What is the premedication for iodine (contrast media) allergy?

From the Guidelines

For patients with a history of iodine allergy who need to undergo procedures requiring iodinated contrast media, premedication is not recommended based solely on a history of seafood or shellfish allergy, as the risk of anaphylactoid reaction is low and the pathophysiology of adverse effects of iodinated contrast media is poorly understood 1. The concept of an "iodine allergy" is often misunderstood, and reactions attributed to iodine are actually reactions to the contrast media itself rather than the iodine component 1. According to the most recent and highest quality study, there is no evidence to suggest that patients with seafood or shellfish allergies are at risk for an anaphylactoid reaction from exposure to contrast media, and iodine does not mediate seafood, shellfish, or contrast media reactions 1. Some key points to consider include:

• The incidence of anaphylactoid reactions to contrast media is low, around 1%, and the incidence of severe reactions may be as low as 0.04% 1.
• Pretreatment of patients with prior anaphylactoid reactions reduces the recurrence rate to close to zero, but this is not recommended for patients with a history of seafood or shellfish allergy alone 1.
• The American College of Radiology guidelines clarify that neither shellfish allergy nor an allergic reaction to topical povidone-iodine is considered as a risk factor for iodine allergy 1.
• The term “iodine allergy” should not be used in the context of RCM reactions, as ADRs associated with RCM do not relate to iodine 1. In practice, a thorough medical history and assessment of the patient's individual risk factors should guide the decision to use premedication, rather than relying solely on a history of seafood or shellfish allergy 1.

From the Research

Pre-medication for Iodine Allergy

• There is no evidence to support the existence of an "iodine allergy" as iodine is not the allergenic determinant in reactions to iodinated drugs or foods rich in iodine 2, 3.
• Patients who claim to have an iodine allergy may have had previous reactions to shellfish consumption or to imaging procedures that used iodine-based contrast agents, but these reactions are not due to iodine itself 4, 3.
• For patients who have had a previous reaction to radiographic contrast media, pretreatment with prednisone plus diphenhydramine or prednisone and diphenhydramine plus ephedrine can decrease the reaction rate 5.
• Topical steroids may be effective in treating allergic reactions to iodine contrast, especially in cases where parenteral steroids are not effective 6.
• Skin patch testing can be performed prior to surgery to determine if a patient has a true allergy to povidone-iodine, which is rare 4.

Treatment Options

• Pretreatment with prednisone and diphenhydramine, with or without ephedrine, can be effective in reducing the risk of anaphylactoid reactions to radiographic contrast media 5.
• Topical steroids may be used to treat allergic reactions to iodine contrast, especially in cases where parenteral steroids are not effective 6.
• Dilute povidone-iodine (0.1-0.25%) can be used to kill microbes quickly and effectively, with little risk of epithelial toxicity 4.

Diagnostic Approach

• Allergic hypersensitivity to iodinated contrast agents does not contraindicate the use of other iodinated drugs 2.
• An allergological assessment is required to confirm the immune mechanism, identify the culprit drug or substance, and identify cross-reactivity, especially with iodinated contrast media 3.
• Immediate-reading skin tests and delayed-reading skin testing can be used to assess immediate and non-immediate allergic hypersensitivity, respectively 2, 3.