Sodium Iodide I-131

Reviewed on 6/29/2022

What Is Sodium Iodide I-131and How Does It Work?

Sodium Iodide I-131 is a radioactive medication used for the treatment of hyperthyroidism and selected cases of thyroid cancer and as a diagnostic material for assessing thyroid function.

  • Sodium Iodide I-131 is available under the following different brand names: Hicon

What Are Dosages of Sodium Iodide I-131?

Adult dosage

Concentrated oral solution (diagnostic)

  • 5 mCi/mL (millicuries/mL; 185 MBq)
  • 25 mCi/mL (925 MBq)

Concentrated oral solution (therapeutic)

  • 185-5550 MBq /vial (5-150 mCi) iodine-131 at the time of calibration

Capsule (diagnostic)

  • 15 microCT (0.555 MBq)
  • 25 microCT (0.925 MBq)
  • 50 microCT (1.85 MBq)
  • 100 microCT (3.7 MBq)

Capsule (therapeutic)

  • 0.75-100 mCi (28-3700 MBq)

Hicon kits (therapeutic)

  • 250 mCi/0.25mL (9500 MBq [9.25 GBq])
  • 500 mCi/0.5mL (18.5 GBq)

1000 mCi /mL (37 GBq)

Hyperthyroidism Treatment

Adult dosage

  • 4-10 mCi PO (148-370 MBq)

Thyroid Cancer

Adult dosage

  • Ablation of normal thyroid tissue: Initial dose of 30-100 mCi PO (1100-3700 MBq)
  • Subsequent metastases ablation: 100-200 mCi orally (3700-7400 MBq)

Thyroid Function Diagnostic

Adult dosage

  • Thyroid uptake: 5-15 micro C orally (0.185-0.555 MBq)
  • Scintiscanning: 50-100 microCi orally (1.85-3.7 MBq)
  • Localization of extra-thyroidal metastases: 1000 micro C orally (37 MBq)

Dosage Considerations – Should be Given as Follows: 

  • See “Dosages”

What Are Side Effects Associated with Using Sodium Iodide I-131?

Common side effects of Sodium Iodide I-131 include:

  • changes in menstrual periods
  • clumsiness
  • coldness
  • drowsiness
  • dry, puffy skin
  • headache
  • listlessness
  • muscle aches
  • thinning of the hair (temporary)
  • unusual tiredness or weakness
  • weight gain

Serious side effects of Sodium Iodide I-131 include:

  • hypersensitivity
  • severe allergic reaction (anaphylaxis)
  • rash
  • hives
  • bronchospasm, and
  • other allergic events.

Rare side effects of Sodium Iodide I-131 include:

  • none 

Seek medical care or call 911 at once if you have the following serious side effects:

  • Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors;
  • Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
  • Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheartedness, or passing out.

This is not a complete list of side effects and other serious side effects or health problems that may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

What Other Drugs Interact with Sodium Iodide I-131?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist about all your products. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions or concerns.

What Are Warnings and Precautions for Sodium Iodide I-131?


  • Therapeutic and diagnostic use
  • Women who are pregnant or may become pregnant; defer use in women of childbearing age until the possibility of pregnancy has been ruled out
  • Breastfeeding
  • Therapeutic use
  • Vomiting and diarrhea
  • Treatment of thyroid malignancies shown to have no iodine uptake, which includes the majority of medullary and anaplastic carcinomas
  • Patients receiving concurrent anti-thyroid therapy

Effects of drug abuse


Short-Term Effects

See “What Are Side Effects Associated with Using Sodium Iodide I-131?”

Long-Term Effects

See “What Are Side Effects Associated with Using Sodium Iodide I-131?”


Diagnostic use

  • Recent intake of stable iodine in any form or the use of thyroid or anti-thyroid drugs will affect the uptake of radioIodide

Therapeutic use

  • Consider pre-treatment anti-thyroid medication to help deplete thyroid hormone; discontinue anti-thyroid therapy three days before administration of sodium Iodide I 131; consider a beta-blocker pre or post-treatment to minimize the risk of hyperthyroidism and thyroid storm
  • Instruct patients to follow radiation safety precautions after receiving therapy to minimize radiation contamination of other persons or the environment; patients should avoid close contact with others, especially pregnant women and children, and take care to avoid contamination of other persons or the environment with body fluids
  • Thyroiditis may cause gland enlargement resulting in tenderness and swelling of the neck, pain in swallowing, sore throat, and cough; which may occur approximately the third day after sodium Iodide I 131 administration. Consider management with pain-reliever or anti-inflammatory medications
  • Hypersensitivity reactions, including rash and hives, reported
  • Transplacental passage of sodium Iodide I-131 can cause severe and possibly irreversible hypothyroidism in neonates (see Contraindications)
  • Transient dose-related impairment of testicular function in men and transient ovarian insufficiency in women has been reported after sodium Iodide I 131 therapy; consider sperm banking for men who are anticipated to receive cumulative sodium Iodide I 131 doses greater than 19,000 MBq (520 mCi)
  • Therapy contributes to a patient’s overall long-term cumulative radiation exposure, which is associated with an increased risk of cancer; follow safe handling and administration to minimize radiation exposure to patients and healthcare providers

