D1.86 - Hypersensitivity Reaction to Lugol’s Solution: A Case Report

Background: Iodine antiseptic allergy is rare, presenting as contact dermatitis, urticaria, or anaphylaxis. Diagnosis relies on clinical history and non-standardised skin tests with the culprit agent and its compounds. 

Case Presentation: A 47-year-old female with no prior drug hypersensitivity experienced a severe adverse event during a colposcopy. Approximately 15 minutes after the topical application of Lugol’s solution (5% iodine, 10% potassium iodide), she developed genital pruritus and discomfort, rapid-onset localised oedema, hypotension, and loss of consciousness. Supportive care was provided, and she recovered fully. An allergological evaluation was performed. Skin prick tests (SPTs) with elemental iodine (1:1), potassium iodide (1:1), Lugol’s solution (1:10 and 1:1), iodopovidone (1:10 and 1:1), and povidone (1:1) were negative. However, intradermal tests (IDTs) with Lugol’s solution at 1:1000 and 1:100 dilutions were positive, as were IDTs with iodopovidone (10% iodine) at the same dilutions. IDTs with elemental iodine (1:1000), potassium iodide (1:1000), and povidone (1:1000) were negative, confirming hypersensitivity to iodine-based antiseptics. 

Discussion: The pathogenesis of these reactions appears related not to iodine itself, but to its chemical formulation. Lugol’s solution and povidone-iodine release significant amounts of free iodine, which may act as a hapten triggering an IgE-mediated response. This mechanism is supported by previous reports of anaphylactic-like reactions to Lugol’s solution. Additionally, hypersensitivity to povidone, a component of iodopovidone, suggests that the allergenic stimulus may reside in the compound formulation rather than in elemental iodine. These findings contribute to the growing evidence that hypersensitivity to iodine-based antiseptics is multifactorial, involving both iodine's intrinsic properties and its carrier matrix, particularly the bioavailability of free iodine. Misinterpretation of iodine allergy can lead to unnecessary avoidance of essential agents (e.g. iodinated contrast media). Comprehensive, component-specific allergological testing is crucial for risk stratification and patient management. 

Conclusions: This case underscores that iodine hypersensitivity is primarily due to specific antiseptic formulations rather than iodine itself. Improved understanding of these mechanisms is essential to guide clinical decisions and ensure patient safety in procedures involving iodine-based compounds.