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\u92 disease (n =3D 30) or a toxic nodular goiter (n =3D 45) were rendered euthyroid by MTZ and randomized to stop MTZ 8 d before 131I (-MTZ; n =3D 36) or to continue MTZ until 4 wk after 131I (+MTZ; n =3D 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 \ub1 15.6% vs. 62.1 \ub1 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 \ub1 106 vs. 83 \ub1 28 nmol/liter at baseline; P =3D 0.26), contrasting an increase in the -MTZ group (180 \ub1 110 vs. 82 \ub1 26 nmol/liter; P < 0.001). The number of cured patients was 17 (44%) and 22 (61%) in the +MTZ and -MTZ groups, respectively (P =3D 0.17). Cured patients tended to have a lower 24-h thyroid 131I uptake (50.1 \ub1 13.8% vs. 56.4 \ub1 17.1%; P =3D 0.09). By adjusting for a possible interfactorial relationship through a regression analysis (variables: randomization, 24- and 96-h thyroid 131I uptake, type and duration of disease, age, gender, presence of antithyroid peroxidase antibodies, thyroid volume, dose of MTZ), only the continuous use of MTZ correlated with treatment failure (P =3D 0.006), whereas a low 24-h thyroid 131I uptake predicted a better outcome (P =3D 0.006). Conclusion: Continuous use of MTZ hinders an excessive increase of the thyroid hormones during 131I therapy of hyperthyroid diseases. However, such a strategy seems to reduce the final cure rate, although this adverse effect paradoxically is attenuated by the concomitant reduction of the thyroid 131I uptake