Amiodarone and hyperthyroidism

The Swiss information for healthcare professionals for amiodarone cites hyperthyroidism as a common ADR that can occur during treatment or several months after it has ended.

Key words: Hyperthyroidism; amiodarone; thyroiditis; iodine level
Incident data	Description
Year: 2022 Age: 85 Sex: Female Medicinal product: Amiodarone Indication: Paroxysmal atrial fibrillation ADR: Hyperthyroidism	The patient’s TSH was within normal range before she started amiodarone. Eight months after treatment started, TSH had decreased (< 0.01 mU/L), while T4 was very high and T3 within normal values. Thyroid antibodies were unremarkable. No clinical symptoms such as restlessness, tremors, fast pulse, sweating or exercise intolerance were reported. In the opinion of the doctors treating the patient, the hyperthyroidism was a consequence of her amiodarone treatment. This was discontinued and thyrostatic treatment with carbimazole was started. Nothing is known about her subsequent progress. A causal connection was deemed to be probable.
Year: 2022 Age: 46 Sex: Male Concomitant diseases: cardiomyopathy and type 2 diabetes among others Medicinal product: Amiodarone Indication: Symptomatic atrial fibrillation ADR: Hyperthyroidism	The patient had taken several short courses of amiodarone for symptomatic atrial fibrillation; however this had stopped following elective electrical cardioversion. Elevated TSH of 6.08 mU/L [ref.: 0.5-4.5 mU/L] with normal T3 and T4 was measured at this time. The patient was admitted to hospital with decompensated heart failure three months after discontinuing amiodarone. TSH was now suppressed to 0.02 mU/L and free T3 (12.2 pmol/L) and T4 (63.0 pmol/L) were increased. A thyroid ultrasound scan revealed normal volume and no nodules. Manifest hyperthyroidism was diagnosed and interpreted as amiodarone-induced type 2 (toxic) hyperthyroidism. The only clinical symptoms were irritability and intermittent sweating. The patient was treated with 60 mg prednisolone taken orally once daily. He subsequently presented once again in the emergency department in a reduced general condition with weight-bearing-related chest pain radiating into the epigastrium and lower abdomen. The patient’s thyroid values deteriorated despite prednisolone treatment, ultimately necessitating an emergency total thyroidectomy. A causal connection was deemed to be probable.

Summary and recommendation

Amiodarone contains iodine and can therefore lead to excessive iodine intake. Since it is a lipophilic medicine and has a half-life of 20 to 100 days, iodine levels remain elevated for several months after it has been discontinued.

A clinical distinction is made between amiodarone-induced hyperthyroidism of type I (increased thyroid hormone production caused by elevated iodine levels) and type II (direct toxic effects of amiodarone on the thyroid with destructive thyroiditis and elevated release of thyroid hormones).

Severe forms with an occasionally fatal progression represent a therapeutic emergency. Treatment must be adapted to each individual case.