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Specialty Practice Pharmacist, Ambulatory Care The Ohio State Medical Center 425 West 10th Avenue Columbus, Ohio 43210 fax 614/293-2867 melissa.snider{at}osumc.edu
Specialty Practice Pharmacist, Electrophysiology The Ohio State Medical Center
Faculty College of Pharmacy The Ohio State University
Published Online, July 22, 2008. www.theannals.com, DOI 10.1345/aph.1L158
Case Reports. A 64-year-old male with atrial fibrillation, hypertension, cardiomyopathy (ejection fraction 25%), tobacco use, history of transient ischemic attack, and syncope with a biventricular pacemaker/implantable cardioverter-defibrillator presented to the outpatient antiarrhythmic medications clinic for amiodarone monitoring one month after in-hospital initiation of therapy. Outpatient medications were twice-daily clonidine 0.2 mg and diphenhydramine 25 mg and once-daily amiodarone 200 mg, aspirin 162 mg, furosemide 20 mg, lisinopril 5 mg, lovastatin 20 mg, metoprolol extended-release 50 mg, triamterene/hydrochlorothiazide 37.5/25 mg, and warfarin 5 mg. "Iodine allergy—reaction: anaphylaxis" was noted on the patient's chart. He reported 2 previous reactions in the remote past to iodinated contrast dye, with the second reaction including facial swelling and trouble swallowing. There were no other known drug allergies. Since his hospital discharge, he had been taking oral diphenhydramine 25 mg twice daily for seasonal allergies. At follow-up 6 months later, the diphenhydramine dose had been reduced to 25 mg once weekly. Throughout follow-up, the patient tolerated amiodarone without any adverse reactions.
Two additional patients with atrial fibrillation, documented reactions to intravenous contrast dye in the remote past, and no other known allergies subsequently presented to the clinic. One patient had received iodinated contrast dye with an associated loss of consciousness and was told that it was a severe, near-fatal hypersensitivity reaction. The other patient who had received an intravenous contrast dye had experienced severe throat swelling that responded to diphenhydramine treatment. Both patients are currently tolerating amiodarone 100–200 mg daily with no symptoms of hypersensitivity.
Discussion. Amiodarone is contraindicated in patients with a known hypersensitivity to iodine.2 There is one report of 3 patients who had reactions to iodine-containing compounds and who received amiodarone without anaphylactic or anaphylactoid reactions.3 In contrast, there is a report of a patient with iodinated radiocontrast-induced urticaria and subsequent anaphylaxis after one dose of oral amiodarone.4
Several factors may influence the reasons that "iodine-allergic" patients may fail to cross-react to amiodarone.3 The bioavailability and absorption of oral amiodarone, and therefore of iodine, can vary significantly among individuals. Additionally, contrast-mediated reactions may result from factors (eg, ionic content or hypertonicity) other than iodine content, given that both iodinated and noniodinated contrast dye can induce histamine release. Past reactions do not always predict future reactions, as these are not immunoglobulin E antibody mediated. The potential for anaphylactic or hypersensitivity reactions is less in newer dyes than in older, ionic, highly osmolar contrast dyes.
In our first patient, we assessed the potential role of diphenhydramine cotreatment in masking a hypersensitivity reaction. This was ruled out based on the relatively low dose and the lack of symptoms after decreasing the diphenhydramine dose to 25 mg per week. Thus, the previous reaction to the contrast medium that this patient experienced was unlikely due to the iodine content, since he did not have a subsequent reaction to amiodarone.
There is a need to investigate patients' claims of past reactions to iodinated radiocontrast agents carefully to determine the likely risk that these represent true hypersensitivity reactions to iodine. In patients with reactions to iodinated intravenous contrast, an iodine allergy is not consistently present, although the chart may be marked as such. Clearly, caution should be exercised in patients with an "iodine allergy," as known hypersensitivity to iodine is a contraindication to amiodarone therapy.2 The true potential for cross-reactions with amiodarone should be determined, and risk versus benefit of amiodarone therapy must be individually assessed.
Footnotes
Letters are subject to review prior to acceptance. They should address areas related to pharmacy practice, research, or education, or articles recently published. Corrections of previously published material also are accepted. Letters are limited to no more than five authors. In cases where adverse effects or drug interactions are described, the Naranjo ADR probability scale (Clin Pharmacol Ther 1981;30:239-45) or DIPS scale (Ann Pharmacother 2007;41:674-80. DOI 10.1345/aph.1H423), respectively, should be used to determine the likelihood that the adverse effect or interaction was drug-related. Text: limit 500 words. References: limit 5. Art: limit 1 table or figure.
References
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