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A randomized trial evaluating a block-replacement regimen during radioiodine therapy


  • Identifier: NCT00150124

  • Randomized clinical trial

Steen J. Bonnema, Consultant, MD, PhD, Department of Endocrinology, Odense University Hospital, DK-5000 Odense C, Denmark. Tel.: +45-65413437; fax: +45-65919653; e-mail:


Eur J Clin Invest 2010; 41 (7): 693–702


Background  Lack of consensus regarding the antithyroid drug regimen in relation to radioiodine (131I) therapy of hyperthyroidism prompted this randomized trial comparing two strategies.

Design  Patients with Graves’ disease (GD, n = 51) or toxic nodular goitre (TNG, n = 49) were randomized to 131I either 8 days following discontinuation of methimazole (−BRT, n = 52, median dose: 5 mg) or while on a continuous block-replacement regimen (+BRT, n = 48, median dose 15 mg methimazole and 100 μg levothyroxine).

Results  Patients in the +BRT group required more radioactivity. In this group, thyroid function did not change in the early post 131I period, while serum-free T3 index was higher in the −BRT group (P < 0·05). One year posttherapy, the fraction of cured patients (euthyroid or hypothyroid) was 48% and 61% in the +BRT and −BRT group, respectively (P = 0·014 unadjusted; P = 0·004 adjusted), but the outcome depended on the type of disease. In GD, treatment failure in the +BRT group correlated positively with the 24-h thyroid 131I uptake (P = 0·017), while no correlations existed in the −BRT group. In addition to +BRT allocation, patients with TNG were at higher risk of treatment failure with lower thyroid radiation doses (P = 0·048), higher doses of methimazole (P = 0·026) and lower levels of serum TSH (P = 0·009).

Conclusions  A continuous block-replacement regimen results in a stable thyroid function during 131I therapy but is hampered by the higher amounts of radioactivity required. The study demonstrates that the outcome in GD is highly unpredictable, while treatment failure in patients with TNG is correlated with a number of factors.