Continuous Methimazole Therapy and Its Effect on the Cure Rate of Hyperthyroidism Using Radioactive Iodine: An Evaluation by a Randomized Trial

Background: A randomized clinical trial was performed to clarify whether continuous use of methimazole (MTZ) during radioiodine (131I) therapy influences the final outcome of this therapy. Design: Consecutive patients with Graves’ disease (n = 30) or a toxic nodular goiter (n = 45) were rendered euthyroid by MTZ and randomized to stop MTZ 8 d before 131I (−MTZ; n = 36) or to continue MTZ until 4 wk after 131I (+MTZ; n = 39). Calculation of the 131I activity included an assessment of the 131I half-life and the thyroid volume. Results: The 24-h thyroid 131I uptake was lower in the +MTZ group than in the −MTZ group (44.8 ± 15.6% vs. 62.1 ± 9.9%, respectively; P < 0.001). At 3 wk after therapy, no significant change in serum free T4 index was observed in the +MTZ group (109 ± 106 vs. 83 ± 28 nmol/liter at baseline; P = 0.26), contrasting an increase in the −MTZ group (180 ± 110 vs. 82 ± 26 nmol/liter; P < 0.001). The number of cured patients was 17 (44%) and 22 (61%) in the +MTZ and −MTZ groups, respectively ...