The Effect of Small Doses of Stable Iodine in Patients with Hyperthyroidism

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Abstract
The effect of small doses of iodine has been studied in 34 hyperthyroid and 11 euthyroid persons, using the protein-bound iodine level as the major index. Seventeen hyperthyroid patients received iodine, 1 mg daily, for variable periods. In 12 of these, there was evidence of thyroid inhibition as judged by clinical observations and decreased serum protein-bound iodine concentrations, while in the remainder no beneficial effect was observed. In all of 13 hyperthyroid patients given 2 mg of iodine daily, and in two patients given 4 mg of iodine daily, an inhibition of thyroid activity was observed. In the patients who exhibited this response to either 1, 2, or 4-mg daily doses of iodine, improvement was apparent within 48 hours. In those patients who continued on this therapy for several weeks, there was usually a tendency towards the end of the period for the protein-bound iodine to rise above its lowest level, suggesting an escape from the influence of iodine. Thyrotropin (THS) was administered to 4 hyperthyroid patients during this study, Two mg of iodine were given daily to 2 patients on the last 4 days of an 8-day period of administration of thyrotropin. In both, the protein-bound iodine fell promptly despite the continued administration of exogenous thyrotropin. This was given to a third patient in whom the administration of 1 mg of iodine daily had produced a steady fall in the serum protein-bound iodine; a small rise in this value followed the administration of thyrotropin. In a fourth patient who had responded well on 2 mg of iodine daily, the administration of thyrotropin during the period of inhibition had no apparent effect. In 11 euthyroid persons, the administration of such small doses of iodine failed to affect the protein-bound iodine. In two other euthyroid persons whose protein-bound iodine had risen during stimulation with thyrotropin, the minute doses of iodine had no effect on levels of this value. It is apparent that small doses of iodine have a pronounced effect on the levels of protein-bound iodine in hyperthyroidism, and that the much larger doses often used clinically are unnecessarily high. The administration of 1-mg doses of iodine usually, but not always, has a beneficial effect. Two-mg doses were effective in all patients studied, but did not always bring the protein-bound iodine to euthyroid levels. In both hyperthyroid patients given daily doses of 4 mg of iodine, the protein-bound iodine fell to normal. Doses from 2 to 4 mg of iodine daily are optimal for some people, but not for all; a dosage of 4 to 6 mg would probably suffice for the great majority of hyperthyroid patients.