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 drug but differs from the other anti-thyroid drugs, 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 production and release of thyroid hormone) is reduced. Excess sodium iodide I 131 is eliminated from the body in the 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. The FDA approved sodium iodide I 131 in August 1971.

Sodium Iodide I 131 Therapeutic, Hicon

GENERIC AVAILABLE: Yes

Yes

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 cells and platelets. It also may cause acute leukemia.

Other important side effects that can occur with large doses include symptoms of:

• nausea,
• vomiting,
• chest pain,
• increased heart rate,
• itchy skin,
• rash,
• hives, and
• possibly death.

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.

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.

Non-radioactive iodine, thyroid hormone, propylthiouracil (PTU) or methimazole (Tapazole, Northyx) may all interfere with the trapping of sodium iodide I 131 by the thyroid gland. Thyroid hormone, drugs that contain iodine (for example, amiodarone [Coradone]), and iodine containing contrast agents all interfere with the action of sodium iodide I 131.

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

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

What preparations of sodium iodide I 131 are available?

Capsules; with radioactivity of 0.75 to 100 mCi per capsule. (A millicurie is a unit for measuring activity). Sodium iodide I 131also is available as a liquid in vials containing 5 to 150 mCi/vial.

How should I keep sodium iodide I 131 stored?

Sodium iodide I 131 should be store at room temperature, 20-25 C (68-77 C). Sodium iodide I 131 is ordered for individual patients in a hospital setting. It arrives at room temperature in a lead container to minimize radiation exposure to hospital personnel. Special handling is required.