Radioiodine

An isotope of the chemical element iodine that is radioactive. Radioiodine is used in diagnostic tests as well as in radiotherapy of an hyperactive thyroid gland (hyperthyroidism), most often due to Graves disease. For hyperthyroidism, radioiodine is administered in capsule form on a one- time basis. It directly radiates thyroid tissues, thereby destroying them. It takes 8-12 weeks for the thyroid to become euthyroid (normal) after treatment. The majority of patients undergoing this treatment eventually become hypothyroid, which is easily treated using thyroid hormones (levothyroxine). Radioiodine should not be used during pregnancy or breast feeding. Radioiodine is the preferred initial therapy for the hyperthyroidism of Graves disease in North America while antithyroid drugs are used as the first line of treatment in most of the rest of the world.

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A radioactive isotope of iodine; e.g., ¹²³I.

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ra·dio·io·dine -'ī-ə-.dīn, -əd-ən, -ə-.dēn n radioactive iodine esp IODINE-131

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ra·dio·io·dine (ra″de-o-iґo-dīn) any of the nine radioactive isotopes of iodine; ¹³¹I, ¹²⁵I, and ¹²³I are the most commonly used in the diagnosis and treatment of both benign and malignant disease of the thyroid gland and in the scintiscanning of such organs as the lung, liver, and kidney.