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sodium iodide I 131, Iodotope, Sodium Iodide I 131 Therapeutic

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GENERIC NAME: sodium iodide I 131

BRAND NAME: Iodotope, Sodium Iodide I 131 Therapeutic

DRUG CLASS AND MECHANISM: Sodium iodide I 131 is an oral medication used to treat hyperthyroidism (overactive thyroid gland) and some cases of thyroid cancer. It falls under the category of an anti-thyroid agent but differs from propylthiouracil (PTU) and methimazole (Tapazole) because it is radioactive.

Sodium iodide I 131 is taken by mouth, readily absorbed into the body and is trapped within the thyroid gland. The trapped sodium iodide I 131 irradiates the thyroid gland thereby damaging it. As a result, the activity of the thyroid gland (that is, the release of thyroid hormone) is reduced. Excess sodium iodide I 131 is eliminated from the body in urine by the kidneys. The sodium iodide retained in the body loses most of its radioactivity over several weeks. (The half-life of the radioactivity is eight days.)

GENERIC AVAILABLE: no

PRESCRIPTION: yes

PREPARATIONS: Sodium iodide I 131 is available as a capsule containing 0.75-100 millicuries (mCi) of radioactivity per capsule. (A millicurie is a unit for measuring radioactivity.) It is also available as a liquid containing 7.05 mCi per milliliter in vials containing 7-106 mCi, or in vials containing 3.5-150 mCi.

STORAGE: Sodium iodide I 131 capsules and liquid are ordered for individual patients in a hospital setting. They arrive at room temperature in lead containers to minimize radiation exposure to hospital personnel. Special handling is required.

PRESCRIBED FOR: Sodium iodide I 131 is used to treat hyperthyroidism and some cases of thyroid cancer.

DOSING: The usual sodium iodide I 131 dose ranges from 4-10 mCi to treat hyperthyroidism. Doses to treat thyroid cancer are individualized and are usually 10-27 times greater than for hyperthyroidism.

DRUG INTERACTIONS: Non-radioactive iodine, thyroid hormone, propylthiouracil (PTU) or methimazole (Tapazole) may all interfere with the trapping of sodium iodide I 131 by the thyroid gland.

PREGNANCY: Sodium iodide I 131 has been shown to cause harm to a developing fetus. Use in pregnant women should be avoided.

NURSING MOTHERS: Iodine is excreted in breast milk. Therefore, formula feedings for infants are strongly recommended for nursing women requiring sodium iodide I 131 treatment.

SIDE EFFECTS: The side effects commonly seen with sodium iodide I 131 treatment are mild with the smaller doses given for hyperthyroidism but may be more severe with the larger doses given for thyroid cancer.

Sodium iodide I 131 may cause suppression of the bone marrow, resulting in anemia, and reductions in white blood cell count and platelets. It also may cause acute leukemia. With large doses, radiation sickness manifest by symptoms of nausea, vomiting, chest pain, increased heart rate, itchy skin, rash, hives and possibly death, also may occur. Thyroid crisis (due to the release of large amounts of thyroid hormone), severe inflammation of the salivary glands, and chromosomal abnormalities may occur. On day three after treatment, a constellation of signs and symptoms may occur including neck tenderness and swelling, pain with swallowing, sore throat and cough. Finally, temporary hair thinning may occur two to three months after treatment.

Reference: FDA Prescribing Information

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