From the Guidelines
For patients at risk of allergic reactions prior to an MRI with contrast agent, the recommended prednisone premedication regimen is 50 mg of oral prednisone given at 13 hours, 7 hours, and 1 hour before the contrast administration, for a total of three doses, as supported by 1. This should be combined with 50 mg of oral diphenhydramine (Benadryl) 1 hour before the procedure. The following key points are essential to consider:
- The incidence of anaphylactoid reactions to contrast media is low, but recurrence rates without prophylaxis can be significant, ranging from 16% to 44% in patients with a history of prior anaphylactoid reactions, as noted in 1.
- Pretreatment with corticosteroids and antihistamines has been shown to reduce the risk of recurrent anaphylactoid reactions, with a regimen of 50 mg of prednisone administered 13 hours, 7 hours, and 1 hour before the procedure, along with 50 mg of diphenhydramine 1 hour before the procedure, being effective, as mentioned in 1.
- For emergency situations where the full 13-hour protocol cannot be followed, an alternative regimen consists of 40 mg of oral prednisone or 200 mg of intravenous hydrocortisone given immediately and repeated every 4 hours until the procedure, along with 50 mg of diphenhydramine 1 hour before contrast administration, as discussed in 1.
- It is crucial to inform patients that even with premedication, a small risk of breakthrough reactions remains, and they should promptly report any symptoms like itching, hives, or difficulty breathing during or after the procedure, as emphasized in 1. Some important considerations include:
- The use of lower-osmolality contrast agents may reduce the risk of anaphylactoid reactions, as suggested in 1.
- Patients with a history of prior anaphylactoid reactions to contrast media are at increased risk, and pretreatment is particularly important in this group, as highlighted in 1.
- The role of glucocorticoids and antihistamines in preventing biphasic anaphylaxis is uncertain, and more research is needed to determine their effectiveness, as noted in 1.
From the Research
Recommended Prednisone Regimen
- The recommended prednisone regimen for patients at risk of allergic reactions prior to an MRI with contrast agent is not explicitly stated for MRI contrast agents, but studies on iodinated contrast media provide some guidance 2, 3, 4.
- A study on iodinated contrast media suggests that premedication with cetirizine and prednisone (20 mg or 50 mg) 13,7, and 1 hour before the procedure can be effective in preventing adverse reactions 2.
- Another study found that a two-dose corticosteroid regimen (32 mg of methylprednisolone 6-24 hours and 2 hours before injection of contrast material) can confer protection against adverse reactions to nonionic contrast media 3.
- A study from 1984 found that pretreatment with prednisone (50 mg) 13,7, and 1 hour before the procedure, along with diphenhydramine (50 mg) 1 hour before the procedure, can decrease the reaction rate to 9.0% 4.
Considerations for MRI Contrast Agents
- While the studies mentioned above focus on iodinated contrast media, a review of adverse reactions to gadolinium contrast media (used in MRI) found that severe anaphylactoid reactions can occur, although rarely 5.
- Updated guidelines from the ESUR Contrast Media Safety Committee suggest that selecting an alternative contrast medium based on the results of an allergy evaluation is a safer and more effective approach than premedication for preventing recurrent hypersensitivity reactions 6.
Key Points
- Premedication with corticosteroids, such as prednisone, may be considered for patients at risk of allergic reactions to contrast agents, but the optimal regimen is not well established for MRI contrast agents 2, 3, 4.
- A thorough allergy evaluation and selection of an alternative contrast medium may be a more effective approach than premedication for preventing recurrent hypersensitivity reactions 6.