Radiation-induced toxicities

  • Dose-dependent fatalities (bone marrow suppression, malignancy)
  • Dose-dependent hematopoietic suppression which manifests as transient thrombocytopenia or neutropenia 3-5 weeks following sodium Iodide I 131 administrations, may lead to increased susceptibility to infections or bleeding
  • Salivary gland toxicity: sialadenitis, xerostomia
  • Lacrimal gland toxicity: conjunctivitis, xerophthalmia, and epiphora
  • Obtain complete blood count within one month of therapy; if patients show leukopenia or thrombocytopenia, use dosimetry to determine a safe sodium Iodide I 131 Activity, while delivering less than 2 Gy to bone marrow
  • Advise good hydration for one week following sodium Iodide I 131 administration and stimulate salivary flow via a sialagogue (.g. sugar-free candy or gum, pilocarpine, and ascorbic acid) to reduce radiation exposure to salivary glands
  • Advise patients to void frequently after administration of radioIodide to enhance excretion

Drug interaction overview

  • Concomitant use of bone marrow depressants may enhance depression of the hematopoietic system caused by the use of large doses of sodium Iodide I 131
  • Certain food or drugs may alter thyroid uptake of sodium Iodide I 131 and diminish effectiveness; recent intake of stable iodine in any form or the use of thyroid or anti-thyroid drugs may diminish thyroid uptake of sodium Iodide I 131
  • Review the patient’s history, current medications, and recent diagnostic tests before administration of sodium Iodide I 131
  • Advise patients to maintain a low-Iodide diet two weeks before radioIodide administration and continue for several days during the uptake or imaging process and to discontinue taking amiodarone, topical iodine, kelp, agar, carrageenan, Lugol solution, ethionamide medications (propylthiouracil, methimazole, carbimazole), multivitamins containing Iodide, natural or synthetic thyroid hormones, Iodide containing foods, iodized salt, dairy products, egg yolks, seafood, turkey and liver, before they undergo the procedure for the periods described in the prescribing information

Pregnancy & Lactation

  • Contraindicated in pregnancy because fetal exposure can lead to neonatal hypothyroidism, which in some cases is severe and irreversible
  • Data from published literature describe reports of neonatal thyroid abnormalities after fetal exposure; including agenesis of the thyroid and hypothyroidism; no animal reproductive studies have been conducted
  • A fetus exposed to sodium Iodide I 131 can develop neonatal hypothyroidism; delay in diagnosis of neonatal hypothyroidism after exposure to sodium Iodide I 131 in utero can result in severe sequelae such as cognitive impairment and delayed bone age; monitor thyroid function in any infant born after in utero exposure to sodium Iodide I 131
  • Pregnancy Testing
    • Obtain a pregnancy test in females of reproductive potential and verify the absence of pregnancy within 24 hours before administration of treatment
  • Contraception
    • Advise females and males of reproductive potential to use effective contraception during treatment and for at least six months after the last dose
  • Infertility
    • Females: Fertility may be impaired with treatment; transient amenorrhea and ovarian insufficiency observed after sodium Iodide I 131; therapy in females; the literature describes reports of transient menstrual cycle irregularities, including amenorrhea, and ovarian failure in females treated with cumulative doses of 1,000 MBq to 59,000 MBq (27 mCi to 1,595 mCi) sodium Iodide I 131; in a published literature analysis, the effects on fertility occurred in up to 30% of women treated with sodium Iodide I 131, and may resolve 12 months after treatment.
    • Males: Fertility may be impaired with treatment; discuss sperm banking for males who are expected to receive a high cumulative dose of sodium Iodide I 131; transient dose-related impairment of testicular function after sodium Iodide I 131 therapy has been reported in the published literature; the literature describes reports of males treated with sodium Iodide I 131 at doses of 370 MBq to 22,000 MBq (10 mCi to 595 mCi) resulting in transiently impaired testicular function (including spermatogenesis); the risk of persistent testicular dysfunction increases after administration of repeated or high cumulative radioIodide exposure
  • Lactation
    • Contraindicated in lactating women because sodium Iodide I 131 concentrates in the breast via increased expression of sodium Iodide symporter in breast tissue with lactation and can lead to hypothyroidism in the infant through breastfeeding
    • Advise lactating women to discontinue breastfeeding at least 6 weeks before administration of sodium Iodide I 131 to allow sufficient time for involution to occur and to avoid excessive concentration of sodium Iodide I 131 in breast tissue
    • Consider administration of drugs to suppress lactation; consider diagnostic scintigraphy before administration of sodium Iodide I 131 to assess the persistence of uptake by breast tissue; if sodium Iodide I 131 is administered in the postpartum period, the lactating mother should not breastfeed the infant
    • If sodium Iodide I 131 is administered postpartum, breastfeeding should not be restarted for the remainder of the postpartum period
    • Infants exposed to sodium Iodide I 131 through breast milk are at risk for the development of hypothyroidism because sodium Iodide I 131 is distributed into breast milk and may reach concentrations equal to or greater than concentrations in maternal plasma

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