Effect of iodine administration on thyroid function in diabetic patients.

Iodide-induced hypothyroidism has been observed in subjects treated with compounds with mild antithyroid activity. The hypoglycemic agent tolbutamide belongs to the aminoheterocyclic group, a class of compounds with antithyroid effect. Thus it was thought interesting to study the effect of large doses of iodide on thyroid function in diabetics chronically treated with tolbutamide. Basal thyroid function as assessed by clinical examination and iodothyronine and TSH concentrations was normal in all patients. Furthermore, in diabetics treated with tolbutamide, hormone concentrations were not different from those of patients treated with insulin or diet. Serum T4, T3 and TSH did not show any significant variation throughout the investigation period. Our results suggest that thyroid function is not affected by chronic treatment with tolbutamide even when large doses of iodide are administered.