Treatment of hyperthyroidism with a small single daily dose of methimazole: a prospective long-term follow-up study

A prospective long-term follow-up study was performed with conventional divided doses (group C: 10 mg 3 times daily, N = 58) and a small single daily dose (group S: 15 mg once daily, N = 54) of methimazole (MMI) for the treatment of Graves' hyperthyroidism. Within 8 weeks, almost 80% of the patients in both groups became euthyroid. The mean time required to achieve a euthyroid state was 5.6 +/- 2.7 weeks in group C and 5.8 +/- 3.1 in group S. TSH binding inhibitor immunoglobulin (TBII) levels before therapy were 44.2 +/- 22.7% and 47.1 +/- 23.9% in group C and group S, respectively. A similar gradual fall in TBII levels was observed in both groups over a two-year period of treatment. MMI doses were gradually reduced to a maintenance dose (5 mg daily) after the patients became euthyroid. The patients were treated for 28 +/- 9 months and were followed up after therapy was stopped (observation period in patients who remained in remission was 12-130 (75 +/- 34) months and the interval to relapse in recurred cases was 1-98 (20 +/- 27) months). The rates of recurrence in group C were 41% at 1 yr, 54% at 2 yrs, 56% at 4 yrs and 61% at 6 yrs. In group S, these were 44%, 53%, 56% and 63%, respectively. No differences between relapse rates were observed with the two different dosage regimens. Adverse effects occurred more frequently in group C patients (24%) than in group S patients (13%). These results show that there is no difference in the clinical and immunological course or in the long-term remission rate of Graves' hyperthyroidism when the treatment is initiated with either a small single daily dose (15 mg) or the conventional regimen (10 mg 3 times daily).