Risk factor of amiodarone-induced hypothyroidism

Amiodarone (AMD), used to treat arrhythmia has an iodine content of 37%, therefore, it is believed that this drug may have adverse effects when administered in the early stages of thyroid gland development. Further, amiodarone-induced hypothyroidism (AIH) is frequently caused by chronic thyroiditis. In this study, we sought to elucidate the frequency of AIH and clarify the relation among sex, the age, the blood levels of AMD, the results of thyroid function tests, and the onset of AIH. Further, we determined the time and dosage at which levothyroxine sodium hydrate (LTN) therapy was initiated in patients with AIH. We investigated 372 cases, and LTN therapy was administered concurrently with other agents in 94 cases. The results revealed that AIH occurred frequently in young women. The results also showed that the onset of AIH was not influenced by the blood levels of amiodarone. In a number of cases, AIH was seen in cases in which the thyroid stimulating hormone (TSH) levels were high before AMD was administered. In patients with AIH, LTN was administered at a mean dose of 25 μ g for an average of 12-36 months. However, LTN seemed to be effective in normalizing the levels of TSH when administered at a dose of 50-100 μ g. Therefore, it was thought that it was desirable to observe a thyroid gland function carefully in cases where the TSH level was high before the initiation of AMD therapy.