Thyroid Hormone & Antithyroid Agents 295The iodinated contrast agents, ipodate
and iopanic acid are used in the treatment
of hyperthyroidism. These drugs rapidly
inhibit the conversion of T 4 to T 3 in the liver,
kidney, brain and pituitary gland.
Agents Which Destroy Thyroid Gland
Tissue
(^131) I is the only radioisotope of iodine
used in the treatment of thyrotoxicosis. The
other isotopes^123 I and^125 I are used only in
diagnosis.^131 I emits gamma and beta radia-
tions. It is available as sodium solution.
When taken orally, it is rapidly absorbed,
concentrated by the thyroid and incorporat-
ed into the storage follicles. Beta radiation
penetrates up to 3 to 5 mm into the soft
tissue, they destroy some of the thyroid
follicles and produce fibrosis.
Adverse reactions include hypothyroid-
ism, thyroid carcinoma, damage to foetal
thyroid and possibility of genetic damage, so
contraindicated during pregnancy.
Radioactive iodine is indicated in
hyperthyroidism due to Graves’ disease or
toxic nodular goitre and also used as
palliative therapy after thyroidectomy for
papillary carcinoma of thyroid.