Influence of short-term interruption of antithyroid drugs on the outcome of radioiodine therapy of Graves' disease: Results of a prospective study

Aim: The factors influencing success of treating Graves' disease with radioiodine (I-131) are discussed controversially. This study analyses prospectively the influence of discontinuing antithyroid drugs (ATD) immediately prior to treatment with radioiodine on the therapeutic outcome. Methods: We studied 141 patients with Graves' disease. In 73 of them (group A) treatment was performed under medication with ATD, in 68 patients (group B) ATD were discontinued for 3-7 days starting at the time of therapy. We performed a statistical analysis of the influence of ATD and other factors potentially influencing treatment results. Results: In group A 49/73 patients were treated successfully (67%) vs. 58/68 (85%) in group B (p < 0.01). Characteristic changes in the kinetics of radioiodine were observed: after discontinuing ATD specific uptake was higher (2.0%/ml in group A vs. 2.6%/ml in group B, p = 0.004), and the effective half life was longer (5.1 +/- 1.3 d in group A vs. 5.5 +/- 1.1 d in group B, p = 0.076) resulting in a significantly higher radiation dose in group B (200 +/- 61 Gy in group A vs. 236 +/- 72 Gy in group B, p = 0.002). Conclusion: We conclude that short-term interruption of ATD improves the success rate of treating Graves' disease with radioiodine significantly.