Further Studies on the Long-Term Treatment of Graves' Hyperthyroidism with Ipodate: Assessment of a Minimal Effective Dose

Abstract

We have previously described that sodium ipodate (500 mg/day, p.o.) is effective in normalizing serum T₃ and T₄ levels in most patients with Graves' hyperthyroidism. In this study, we examined serum T₃, T₄, and rT₃ levels in 14 hyperthyroid patients with Graves' disease during treatment with a lower dose (500 mg, every other day, p.o.) of sodium ipodate for a period of 3-30 weeks (mean 15.5 weeks). Three types of responses were observed. In group I (4 patients), both serum T₃ and T₄ were in the normal range at the end of treatment [baseline: mean ± SEM T₃, 6.8 ± 0.96 nmol/L (normal 0.92-3.0)] and T₄ [256 ± 44 nmol/L (normal 62-167); post-ipodate: T₃, 2.0 ± 0.46 nmol/L and T₄ 107 ± 28 nmol/L]. In group II (n = 5), either serum T₃ (3 patients) or serum T₄ (2 patients) did not become normal (baseline: T₃ 7.7 ± 1.1 and T₄ 228 ± 3.9; post-ipodate: T₃ 2.9 ± 0.57 and T₄ 188 ± 27 nmol/L). In group III (5 patients), neither serum T₃ nor serum T₄ returned to normal following ipodate treatment (baseline: T₃ 11.9 ± 1.8 and T₄ 260 ± 23; post-ipodate: T₃ 7.5 ± 0.49 and T₄ 322 ± 17 nmol/L). The mean serum rT₃ concentration increased during ipodate treatment to a peak value of 100% above baseline and remained elevated (20-75% above baseline) throughout the study. Some improvement in hyperthyroidism was suggested by increase in body weight during ipodate treatment in most cases. The average body weight of patients increased by a maximum of 2.7 ± 0.7 kg at week 2, and the pulse rate diminished from the mean baseline value of 101 ± 3.1/min to a nadir value of 84 ± 2.8/min at week 3(p < 0.01). At the end of treatment, however, only group I patients (4 of 14, or 29%) demonstrated significant reduction in resting pulse rate (p < 0.05). Treatment of Graves' disease with 500 mg every other day of sodium ipodate results in infrequent normalization of serum thyroid hormone levels or clinical features of hyperthyroidism. The minimal effective dose of sodium ipodate for treating hyperthyroidism is more than 500 mg every other day and probably close to 500 mg/day.