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Thyroid Medications (cont.)

Radioactive Iodine

131-iodine (131I or I-131) is the radioactive isotope used to kill both normal and cancerous thyroid cells

  • This is not to be confused with I-123, a harmless isotope used by radiologists in imaging and to determine thyroid activity
  • Radioactive iodine is safe to use in people who have allergic reactions with other iodine-containing compounds, including seafood and intravenous (IV) contrast media
  • The amount of elemental iodine in radioactive iodine is smaller than that in our daily diet

The three major uses for I-131 therapy

  1. hypothyroidism
  2. thyroid cancer
  3. toxic multinodular goiter

1) Hyperthyroidism

  • I-131 can be given to patients who have overactive thyroid tissue or enlarged thyroid glands to destroy normal thyroid tissue
  • Typically, the I-131 takes several months to have its full effect for eliminating the thyroid tissue

2) Thyroid cancer

  • Larger doses of I-131 are used to kill thyroid cancer cells

3) Nontoxic multinodular goiter

  • Used in Europe to shrink multinodular goiters by about 40%, but not typically used in the United States

Side effects are rare and easily treatable and include nausea, and pain or swelling of the thyroid tissue and salivary glands

Safety of radioactive iodine I-131

  • I-131 should never be used in women who are pregnant;
  • Pregnancy should be deferred by 6 months after I-131 therapy;
  • Long-term fertility is not affected in either men or women;
  • For lower doses of I-131 used for hyperthyroidism, the Nuclear Regulation Commission does not require isolation; still, general exposure to children and pregnant women should be avoided for 3 days after the treatment;
  • For larger doses of I-131 used in thyroid cancer patients, exposure to children and pregnant women should be avoided for 3 to 7 days after the treatment; and
  • Exposure of others to the body fluids (saliva, urine, nasal secretions, etc.) of a patient who has been recently treated with I-131 should be limited or avoided completely.

Medically reviewed by John A. Seibel, MD; Board Certified Internal Medicine with a subspecialty in Endocrinology & Metabolism


"Thyroid hormone action"

Medically Reviewed by a Doctor on 12/2/2015

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