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Sodium Iodide I131

Pronunciation

(SOW dee um EYE oh dide eye one THUR tee one)

Index Terms

  • I 131
  • Iodide 131
  • Iodine 131

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Capsule [diagnostic]: 0.555 megabecquerels [15 microcuries]; 0.925 megabecquerels [25 microcuries]; 1.85 megabecquerels [50 microcuries]; 3.7 megabecquerels [100 microcuries]

Capsule [therapeutic]: 28-3700 megabecquerels [0.75-100 millicuries]

Iodotope®: 37-4810 megabecquerels [1-130 millicuries]

Kit [therapeutic]:

Hicon™ 9.25 gigabecquerels (250 millicuries):

Capsule: Dibasic sodium phosphate 300 mg (10s)

Capsule: Empty large gelatin capsule (10s)

Solution: Sodium iodide I131 9.25 gigabecquerels (250 millicuries) per 0.25 mL (0.25 mL) [contains edetate disodium, sodium thiosulphate and dibasic sodium phosphate]

Hicon™ 18.5 gigabecquerels (250 millicuries):

Capsule: Dibasic sodium phosphate 300 mg (10s)

Capsule: Empty large gelatin capsule (10s)

Solution: Sodium iodide I131 18.5 gigabecquerels (500 millicuries) per 0.5 mL (0.5 mL) [contains edetate disodium, sodium thiosulphate and dibasic sodium phosphate]

Hicon™ 37 gigabecquerels (1000 millicuries):

Capsule: Dibasic sodium phosphate 300 mg (10s)

Capsule: Empty large gelatin capsule (10s)

Solution: Sodium iodide I131 37 gigabecquerels (1000 millicuries) per 1 mL (1 mL) [contains edetate disodium, sodium thiosulphate and dibasic sodium phosphate]

Solution [therapeutic]: 129.5-5550 megabecquerels per vial [3.5-150 millicuries per vial; contains sodium bisulfite and edetate disodium]

Brand Names: U.S.

  • Hicon

Pharmacologic Category

  • Antithyroid Agent
  • Radiopharmaceutical

Pharmacology

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.

Absorption

Oral: Rapidly (90% within 60 minutes)

Distribution

Extracellular fluid; primarily trapped by the thyroid

Metabolism

Iodide is rapidly oxidized to iodine in the thyroid

Excretion

Urine (37% to 75%); feces ~10%

Protein Binding

None

Use: Labeled Indications

Diagnostic agent: Diagnostic use in performance of radioactive iodide (RAI) uptake test to evaluate thyroid function; diagnostic doses may also be used to localize metastases associated with thyroid malignancies.

Therapeutic agent: Treatment of hyperthyroidism and 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.

Contraindications

Preexisting vomiting and diarrhea (treatment); concurrent antithyroid medication (discontinue 3 to 4 days prior to administration); women who are or may become pregnant; breast-feeding; treatment of thyroid malignancies shown to have no iodide uptake, which include the majority of medullary and anaplastic carcinomas.

Dosing: Adult

Note: If dose or dose within range exceeds 1000 microcuries, dose will be expressed as millicuries. Adhere to radiation safety precautions regarding radioactive iodine treatment.

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: 5-15 microcuries (or 0.185–0.555 megabecquerels)

Scintiscanning: 50-100 microcuries (or 1.85-3.7 megabecquerels)

Localization of extrathyroid metastases: 1000 microcuries (or 37 megabecquerels)

Treatment: Oral:

Hyperthyroidism: 4-10 millicuries (or 148-370 megabecquerels)

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 on % of dose])/1000

Graves’ disease (off-label dosing): 10-15 millicuries (or 370-555 megabecquerels) or 150 microcuries/g of tissue corrected for 24-hour radioactive iodine uptake (see dose equation) (Bahn, 2011)

Toxic multinodular goiter (off-label dosing): 150-200 microcuries/g of tissue corrected for 24-hour radioactive iodine uptake (see dose equation); if hyperthyroidism persists, may repeat after 6 months if needed (Bahn, 2011)

Toxic thyroid adenoma (off-label dosing): 10-20 millicuries (or 370-740 megabecquerels) or 150-200 microcuries/g of tissue corrected for 24-hour radioactive iodine uptake (see dose equation); if hyperthyroidism persists, may repeat after 6 months if needed (Bahn, 2011; Zakavi, 2009)

Thyroid cancer: 100 to 150 millicuries (or 3700 to 5550 megabecquerels); Postoperative ablation of residual tissue: Usual dose: 50 millicuries (or 1850 megabecquerels)

Hicon: Ablation of normal thyroid tissue: Initial: 30-100 millicuries (or 1100-3700 megabecquerels)

Subsequent metastases ablation: 100-200 millicuries (or 3700-7400 megabecquerels)

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Note: If dose or dose within range exceeds 1000 microcuries, dose will be expressed as millicuries. Adhere to radiation safety precautions regarding radioactive iodine treatment.

