The Accumulation of35S-Antithyroid Drugs by the Thyroid Gland

Accumulation of 35S-radioactivity by the thyroid gland was found after administration of equimolar doses of 35S-labelled thiouracil, methylthiouracil, propyl thiouracil, methimazole and carbimazole to rats. Thin-layer chromatography showed an accumulation of the parent drug in the case of methimazole, propylthiouracil, methylthiouracil and thiouracil. When carbimazole was given, an accumulation of methimazole was demonstrated in the thyroid. Propylthiouracil administration produced the largest amount of drug in the thyroid and thiouracil the least. In man both 35S-radioactivity and the parent drug accumulated in the normal thyroid after administration of methimazole and propylthiouracil. When carbimazole was given, methimazole accumulated in the thyroid. In six thyroid tumors little or no accumulation of the antithyroid drug was found.