Side Effects of Sodium Iodide I 131

Sodium iodide I 131 is an oral anti-thyroid drug used to treat hyperthyroidism (overactive thyroid gland) and some cases of thyroid cancer.

• It differs from the other anti-thyroid drugs, propylthiouracil (PTU) and methimazole (Tapazole), because it is radioactive.
• Sodium iodide I 131 is taken orally, readily absorbed into the body and is trapped within the thyroid gland.
• The trapped sodium iodide I 131 irradiates the thyroid gland and damages it, resulting in a reduction in the activity of the thyroid gland.
• 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. 

Common side effects of sodium iodide I 131 include:

• nausea,
• vomiting,
• chest pain,
• increased heart rate,
• itchy skin,
• rash,
• hives, and
• temporary hair thinning.

Serious side effects of sodium iodide I 131 include:

• thyroid crisis,
• severe inflammation of the salivary glands, and chromosomal abnormalities,
• suppression of the bone marrow resulting in anemia and reductions in white blood cells and platelets,
• acute leukemia, and
• possibly death.

Drug interactions of sodium iodide I 131 include non-radioactive iodine, thyroid hormone, propylthiouracil or methimazole, which may all interfere with the trapping of sodium iodide I 131 by the thyroid gland.

Thyroid hormone, drugs that contain iodine, 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. Formula feedings for infants are strongly recommended for breastfeeding women requiring sodium iodide I 131 treatment.

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.

Although rare, reactions associated with the administration of iodine containing radiopharmaceuticals for diagnostic use include, in decreasing order of frequency:

• nausea,
• vomiting,
• chest pain,
• tachycardia,
• itching skin,
• rash and
• hives.

No information provided.