Graves’ disease (off-label use): Children ≥5 years: Oral: Dose is dependent upon gland size; >150 microcuries/g of thyroid tissue is necessary to induce hypothyroidism; if gland is between 50-80 g, higher activities (200-300 microcuries/g of thyroid tissue) may be needed. Note: Therapy in children between 5-10 years of age is acceptable if the calculated dose is <10 millicuries (Bahn, 2011)

Dosing: Renal Impairment

There are no dosage adjustments provided in manufacturer’s labeling. However, patients with renal impairment may have decreased clearance and increased radiation exposure. Sodium iodide I131 is dialyzable.

Dosing: Hepatic Impairment

There are no dosage adjustments provided in manufacturer’s labeling.

Reconstitution

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, transfer appropriate amount to shielded empty vial. Dilute with purified water containing sodium thiosulfate 0.2% (as reducing agent). 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.

Administration

Ensure adequate hydration before and after treatment. Adhere to radiation safety precautions regarding radioactive iodine treatment.

Hicon must be diluted prior to administration.

Radiopharmaceutical; use appropriate precautions for handling and disposal. Waterproof gloves should be worn while handling and administering sodium iodide I131.

Dietary Considerations

Some dietary sources of iodine include cow's milk and dairy products, fish, seaweed, eggs, chocolate, and iodized salt.

Storage

Store at controlled room temperature of 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.

Drug Interactions

Amiodarone: May diminish the therapeutic effect of Sodium Iodide I131. Consider therapy modification

Antithyroid Agents: May diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue antithyroid therapy 3-4 days prior to sodium iodide I-131 administration. Avoid combination

Thyroid Products: May diminish the therapeutic effect of Sodium Iodide I131. Avoid combination

Adverse Reactions

Frequency not defined, dose dependent.

Cardiovascular: Chest pain, tachycardia

Central nervous system: Cerebral edema (in patients with iodine-avid brain metastases), metallic taste

Dermatologic: Alopecia, pruritus, skin lesion (iododerma), skin rash, urticaria

Endocrine & metabolic: Hyperthyroidism, hypoparathyroidism, hypothyroidism, thyroiditis, thyroid storm

Gastrointestinal: Gastritis, nausea (high dose used in treatment of thyroid cancer), odynophagia, salivary gland disease, sialadenitis, sore throat, unpleasant taste, vomiting

Genitourinary: Infertility (transient; may be permanent in males with repeated or high dose)

Hematologic & oncologic: Acute leukemia, anemia, bone marrow depression (high dose used in treatment of thyroid cancer), hematologic abnormality, leukopenia, solid tumor, thrombocytopenia

Hypersensitivity: Anaphylaxis, hypersensitivity reaction

Immunologic: Immunosuppression

Neuromuscular & skeletal: Neck discomfort (tenderness/swelling)

Ophthalmic: Lacrimation

Respiratory: Bronchospasm, cough, pulmonary fibrosis (in patients with iodine-avid lung metastases), radiation pneumonitis (in patients with iodine-avid lung metastases)

Miscellaneous: Chromosomal abnormality, local swelling, radiation injury

Postmarketing and/or case reports (Limited to important or life-threatening): Neoplasm (rare; causative role not established)

Warnings/Precautions

Concerns related to adverse effects:

• Hypersensitivity: Hypersensitivity reactions (including rash and hives) have been reported following sodium iodide I131 administration. Sodium iodide I131 solution contains 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.

• Infertility: Transient, dose-related testicular function impairment after sodium iodide I131 use; consider sperm banking for men who are anticipated to receive a high cumulative dose (eg, >14 GBq). Transient ovarian failure has been observed in females after sodium iodide I131 treatment.

• 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.

• 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. 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.

Disease-related concerns:

• 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.

Special populations:

• 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.

• Patients <30 years of age: Use is not generally recommended for treatment of hyperthyroidism in patients <30 years of age.

• 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.

Special handling:

• Radiopharmaceutical: Use appropriate precautions for handling, disposal, and minimizing exposure to patients and healthcare 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.

Other warnings/precautions:

• Appropriate use: Patients should be adequately hydrated prior to dosing.

Monitoring Parameters

Evaluate renal function prior to treatment.

Pregnancy Risk Factor

X

Pregnancy Considerations

Iodine-131 crosses the placenta and may cause severe and irreversible hypothyroidism in neonates. Pregnancy should be ruled out prior to therapy; use is contraindicated in pregnancy. Use of 2 effective methods of contraception is recommended (for females and males) during treatment and for at least 12 months following administration; if additional iodide I131 therapy or radionuclide imaging is anticipated, the use of 2 effective methods of contraception may be necessary for at least 1 year. Elective diagnostic procedures should be delayed until after delivery (Parker, 2004).

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience nausea or vomiting. Have patient report immediately to prescriber angina, tachycardia, dizziness, shortness of breath, difficulty swallowing, painful swallowing, chills, pharyngitis, severe loss of strength and energy, dry eyes, dry mouth, persistent cough, neck tenderness, or neck edema (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

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