Sodium iodide I 131 (Oral route)


SOE-dee-um EYE-oh-dide I 131

Brand Names:

  • Iodotope

Dosage Forms:

  • Kit



Diagnostic Agent, Radiopharmaceutical Imaging

Uses of This Medicine:

Sodium iodide I 131 is used to treat hyperthyroidism (an overactive thyroid) and certain kinds of thyroid cancer. This medicine is taken up mainly by the thyroid gland. In the treatment of overactive thyroid gland, the radiation from the radioactive iodine damages the thyroid gland to bring its activity back down to normal. Larger doses of radioiodide are usually used after thyroid cancer surgery to destroy any remaining diseased thyroid tissue or to destroy thyroid cancer that has spread to other tissues.

When very small doses are given, a measure of the radioactivity taken up by the gland helps your doctor decide whether your thyroid gland is working properly or to locate tumors caused by certain types of thyroid cancers.

This medicine is to be given only by or under the direct supervision of a doctor with specialized training in nuclear medicine or radiation oncology.

Before Using This Medicine:

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies have not been performed on the relationship of age to the effects of sodium iodide I 131 capsules or solution in the pediatric population. Safety and efficacy have not been established.

Older adults—

Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of sodium iodide I 131 capsules or solution in the elderly. However, elderly patients are more likely to have age-related kidney or heart problems, which may require caution and an adjustment in the dose for patients receiving sodium iodide I 131 capsules or solution.


Studies in women breastfeeding have demonstrated harmful infant effects. An alternative to this medication should be prescribed or you should stop breastfeeding while using this medicine.

Other medicines—

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

Other interactions—

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other medical problems—

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Asthma or
  • Sulfite allergy, history of—This medicine contains sodium bisulfite, which can make these conditions worse.
  • Diarrhea or vomiting or
  • Thyroid cancer, medullary or anaplastic—Should not be used in patients with these conditions unless determined by your doctor.
  • Heart disease or
  • Neck or throat blockage problems (eg, esophagus, trachea, or blood vessels in the neck)—Use with caution. May make these conditions worse.
  • Kidney disease—Use with caution. The effects may be increased because of slower removal of the medicine from the body.

Proper Use of This Medicine:

Before receiving this medicine, make sure you understand all the risks and benefits. It is important for you to work closely with your doctor during your treatment.

A nurse or other trained health professional will give you this medicine in a hospital or clinic. It is given by mouth.

Your doctor may have special instructions for you to get ready for your treatment. If you have not received such instructions or you do not understand them, check with your doctor ahead of time.

Precautions While Using This Medicine:

Your doctor will check your progress closely while you are receiving this medicine. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to receive it. Blood and urine tests may be needed to check for unwanted effects.

Using this medicine while you are pregnant can harm your unborn baby. If you are a woman who can bear children, your doctor may give you a pregnancy test before you start receiving this medicine to make sure you are not pregnant. You must use two forms of birth control together for at least 6 months after using this medicine. Use birth control pills together with another form of birth control, such as a condom, diaphragm, or contraceptive foam or jelly. If you think you have become pregnant while using the medicine, tell your doctor right away.

If you are receiving sodium iodide I 131 for an overactive thyroid or cancer of the thyroid, your doctor may tell you to follow some or all of these guidelines for 48 to 96 hours after receiving the medicine, to help reduce the chance of contaminating other persons:

  • Do not kiss anyone, or handle or use another person's eating or drinking utensils, toothbrush, or bathroom glass.
  • Do not have sex.
  • Do not sit close to others, especially pregnant women, and do not hold children in your lap for long periods of time.
  • Sleep alone.
  • Wash the tub and sink after each use (including after brushing teeth).
  • Wash your hands after using or cleaning the toilet.
  • Use a separate towel and washcloth.
  • Wash your clothes, bed linens, and eating utensils separately.
  • Sodium iodide I 131 is passed in the urine. To prevent contamination of your home, flush the toilet twice after you urinate.

If you were treated with sodium iodide I 131 for an overactive thyroid, your doctor may want to check the level of thyroid hormone in your blood every 2 to 3 months during the first year, and once a year thereafter. This is to make sure that your thyroid has not become underactive.

This medicine may cause allergic reactions. Check with your doctor right away if you have a rash, hives, itching, fast heartbeat, shortness of breath, or swelling of the eyes, face, lips after receiving the medicine.

This medicine may increase your risk for cancer or thyroid problems. Talk with your doctor about these risks. You may need to take other medicine with this medicine to prevent thyroid problems.

You will be exposed to dangers of radiation while using this medicine. Talk to your doctor about this risk and the precautions that you might need to take.

This medicine might cause temporary infertility in both men and women. Discuss this with your doctor if you plan to have children.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Side Effects of This Medicine:

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur:

After treatment of overactive thyroid
Symptoms of an underactive thyroid
Changes in menstrual periods
dry, puffy skin
muscle aches
thinning of the hair (temporary)
unusual tiredness or weakness
weight gain
After treatment of overactive thyroid
Excessive sweating
fast, irregular, pounding, or racing heartbeat or pulse
unusual irritability
After treatment of cancer of the thyroid
Black, tarry stools
blood in the urine or stools
cough or hoarseness
fever or chills
lower back or side pain
painful or difficult swallowing
painful or difficult urination
pinpoint red spots on the skin
unusual bleeding or bruising
Incidence not known
After treatment of overactive thyroid
Chest pain
fast, pounding, or irregular heartbeat or pulse
hives, itching, and rash
sensitivity to heat
tenderness of salivary glands
trouble sleeping
weight loss
After treatment of cancer of the thyroid
Abdominal or stomach cramps
bleeding gums
bone pain
feeling of discomfort
loss of appetite
sore throat
unusual tiredness or weakness

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common
After treatment of overactive thyroid or cancer of the thyroid
Neck tenderness or swelling
sore throat
After treatment of cancer of the thyroid
Loss of taste (temporary)
nausea and vomiting (temporary)
tenderness of the salivary glands

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Last Updated: 6/10/2021
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