Resumption of methimazole after 131I therapy of hyperthyroid diseases: effect on thyroid function and volume evaluated by a randomized clinical trial.
OBJECTIVE
Retrospective studies have indicated that anti-thyroid drugs (ATD) might possess a radioprotective effect, leading to a higher rate of recurrence of hyperthyroidism after iodine-131 ((131)I) therapy.


METHODS
A randomized clinical trial was performed to clarify whether resumption of methimazole after (131)I influences the final outcome of this treatment.


METHODS
We assigned 149 patients with Graves' disease or a toxic nodular goitre to groups either to resume (+ATD) or not to resume (-ATD) methimazole 7 days after (131)I. Before (131)I therapy, all patients were rendered euthyroid by methimazole, which was discontinued 4 days before the (131)I therapy.


RESULTS
During the follow-up period of 12 Months, 13 patients developed hypothyroidism, 42 were euthyroid, and 18 had recurrence of hyperthyroidism in the +ATD group; the respective numbers in the -ATD group were 16, 42 and 18 (P=0.88). At 3 weeks after (131)I therapy, the serum free-thyroxine index was slightly decreased (by 5.7%; 95% confidence interval (CI) -15.5 to 5.4%) in the +ATD group, in contrast to an increase of 35.9% (95% CI 18.8 to 55.5%) in the -ATD group (P<0.001 between groups). In the subgroup that remained euthyroid during follow-up, thyroid Volume reduction, assessed by ultrasonography, was smaller in the +ATD group [38.7% (95% CI 33.3 to 44.1%)] than in the -ATD group [48.6% (95% CI: 41.5-55.6%)] (P<0.05).


CONCLUSIONS
No radioprotective effect could be demonstrated, with regard to final thyroid function, for the resumpton of methimazole 7 days after (131)I therapy. Although resumption of methimazole slightly reduced the magnitude of shrinkage of the goitre obtained by (131)I, the prevention of a temporary thyrotoxicosis in the early period after radiation favours this regimen.
Bonnema
Steen J
SJ
Department of Endocrinology, Odense University Hospital, DK-5000, Odense, Denmark. steen.bonnema@dadlnet.dk
Bennedbaek
Finn N
FN
Gram
Jeppe
J
Veje
Annegrete
A
Marving
Jens
J
Hegedus
Laszlo
L
D000368:Aged; D013956:Antithyroid Agents / Q000627:therapeutic use; D003131:Combined Modality Therapy; D005260:Female; D005500:Follow-Up Studies; D006044:Goiter, Nodular / Q000188:drug therapy* / Q000532:radiotherapy*; D006111:Graves Disease / Q000188:drug therapy* / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008713:Methimazole / Q000627:therapeutic use*; D008875:Middle Aged; D011837:Radiation-Protective Agents / Q000627:therapeutic use*; D012008:Recurrence; D016896:Treatment Outcome
D013956:Antithyroid Agents; D007457:Iodine Radioisotopes; D011837:Radiation-Protective Agents; D008713:Methimazole