Thyroid Research Thyroid Research Archive Hyperthyroidism

In hyperthyroidism therapy with methimazole after therapy with radioiodine does not reduce the efficacy of radioiodine

(March 2004)

The background of the study. Some patients with hyperthyroidism treated with iodine-131 (I-131) are then given an antithyroid drug, but there has been concern that the drug may reduce the efficacy of I-131. This study compared the effects of methimazole or no drug therapy given after I-131 in patients with hyperthyroidism.

How the study was done. The study subjects were 149 patients with hyperthyroidism caused by a toxic multinodular goiter, Graves’ disease, or a thyroid adenoma. They were treated with methimazole for at least three months, and were then given I-131 (average dose, 10.8±4.2 mCi [400±154 MBq]). Seven days later, the patients were randomly assigned to resume methimazole therapy or to receive no drug therapy. Thyroid function was assessed periodically for one year after I-131 therapy.

The results of the study. The patients in the two groups were similar in age, causes of hyperthyroidism, thyroid volume, serum thyroid hormone values, and 24-hour thyroid I-131 uptake values. At the end of the follow-up period, 84 patients (56 percent) were normal, 29 (20 percent) had hypothyroidism, and 36 (24 percent) had persistent hyperthyroidism. There were no differences in outcome in the methimazole and no-drug-therapy groups.

The conclusions of the study. Among patients with hyperthyroidism, therapy with methimazole after I-131 therapy does not alter the action of I-131.

The original article. Bonnema SJ, Bennedbaek FN, Gram J, Veje A, Marving J, Hegedus L. Resumption of methimazole after ¹³¹I therapy of hyperthyroid diseases: effect on thyroid function and volume evaluated by a randomized clinical trial. Eur J Endocrinol 2003;149:485-92.