Sodium Iodide I131
Medically reviewed by Drugs.com. Last updated on Aug 23, 2020.
(SOW dee um EYE oh dide eye one THUR tee one)
- I 131
- Iodide 131
- Iodine 131
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Generic: 100 mCi (5s)
Hicon: 250 mCi, 500 mCi, 1000 mCi (1 mL) [contains edetate (edta) disodium dihydrate]
Brand Names: U.S.
- Antithyroid Agent
- Diagnostic Agent
Oral sodium iodide I131 is rapidly absorbed and distributed within the extracellular fluid of the body. Iodide is concentrated in the thyroid via the sodium/iodide symporter, and subsequently oxidized to iodine. Beta emission of sodium iodide I131 destroys thyroid tissue.
Oral: Rapidly (90% within 60 minutes)
Extracellular space; primarily trapped by the thyroid
Iodide is rapidly oxidized to iodine in the thyroid
Urine (37% to 75%); feces ~10%
Use: Labeled Indications
Diagnostic agent: Diagnostic use in performance of radioactive iodide (RAI) uptake test to evaluate thyroid function and for thyroid imaging. Note: Other agents (eg, sodium iodide I123, technetium-99m pertechnetate) are preferred for routine thyroid scintigraphy for benign disease due to increased thyroid radiation exposure with sodium iodide I131 (ACR/SNMMI/SPR 2019).
Therapeutic agent: Treatment of hyperthyroidism and select cases of thyroid carcinomas (if the lesions take up iodide); palliative effects may be observed in patients with advanced thyroid malignancy if the metastatic lesions take up iodide.
Off Label Uses
Whole body imaging for thyroid cancer metastases
According to the American College of Radiology, Society of Nuclear Medicine and Molecular Imaging, and Society for Pediatric Radiology practice parameter for the performance of scintigraphy and uptake measurements for benign and malignant thyroid disease, sodium iodide I131 is recommended for diagnostic whole-body imaging for thyroid cancer [ACR/SNMMI/SPR 2019].
Preexisting vomiting and diarrhea (treatment); concurrent antithyroid medication (discontinue 3 to 4 days prior to administration); women who are or may become pregnant; breastfeeding; treatment of thyroid malignancies shown to have no iodide uptake, which include the majority of medullary and anaplastic carcinomas
Note: If dose or dose within range exceeds 1,000 microcuries, dose will be expressed as millicuries. Adhere to radiation safety precautions regarding radioactive iodine treatment. Discontinue antithyroid medications 3 to 4 days prior to administration of sodium iodide I131.
Diagnostic procedures: Oral (based on a 70 kg patient): Note: Consult manufacturer potency tables when applicable. All doses should be individualized; general ranges are listed here:
Thyroid uptake: 5 to 10 microcuries (or 0.185 to 0.37 megabecquerels) 24 hours prior to uptake measurement (ACR/SNMMI/SPR 2019; manufacturer's labeling); maximum: 10 microcuries (0.37 megabecquerels) (ACR/SNMMI/SPR 2019).
Dosage adjustment if used in conjunction with technetium Tc 99m sodium pertechnetate: 4 to 5 microcuries (0.15 to 0.185 megabecquerels) (ACR/SNMMI/SPR 2019).
Thyroid imaging: 50 to 100 microcuries (or 1.85 to 3.7 megabecquerels) 16 to 24 hours prior to imaging. Note: Other agents (eg, sodium iodide I123, technetium-99m pertechnetate) are preferred for routine thyroid scintigraphy for benign disease due to increased thyroid radiation exposure with sodium iodide I131 (ACR/SNMMI/SPR 2019).
Whole-body imaging for thyroid cancer metastases (off label): 1 to 5 millicuries (37 to 185 megabecquerels) 24 to 72 hours prior to imaging (ACR/SNMMI/SPR 2019).
Treatment: Individual dose based on thyroid uptake and gland size. Oral:
Hyperthyroidism: Manufacturer's labeling recommends 4 to 10 millicuries (or 148 to 370 megabecquerels); however, due to high failure rates, RAI therapy with low activities is generally not recommended (ATA [Ross 2016]).
