Background: Amiodarone is a source of iodine excess that may persist in the body for long time after its withdrawal. The aim of the present analysis was to evaluate the magnitude and long-term time course of 24-h urinary iodine (UI) excretion in patients on antiarrhythmic therapy with amiodarone.
Methods: 24-h UI excretion and thyroid function were evaluated in 67 patients on amiodarone therapy. All patients were clinically and biochemically euthyroid before starting treatment and were followed-up by 6-month measurements of 24-h UI excretion and plasma thyroid hormones levels.
Results: Upon amiodarone withdrawal, normal range of UI was achieved after a mean time of 15.2±7.7 months. Since amiodarone initiation, 20 patients developed thyroid dysfunction. No differences were observed in terms of treatment length or median UI levels between patients remaining euthyroid and those developing thyroid dysfunction: median UI in the euthyroid group was 8094 µg/24 h (Interquartile Range [IQR]: 4082-10766) vs. 10851 µg/24 h (IQR: 8529-12804) in the thyroid dysfunction group at 6 months (P=0.176) and 8651 µg/24 h (IQR: 6924-11574) vs. 8551 µg/24 h (IQR: 4916-13580) at one year from amiodarone initiation (P=0.886). 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.
Conclusions: These results confirm the long-lasting total-body iodine stores and consequent excretion in patients after amiodarone withdrawal. These long-lasting iodine stores might be taken into special account in patients necessitating therapy with radioactive iodine and for long-term monitoring of thyroid function after amiodarone discontinuation.