Iodine allergy: Common misperceptions.

PURPOSE: The current evidence regarding iodine-containing compounds and iodine allergy cross-reactivity is reviewed. SUMMARY: Iodine is an essential human nutrient found in the thyroid gland. It is used in the synthesis of the thyroid hormones thyroxine and triiodothyroxine. Patients who report having adverse reactions to iodine-containing substances are often labelled as having an "iodine allergy," which can result in delays in care or patients being denied essential iodinated contrast media (ICM) or other iodine-containing drugs. A literature review was conducted to evaluate the evidence regarding iodine allergy and iodine-containing drugs. Of 435 articles considered potentially appropriate for full review (plus 12 additional articles included on the basis of references from the eligible articles), 113 could not be obtained. After exclusion of 353 articles that did not meet all inclusion criteria, the remaining 81 articles were included in the review. The results of the literature review indicated that iodine has not been shown to be the allergen responsible for allergic reactions to iodinated contrast media, amiodarone, povidone-iodine, and other iodine-containing compounds. CONCLUSION: There is a lack of evidence to support cross-reactivity between iodine-containing compounds in so called iodine-allergic individuals.

Sulfonamide cross-reactivity: is there evidence to support broad cross-allergenicity?

PURPOSE: Published and manufacturer-provided data regarding potential cross-reactivity between antibacterial and nonantibacterial sulfonamide agents are reviewed. SUMMARY: An estimated 3-6% of the general population is allergic to sulfonamides and thus at risk for type I and other hypersensitivity reactions to sulfamethoxazole and other sulfonamide antibacterial agents. Concerns have been raised that a history of sulfa allergy may be associated with an increased risk of adverse reactions to a wide range of nonantibacterial sulfonamides, including certain antivirals, carbonic anhydrase inhibitors, cyclooxygenase-2- selective nonsteroidal antiinflammatory drugs, loop and thiazide diuretics, and sulfonylureas; concerns have also been raised that patients who have experienced an allergic reaction to one nonantibacterial sulfonamide may be at risk for an adverse reaction to others. Structurally, none of the nonantibiotic sulfonamides exhibit both of the features shown to be responsible for sulfonamide reactions (i.e., an N-containing ring attached to the N1 nitrogen of the sulfonamide group and an arylamine group at the N4 position), and only two agents (amprenavir and fosamprenavir) have the latter characteristic. A comprehensive literature search (1966-December 2011) identified nine case reports indicating possible cross-reactivity to sulfonamide medications; however, in most cases, adequate patient testing was not conducted to firmly establish either sulfa allergy or sulfonamide cross-sensitivity. The weight of evidence suggests that withholding nonantibacterial sulfonamides from patients with prior reactions to antibacterial sulfonamides or other nonantibacterial sulfonamides is not clinically justified. CONCLUSION: A review of the professional literature and manufacturer-provided data did not find convincing evidence of broad cross-reactivity between antibacterial and nonantibacterial sulfonamide agents.