Magnitude and time course of urinary iodine excretion in patients after amiodarone therapy

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.

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.

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.

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.