Effects of long-term amiodarone treatment on thyroid function.

Serum determinations of total T4, total T3, reverse T3, free T3 index, free T4, free T4 index, TBG, T4/TBG ratio, TSH and cholesterol were carried out on 18 euthyroid patients with coronary heart disease. Serum samples were obtained before treatment and after 15 days, 2, 4, 6, 8, 10, 12, 14 and 16 months of treatment with amiodarone (400 mg/day). Patients were divided into two groups, according to patterns of TSH response to thyrotrophin-releasing hormone (TRH): (I) patients with normal responses (n = 12), and (II) patients with subnormal responses (n = 6). Patients of group I showed total T4, free T4 and reverse T3 increments and total T3 and free T3 index decreases, whereas patients of group II were distinguished by the absence of T3 decreases and a rise in free T4 levels that showed a significant correlation with a drop in serum cholesterol (r = -0.767; p. less than 0.001). No patient of either group showed clinical signs of thyroid dysfunction. These results show that the appearance of hormonal patterns of hyperthyroidism is unpredictable and very frequent in patients with no previous thyroid abnormalities undergoing long-term treatment with the drug.