“Patients on amiodarone can develop either hyperthyroidism or hypothyroidism. It is recommended that a patient on amiodarone have baseline thyroid function tests (free T4, TSH) with follow-up testing every 6 months to monitor for these conditions.” ABFM
Other sources recommend checking TSH prior to treatment with amiodarone, then at 4-month intervals while on amiodarone, and for one year after amiodarone is discontinued.
Amiodarone has a high iodine content. “Amiodarone’s high iodine content causes inhibition of 5′-deiodinase activity. Most patients remain euthyroid. Amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH) may occur depending on the patient’s iodine status and prior thyroid disease. AIT is caused by excess iodine-induced thyroid hormone synthesis (type I AIT) or by destructive thyroiditis (type II AIT). If the medical condition allows it, d/c amiodarone in type I AIT. Otherwise, large doses of thioamides are required. Type II AIT is treated with corticosteroids. Mixed cases require a combination of both drugs. Potassium perchlorate has been used to treat resistant cases of type I AIT but use is limited by toxicity. Thyroidectomy, plasmapheresis, lithium, and radioiodine are used in select cases of AIT. AIH is successfully treated with levothyroxine. Screening for thyroid disease before starting amiodarone and periodic monitoring of thyroid function tests are advocated.” Hema Padmanabhan, MD, FACP
References:
http://www.medscape.com/viewarticle/728286
Amiodarone: Guidelines for use and monitoring. Am Fam Physician 2003;68(11):2189-2196. 2) Vassallo
Prescribing amiodarone: An evidence-based review of clinical indications. JAMA 2007;298(11):1312-1322.
A practical guide for clinicians who treat patients with amiodarone: 2007. Heart Rhythm 2007;4(9):1250-1259.
Amiodarone and thyroid dysfunction. South Med J 2010;103(9):922-930.