Graves disease (off-label dosing): 10 to 15 millicuries (or 370 to 555 megabecquerels) or 150 microcuries/g of tissue corrected for 24-hour radioactive iodine uptake (see dose equation below) (ATA [Ross 2016]).
Note: Radioactive iodine (RAI) therapy is not recommended in patients with active and moderate to severe or sight-threatening Graves orbitopathy. RAI therapy may be considered in patients with active and mild disease; however, if risk factors for worsening of orbitopathy are present (eg, smoking, high thyrotropin receptor antibodies), concomitant use of glucocorticoids is strongly recommended. In the absence of risk factors, concomitant glucocorticoid use may still be considered (ATA [Ross 2016]).
Toxic multinodular goiter (off-label dosing): 150 to 200 microcuries/g of tissue corrected for 24-hour radioactive iodine uptake (see dose equation below); if hyperthyroidism persists, may repeat after 6 months if needed (ATA [Ross 2016]).
Toxic thyroid adenoma (off-label dosing): 10 to 20 millicuries (or 370 to 740 megabecquerels) or 150 to 200 microcuries/g of tissue corrected for 24-hour radioactive iodine uptake (see dose equation below); if hyperthyroidism persists, may repeat after 6 months if needed (ATA [Ross 2016]).
Dose equation corrected for 24-hour radioactive iodine uptake: Activity (millicuries) = (gland weight in grams x desired dose in microcuries/gram x [1/24 hour uptake in % of dose])/1,000 (ATA [Ross 2016]).
Ablation of normal thyroid tissue: Initial: 30 to 100 millicuries (or 1,100 to 3,700 megabecquerels). Note: If remnant ablation is performed after total thyroidectomy for American Thyroid Association (ATA) low-risk thyroid cancer or intermediate-risk disease with lower risk features, a low administered activity of ~30 millicuries is generally favored over higher administered activities. For initial adjuvant therapy when microscopic residual disease is suspected (in the absence of known distant metastases), up to 150 millicuries has been recommended (ATA [Haugen 2015]).
Subsequent metastases ablation: 100 to 200 millicuries (or 3,700 to 7,400 megabecquerels).
Refer to adult dosing.
Empiric dosing for subsequent pulmonary micrometastases ablation for patients ≥70 years: 100 to 150 millicuries (ATA [Haugen 2015])
Graves disease (off-label use): Children ≥5 years of age: Oral: Dose is dependent upon gland size; >150 microcuries/g of thyroid tissue is necessary to induce hypothyroidism; if gland is between 50 to 80 g, higher activities (200 to 300 microcuries/g of thyroid tissue) may be needed. Therapy in children between 5 to 10 years of age is acceptable if the calculated dose is <10 millicuries (ATA [Ross 2016])
Radiopharmaceutical; use appropriate precautions for handling and disposal. Wear waterproof gloves for preparation, handling, and administration. Maintain adequate shielding during the radiation-emitting life. Measure the appropriate dose using a suitable radioactivity calibration system immediately prior to administration.
Hicon: Using a shielded syringe, withdraw the required volume and transfer appropriate amount to shielded empty vial. Dilute with purified water containing sodium thiosulfate 0.2% (as reducing agent). For solution, provide dose in shielded container. For capsules, place unopened small capsule (contains dibasic sodium phosphate as absorbing buffer) into bottom half of opened large (empty) capsule; inject appropriate volume of diluted sodium iodide I131 into the center of the unopened small capsule, cover and seal with upper half of large capsule. Refer to manufacturer's labeling for additional details.
Ensure adequate hydration before and after treatment; instruct patients to void frequently to enhance elimination of radioiodide not absorbed by thyroid. Adhere to radiation safety precautions regarding radioactive iodine treatment.
Hicon: Administer on an empty stomach; patient should fast at least 2 hours before and 2 hours after administration to ensure adequate absorption. Solution must be diluted and prepared prior to administration; do not administer concentrated solution. Provide solution dose in a shielded container with a straw for administration.
