Effects of propylthiouracil and relatively small doses of iodide on early phase treatment of hyperthyroidism.

In order to compare the acute effects of three methods of treatment in hyperthyroid patients with diffuse goitre, values of thyroxine (T4), triiodothyronine (T3) in serum, T3-resin uptake (T3-U), free thyroxine index (FT4I) and free triiodothyronine index (FT3I) were employed as thyroid function parameters. In iodide (I-) group given iodine (3 or 6 mg/day) as iodinated lecithine once daily, the parameters were reduced acutely within one week after the start of treatment, reaching a plateau during the next week. In contrast to the changes in I- group, the thyroid function was decreased gradually and consistently for two weeks in the propylthiouracil (PTU 300 mg/day) group. In PT1+I- (300 mg/PTU plus 3 or 6 mg/iodide/day) group, the parameters were reduced acutely and progressively for two weeks. These results indicate that PTU+I- therapy is much more effective than PTU or I- alone in early phase treatment of hyperthyroidism. Another new finding was that the thyroid function increased again during the later addition of PTU (300 mg/day) in the patients treated with I- (3 or 6 mg/day) for one or two weeks. The well-known escape phenomenon from iodide inhibition took place counteracted the effect of PTU. Since blocking of thyroidal secretion by I- is only transient while synthesis of T3 and T4 continues, leading to greater amount of hormone stored in the gland, the treatment of hyperthyroidism with I- alone is a risky procedure.