidelines
For a post-contrast rash, immediately stop the contrast administration if still ongoing and notify the radiologist or physician, then administer diphenhydramine (Benadryl) 25-50mg orally or IV for mild reactions. For mild reactions with just hives or itching, apply cool compresses to the affected areas and monitor the patient for at least 30 minutes. For moderate reactions with more extensive hives or mild facial swelling, consider adding H2 blockers like famotidine 20mg IV and oral corticosteroids such as prednisone 40-60mg 1. Severe reactions with breathing difficulty, significant swelling, or hypotension require immediate epinephrine (0.3-0.5mg of 1:1000 solution IM in the thigh), activation of emergency response, IV fluids, and possibly oxygen. Document the reaction in the patient's chart to prevent future exposure to the same contrast agent. These reactions occur because contrast media can trigger mast cell degranulation and histamine release, causing inflammatory responses. Patients with previous contrast reactions, asthma, or multiple allergies are at higher risk and may benefit from premedication before future contrast studies, although the evidence for premedication is conditional and of very low certainty 1. It is essential to distinguish between immediate index reactions associated with RCM and severe, delayed, cutaneous T-cell-mediated reactions, where premedication may add value to management 1. However, for patients with a prior history of allergic reactions to shellfish or seafood, anaphylactoid prophylaxis for contrast reaction is not beneficial 1. In patients with a history of prior anaphylactoid reaction, a regimen of prednisone and diphenhydramine may reduce the recurrence rate of anaphylactoid reactions 1. Given the diversity of clinical circumstances evaluated and low confidence in the literature base, higher certainty evidence is needed to better inform practice, and future recommendations could potentially change as a result of new information 1.
From the FDA Drug Label
Directions for itching of skin irritation, inflammation, and rashes: adults and children 2 years of age and older: apply to affected area not more than 3 to 4 times daily children under 2 years of age: ask a doctor for external anal and genital itching, adults: when practical, clean the affected area with mild soap and warm water and rinse thoroughly gently dry by patting or blotting with toilet tissue or a soft cloth before applying apply to affected area not more than 3 to 4 times daily children under 12 years of age: ask a doctor
For a post-contrast rash, apply hydrocortisone to the affected area not more than 3 to 4 times daily for adults and children 2 years of age and older.
- Clean the affected area with mild soap and warm water before applying, if practical.
- For children under 2 years of age or under 12 years of age, ask a doctor for guidance 2
From the Research
Post-Contrast Rash Management
- A post-contrast rash can be a sign of an allergic reaction to the contrast media used in imaging procedures 3.
- The severity of the rash can vary from mild to severe, and in some cases, it can be life-threatening 4, 5.
Treatment Options
- Topical steroids can be an effective treatment for a post-contrast rash, especially in cases where parenteral corticosteroids are not effective 3.
- Corticosteroid premedication has been shown to be helpful in reducing the overall rate of recurrence of acute allergic-like reactions to low osmolar contrast media in high-risk patients 4.
- Antihistamines, such as diphenhydramine, can also be used as part of a pretreatment regimen to prevent anaphylactoid reactions to radiographic contrast media 6, 7.
- In cases of severe allergic-like reactions, intramuscular epinephrine autoinjectors should be used promptly 5.
Prevention and Preparedness
- Patients with a history of previous anaphylactoid reactions to radiographic contrast media are at increased risk for subsequent reactions, and pretreatment regimens should be administered up to 13 hours before the anticipated procedure 6, 7.
- Emergency equipment should be available for all procedures involving contrast media, and radiologists should be trained in the management of contrast media reactions 5.