Radiopharmaceutical; use appropriate precautions for handling and disposal. Waterproof gloves should be worn while handling and administering sodium iodide I131.
The manufacturer recommends maintaining a low iodide diet two weeks before administration and to continue for several days during the uptake and imaging process.
In the treatment of Graves disease, it has been recommended that a special diet prior to RAI therapy is not required, but nutritional supplements containing excess iodine and seaweeds be avoided for at least 7 days; a low-iodine diet may benefit those with relatively low RAI uptake to increase the proportion of RAI trapped (ATA [Ross 2016])
Some dietary sources of iodine include cow's milk and dairy products, fish, seaweed, eggs, chocolate, and iodized salt.
Diagnostic: Store at 15°C to 30°C (59°F to 86°F). Products should be adequately shielded. Measure dose immediately prior to administration.
Therapeutic: Store at 20°C to 25°C (68°F to 77°F). Products should be adequately shielded. Measure dose immediately prior to administration.
Hicon: Prior to use, store solution at 2°C to 25°C (36°F to 77°F). Prepared capsule should be stored in suitable polypropylene container inside a lead pot; use within 7 days of preparation.
Amiodarone: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue amiodarone at least 6 months before sodium iodide I-131 administration, and avoid concurrent use. Avoid combination
Antithyroid Agents: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue antithyroid medications at least 3 days before sodium iodide I-131 administration, and avoid concurrent use. Exceptions: Potassium Iodate; Potassium Iodide. Avoid combination
Iodinated Contrast Agents: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue iodinated contrast agents before sodium iodide I-131 administration, and avoid concurrent use. Stop water soluble agents 2 months before, and stop lipophilic agents 6 months before, sodium iodide I-131 administration. Avoid combination
Iodine: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue topical iodine at least 3 weeks before sodium iodide I-131 administration, and avoid concurrent use. Avoid combination
Potassium Iodate: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue potassium iodate at least 3 weeks before sodium iodide I-131 administration, and avoid concurrent use. Avoid combination
Potassium Iodide: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue potassium iodide at least 3 weeks before sodium iodide I-131 administration, and avoid concurrent use. Avoid combination
Povidone-Iodine (Topical): May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue topical povidone-iodine at least 3 weeks before sodium iodide I-131 administration, and avoid concurrent use. Avoid combination
Sodium Iodide: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue sodium iodide supplementation at least 10 days before sodium iodide I-131 administration, and avoid concurrent use. Avoid combination
Thyroid Products: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue thyroid products before sodium iodide I-131 administration, and avoid concurrent use. Stop triiodothyronine (T3) 2 weeks before, and stop thyroxine (T4) 4 weeks before, sodium iodide I-131 administration. Avoid combination
Frequency not defined
Cardiovascular: Chest pain, tachycardia
Central nervous system: Cerebral edema (in patients with iodine-avid brain metastases), headache
Dermatologic: Pruritus, skin lesion (iododerma), skin rash, urticaria
Endocrine & metabolic: Goiter, hyperthyroidism, hypoparathyroidism, hypothyroidism, ovarian failure (transient), thyroid storm
Gastrointestinal: Gastritis, nausea, salivary gland disease, sialadenitis, sore throat, vomiting, xerostomia
Genitourinary: Inhibition of testicular function (transient)
Hematologic & oncologic: Anemia, bone marrow depression, hematologic abnormality, leukemia, leukopenia, neoplasm, solid tumor, thrombocytopenia
Hepatic: Hepatic insufficiency
Hypersensitivity: Hypersensitivity reaction
Local: Local pain (pain on swallowing), local swelling (thyroid or site of iodide avid tumor), localized tenderness
Ophthalmic: Conjunctivitis, epiphora, lacrimal duct obstruction (dacryostenosis), lacrimal dysfunction, xerophthalmia
Respiratory: Bronchospasm, cough, pulmonary fibrosis (in patients with iodine-avid lung metastases), radiation pneumonitis (in patients with iodine-avid lung metastases)
Miscellaneous: Radiation injury (including radiation sickness)
Concerns related to adverse effects:
• Hypersensitivity: Hypersensitivity reactions (including rash and hives) have been reported following sodium iodide I131 administration. Sodium iodide I131 solution may contain sodium bisulfite, a sulfite that may cause allergic-type reactions, including anaphylactic symptoms and life-threatening or less severe asthmatic episodes. The overall incidence of sulfite sensitivity in the general population is unknown and probably low. Sulfite sensitivity is seen more frequently in asthmatic than in nonasthmatic people. During pretherapy assessment, question patients about a history of hypersensitivity to sulfite.
