The outcome of 131I treatment in Graves' patients pretreated or not with methimazole

Despite extensive use of iodine-131 (I-131) treatment for Graves' hyperthyroidism, the optimal regimen of pretreatment with antithyroid drugs is still a matter of discussion. Our aim was to evaluate the success of I-131 treatment in patients with Graves' disease without and with pretreatment with methimazole (MMI). In a prospective randomized study 156 patients with Graves' disease were treated with fixed activity of 550MBq I-131. First group of 59 patients received only I-131. The second group of 50 patients received MMI which was stopped seven days before I-131. The third group of 47 patients received MMI until I-131 application. Patients were followed clinically and biochemically 1, 3, 6 and 12 months after I-131 treatment. Absorbed dose of I-131 and thyroid volume were measured in each patient. Our result showed that I-131 treatment success after twelve months was equally effective in the first and second group (96.6% and 96%, respectively), while in the third group, success was significantly lower (63.8%). Accordingly, the absorbed dose of I-131 was significantly higher in the first and in second group (144 +/- 104Gy and 164 +/- 107Gy, respectively), and lower in the third group (105 +/- 58Gy) Thyroid volume gradually decreased without any significant difference between the three groups. In conclusion, our study provides evidence that application of I-131 is equally effective in the nonpretreated with MMI group and in the group discontinuing MMI one week before I-131 treatment, and it is more effective in these two groups as compared to the group in which pretreatment with MMI was administered till the day of I-131 application.