Magnitude and time course of urinary iodine excretion in relation to thyroid function in patients on amiodarone therapy

Abstract

Purpose. Amiodarone is a source of excess iodine that may induce thyroid dysfunction. The aim of the present analysis was to evaluate the magnitude and time course of 24-hr urinary iodine excretion and its potential relationship with thyroid disorders in patients on antiarrhythmic prophylaxis with amiodarone. Methods. 24-hr urinary iodine excretion and thyroid function were evaluated in 67 patients on chronic amiodarone therapy. All patients were clinically and biochemically euthyroid before starting treatment and were followed up by 6-month measurements of 24-hr urinary iodine excretion and plasma TSH levels. Results. Since amiodarone initiation, 20 patients developed thyroid dysfunction (14 hypothyroidism, 3 subclinical hypothyroidism, 3 hyperthyroidism). No differences were observed in terms of treatment length or urinary iodine levels between patients remaining euthyroid and those developing thyroid dysfunction: urinary iodine in the euthyroid group was 8094 µg/24h (IQR 4082-10766) vs 10851 µg/24h (IQR 8529-12804) in the thyroid dysfunction group at 6 months (p = 0.176) and 8651 µg/24h (IQR 6924-11574) vs 8551 µg/24h([IQR 4916-13580) (p = 0.886) at one year from amiodarone initiation. The occurrence of thyroid dysfunction was equally distributed among patients taking amiodarone for more than one year versus those under treatment for less than one year. Upon amiodarone withdrawal, normal range of urinary iodine was achieved after a mean time of 15.2 ± 7.7 months. Conclusion. These results suggest no correlation between 24-hr urinary iodine excretion and thyroid dysfunction in patients on amiodarone therapy. Thyroid disorders following amiodarone administration likely depend on the individual predisposition to iodine load.