AMIODARONE AND THYROID-DYSFUNCTION

Amiodarone is a potent and widely used antiarrhythmic drug that bears a structural resemblance to thyroid hormones. The high iodine content of the drug determines that amiodarone induces changes in circulating concentrations of thyroid hormones, largely through inhibition of conv ersion of thyroxine (T4) to tri-iodothyronine (T3). Amiodarone treatme nt typically results in a rise in serum T4, often to above the normal range, associated with a fall in circulating T3. These biochemical cha nges are found in subjects who remain clinically euthyroid. In additio n to changes in circulating thyroid hormones found in euthyroid subjec ts, overt thyrotoxicosis and hypothyroidism may complicate amiodarone treatment. Amiodarone-induced thyrotoxicosis is more common in areas o f iodine deficiency, whereas hypothyroidism is more common in iodine-r ich parts of the world.