As a cardiovascular pharmacist, you will be asked more about the possible effects of amiodarone (Cordarone) on thyroid functioning. We know, amiodarone is an iodine source (39% iodine by weight), and the patient's response to iodine is determined by pre-existing state of thyroid. Amiodarone may cause hypo- or hyperthyroidism...
There are 2 types of HYPERthyroid effect/thyrotoxicosis of amiodarone. In TYPE 1 (Jod–Basedow effect), amiodarone load induces thyroid synthesis in abnormal thyroid (e.g., Graves' or goiter) or in iodine-deficient patient which cause HYPERthyroid state. In TYPE 2 (Drug-induced lysosomal destructive thyroiditis), release of preformed hormone in patients without intrinsic thyroid abnormalities.
- Doppler can reveal high vascularity in Type 1, low vascularity in Type 2 (but this is limited by operator-dependency and has low sensitivity).
- Iodine uptake scans are variable in Type 1 but low in Type 2.
- In practice, can be hard to distinguish Types 1 and 2.
HYPOthyroidism (Wolff–Chaikoff effect). Iodine load inhibits thyroid peroxidase AND decreased thyroid release and cause HYPOthyroid. It is more common in females or autoimmune thyroiditis.
How should amiodarone thyroiditis be managed? Patients with hypothyroidism will be treated with levothyroxine and continue amiodarone. For Type I, stop amiodarone if possible and administer thioamides (e.g., PTU). For Type 2, stop amiodarone if possible, steroids may have modest benefit. Given difficulty distinguishing between Type 1 and Type 2, often treat for both empirically. Thyroidectomy is an option in resistant cases. After discontinuation of amiodarone, its effect will will be still present. Amiodarone is stored in adipose tissue and can linger for > 6 months. GET OUR NOTE, "Pay attention when patients are on amiodarone".
REFERENCES
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Basaria S, Cooper DS. Amiodarone and the thyroid. Am J Med. 2005 Jul;118(7):706-14. Available at: https://pubmed.ncbi.nlm.nih.gov/15989900
Jameson J, Weetman AP. Chapter 341: Disorders of the thyroid gland. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J, eds. Harrison's Principles of Internal Medicine. 18th ed. New York, NY: McGraw-Hill; 2012