• Radiation-induced thyroiditis: Sodium iodide I131 may cause thyroiditis (with gland enlargement) and thyroid hormone release, particularly if used in the treatment of hyperthyroidism. Thyroiditis may cause or worsen hyperthyroidism and may lead to thyroid storm. When treating hyperthyroidism, consider pretreatment with antithyroid medication to help deplete thyroid hormone content within the gland. Discontinue antithyroid medication at least 3 days prior to sodium iodide I131 administration. Consider beta-blocker therapy prior to sodium iodide I131 administration to minimize the risk of hyperthyroidism and thyroid storm. Thyroiditis may result in gland enlargement with neck tenderness and swelling, pain with swallowing, sore throat, and cough; may require management with anti-inflammatory medications or analgesics.
• Radiation toxicities: Radiation-induced toxicities, including dose-dependent fatalities, have been reported following sodium iodide I131 therapy. Postmarketing reports have identified an increased risk for neoplasia, as well as a risk of hematopoietic suppression (transient neutropenia/thrombocytopenia; onset 3 to 5 weeks). Salivary and lacrimal gland toxicity is relatively common and may manifest as conjunctivitis, xerophthalmia, epiphora, sialadenitis, and xerostomia.
• Thyroid-stimulating hormone/thyroid enlargement: Enhanced thyroid-stimulating hormone (TSH) secretion (eg, following discontinuation of antithyroid medications, or the administration of TSH to enhance sodium iodide I131 uptake) may cause thyroid enlargement and obstructive complications of the trachea, esophagus, or blood vessels in the neck. Evaluate patients at high risk of obstructive complications prior to preparative treatments known to cause thyroid enlargement.
• Graves orbitopathy: Radioactive iodine therapy is not recommended in patients with active and moderate to severe or sight-threatening Graves orbitopathy. Radioiodine therapy may be considered in patients with active and mild disease; however, if patients have additional risk factors for worsening orbitopathy (eg, high thyrotropin receptor antibodies, smoking) concomitant glucocorticoid therapy is strongly recommended. In the absence of risk factors for worsening orbitopathy in patients with mild disease, glucocorticoid coverage may still be considered (ATA [Ross 2016]).
• Hyperthyroidism/thyrotoxic cardiac disease: May be aggravated by radiation thyroiditis; consider pre- and post-treatment with antithyroid agents and/or beta-blockers.
• Hypochloremia: May increase thyroid uptake of sodium iodide I131.
• Renal impairment: Sodium iodide I131 is eliminated predominantly renally; patients with renal impairment may have decreased clearance and increased radiation exposure. Sodium iodide I131 is dialyzable and hemodialysis may be used to decrease total body radiation exposure. Evaluate renal function prior to treatment. Nephrosis may increase thyroid uptake of sodium iodide I131.
Concurrent drug therapy issues:
• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.
• Iodine/thyroid medications: Concomitant use of iodine, thyroid, or antithyroid medications may interfere with the uptake of radioiodide; medications should be discontinued for an appropriate time prior to dosing.
• Elderly: Elderly patients are more likely to have decreased renal function and comorbid conditions; may require close evaluation, dose selection, and follow-up compared with younger patients. When treating hyperthyroidism in geriatric patients at risk of developing cardiac complications, pre- and post-treatment with antithyroid drugs and/or beta-blockers may minimize the risk of excessive post-treatment hyperthyroidism due to radiation-induced thyroiditis.
