What is amiodarone-associated thyroid dysfunction?

Updated: Aug 28, 2020
  • Author: Mini Gopalan, MD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Amiodarone is a potent antiarrhythmic drug that is used to treat ventricular and supraventricular tachyarrhythmias. It is a benzofuran-derived, iodine-rich compound with some structural similarity to thyroxine (T4). Amiodarone contains approximately 37% iodine by weight. Each 200-mg tablet is estimated to contain about 75 mg of organic iodide, 8-17% of which is released as free iodide. Standard maintenance therapy with 200-mg amiodarone can provide more than 100 times the daily iodine requirement. It is highly lipid-soluble and is concentrated in the adipose tissue, muscle, liver, lung, and thyroid gland. [1]

The elimination half-life of amiodarone is highly variable, ranging from 50-100 days; total body iodine stores remain increased for up to 9 months after discontinuation of the drug. Thyroid abnormalities have been noted in up to 14-18% of patients receiving long-term amiodarone therapy. However, a meta-analysis suggested that with the lower doses of amiodarone (150-330 mg) incidence of thyroid dysfunction is 3.7%. The effects range from abnormal thyroid function test findings to overt thyroid dysfunction, which may be either amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH). [2, 3, 4, 5] Both can develop in apparently normal thyroid glands or in glands with preexisting abnormalities.

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