• Pediatric: The thyroid gland may be more sensitive to the effects of sodium iodide I131 in pediatric patients; safety and efficacy have not been established.
• Radiopharmaceutical: Use appropriate precautions for handling, disposal, and minimizing exposure to patients and health care personnel. Use only under supervision of individuals with experience/training in the handling of radioactive materials approved by the applicable regulatory authority. Unwanted radiation exposure can occur from handling and administration of radiopharmaceuticals or from contaminated waste products, including urine and feces. Patients must be instructed in measures to minimize exposure of others.
• Appropriate use: Patients should be adequately hydrated prior to and for at least 1 week following administration. Frequent voiding is recommended to enhance radioiodide excretion. Stimulate salivary flow (gum or sugar-free candy) to reduce radiation exposure to salivary glands. Avoid close contact with others (especially pregnant women and children) and contamination of other persons or the environment with body fluids.
Thyroid function tests (TSH, free T4, total T3) within 1 to 2 months post-treatment and at 4 to 6 week intervals for 6 months, or until hypothyroid and stable on thyroid hormone replacement (Graves disease, toxic multinodular goiter, toxic adenoma) (ATA [Ross 2016]).
Evaluate pregnancy status prior to use; a negative human chorionic gonadotropin (hCG) pregnancy test should be done within 24 hours prior to administration in females of reproductive potential (ACR/ACNM/ASTRO/SNMMI/SPR 2019).
Evaluate pregnancy status prior to use; a pregnancy test should be done prior to administration in females of reproductive potential. Pregnancy should be ruled out prior to therapy.
Effective contraception is recommended by the manufacturer for females and males during treatment for thyroid disease and for at least 6 months following administration. Practice guidelines advise against planning a pregnancy for 6 to 12 months following use as a diagnostic or therapeutic agent (ACR/ACNM/ASTRO/SNMMI/SPR 2019; IAEA 2018).
Transient infertility may occur in males and females (dose related). Transient amenorrhea and ovarian insufficiency have been reported in females. Transient testicular function impairment has been observed in males; consider sperm banking in males prior to therapeutic use.
Sodium iodide I131 crosses the placenta.
Fetal exposure to sodium iodide I131 may cause severe and irreversible hypothyroidism in neonates. A delayed diagnosis following in utero exposure may lead to decreased mental capacity and delayed skeletal maturation. Monitor thyroid function of infants born following inadvertent in utero exposure.
Use as either a diagnostic or therapeutic agent is contraindicated in pregnancy.
Health care providers who are pregnant should avoid direct patient care, and pregnant females should also limit close contact with patients undergoing treatment with sodium iodide I131 for thyroid disease (ACR/ACNM/ASTRO/SNMMI/SPR 2019).
What is this drug used for?
• It is used to treat an overactive thyroid gland.
• It is used to treat thyroid cancer.
• It is used to test for thyroid problems.
• It may be given to you for other reasons. Talk with the doctor.
All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:
WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:
• Thyroid problems like change in weight without trying, anxiety, agitation, feeling very weak, hair thinning, depression, neck swelling, trouble focusing, inability handling heat or cold, menstrual changes, tremors, or sweating
• Chest pain
• Fast heartbeat
• Shortness of breath
• Painful swallowing
• Sore throat
• Severe loss of strength and energy
• Dry eyes
• Dry mouth
• Mouth pain
• Persistent cough
• Neck tenderness
• Neck swelling
• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.
Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a limited summary of general information about the medicine's uses from the patient education leaflet and is not intended to be comprehensive. This limited summary does NOT include all information available about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not intended to provide medical advice, diagnosis or treatment and does not replace information you receive from the healthcare provider. For a more detailed summary of information about the risks and benefits of using this medicine, please speak with your healthcare provider and review the entire patient education leaflet.
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More about sodium iodide-i-131
- Side Effects
- During Pregnancy or Breastfeeding
- Dosage Information
- Drug Interactions
- Drug class: antithyroid agents