Sodium iodide I-131 uses, doses, brand name and effects

Description of Sodium iodide I-131

Sodium iodide I-131 (Na¹³¹I), is an oral radioactive iodide isotope that is used both therapeutically and diagnostically. The radiopharmaceutical is selectively trapped by non-malignant and, to a lesser degree, malignant thyroid tissue. Sodium iodide I-131 was approved in 1957 for radioactive iodide ablation in the treatment of hyperthyroidism and select cases of thyroid carcinoma. Radioiodide is not taken up by the majority of medullary and anaplastic carcinomas including giant cell and spindle cell carcinoma of the thyroid or amyloid solid carcinomas. When used therapeutically, the preferred formulation and dosing regimen is highly physician specific. Sodium iodide I-131 was also approved as a diagnostic aid in December 2005; the gamma and beta particle emissions are used to evaluate thyroid function via the radioactive iodine (RAI) uptake test and for thyroid imaging.

Mechanism of Action of Sodium iodide I-131

Sodium iodide I-131 is a radiopharmaceutical. The radioactive isotope decays by beta and gamma emission. Sodium iodide I-131 mimics nonradioactive iodine exactly, and is rapidly trapped by thyroid tissue after administration. The extent of iodide uptake into the thyroid is estimated to be 10—35% at 24 hours post oral administration; however, the extent of uptake is altered by the function of the thyroid gland and the pretreatment iodine status of the patient.

When used as a diagnostic agent, the administration of radioactive iodine can be used to determine iodide uptake as a measure of thyroid function. Sodium iodide I-131 emits gamma radiation that can be detected by a gamma probe several hours after oral administration. By comparing the amount of sodium iodide I-131 that is taken up by the thyroid to the standard uptake in euthyroid patients, the patient’s thyroid function can be determined. Similarly, sodium iodide I-131 is taken up by metastatic thyroid carcinoma lesions that can be detected by whole body iodine scans. Beta-1, Beta-3, Beta-4, Gamma-7, Gamma-14, and Gamma-17 photons are useful for detection and imaging.

When used as a therapeutic agent, at doses required for ablation of thyroid tissue, approximately 90 percent of the local irradiation is caused by beta emissions and 10 percent is caused by gamma emissions. The radiation disrupts chemical bonds within the surrounding cells resulting in DNA molecule damage, subsequent cellular damage, and cell death. Unintended adverse events result both from radionucleotide concentration by other tissues (i.e., the salivary glands, oral mucosa, gastrointestinal mucosa) and radionucleotide excretion by the kidneys.

Pharmacokinetics :  Sodium iodide I-131 is administered orally. After absorption, sodium iodide I-131 is distributed within the extracellular space, where it is then taken up by the thyroid or excreted renally. The sodium-iodide symporter (NIS) is responsible for the concentration of iodide in the thyroid. Under normal circumstances, this active transport process concentrates iodide 20 to 40 times the plasma concentration. Thyroid uptake is increased in hyperthyroidism (up to 10-fold) and decreased in hypothyroidism. In the thyroid, trapped iodide is oxidized to iodine and organified. NIS also mediates iodide transport to other tissues including the salivary glands, nasolacrimal duct, lacrimal sac, stomach, choroid plexus, breasts, liver, gall bladder, and kidneys. The normal range of urinary excretion is 37% to 75% of the administered dose, varying with the thyroid and renal function of the patient; fecal excretion is approximately 10% and sweat excretion is negligible. Sodium iodide I-131 decays by beta emission and associated gamma emission, with a physical half-life of 8.04 days.

Route-Specific Pharmacokinetics
Oral Route
Sodium iodide I-131 is readily absorbed from the upper gastrointestinal tract (90% in 60 minutes).

Special Populations
Renal Impairment
Sodium iodide I-131 is substantially excreted by the kidney. The pharmacokinetics of sodium iodide I-131 in 2 patients with thyroid cancer and end stage renal disease undergoing continuous ambulatory peritoneal dialysis (CAPD) were compared to 8 euthyroid CAPD patients and 8 thyroid cancer patients with normal renal function. In patients undergoing CAPD, serum radioiodine half-times were 5 times longer than half-times in patients with normal renal function. Similarly, clearance rates in the CAPD patients were 20% of the clearance rates in patients with normal renal function. Subsequently, sodium iodide I-131 was administered to the 2 CAPD patients with thyroid cancer at 20 percent of standard dosage with resultant equivalent exposure to total body and red marrow. In addition, sodium iodide I-131 is readily dialyzable; in 2 chronic hemodialysis patients with thyroid carcinoma that received ablation thyroid therapy, sodium iodide I-131 was effectively removed 20 to 24 hours after I-131 administration during a standard 3 or 4 hour hemodialysis session. In both cases, after 1 session, radiation levels were less than 5 mR/hour allowing patients to be discharged to home.

Other
Thyroid Impairment
Thyroid uptake of iodide is usually increased in patients with hyperthyroidism and goiter with impaired hormone synthesis, decreased in patients with hypothyroidism, and normal to decreased in patients with hypothyroidism who are receiving iodine.

• Sodium Iodide I 131

• Iodotope

• Diagnostic Agent, Radiopharmaceutical Imaging
• Diagnostic Agent, Thyroid Function

• Hyperthyroidism: Adult
• Radionuclide thyroid imaging, for evaluation of thyroid function: Adult
• Thyroid cancer: Adult
• Thyroid cancer, metastases localization; Diagnosis: Adult

• Cardiovascular: Chest pain, Tachycardia
• Dermatologic: Hives, Pruritus, Rash
• Gastrointestinal: Disorder of salivary gland, Nausea, Vomiting
• Ophthalmic: Disorder of lacrimal gland

• Endocrine metabolic: Thyroid storm
• Hematologic: Acute leukemia, Bone marrow depression, Disorder of hematopoietic structure, Leukopenia
• Immunologic: Hypersensitivity reaction

• Use proper procedures for handling and disposal of radiopharmaceuticals
• Do not use after expiration date on product label
• Do not use if solution is cloudy, discolored, or contains particulate matter
• Use care to minimize radiation exposure to patient and occupational worker
• Wear waterproof gloves during the entire handling and administration
• Maintain adequate shielding during the life of the product
• Measure patient dose with a suitable radioactivity calibration system immediately prior to administration
• Oral: (HICON(R) capsule and solution) Using the calibration date and radionuclidic concentration, calculate the required volume of solution to produce the necessary dose in megabecquerels or milliCuries .
• Oral: (HICON(R) solution) Do not directly administer to patients; solution must be diluted and prepared
• Oral: (HICON(R) solution) Remove the required volume with a shielded syringe and transfer to a shielded receiving vial
• Oral: (HICON(R) solution) Add diluent to the receiving vial to produce a final dose of the desired volume; recommended diluent is Purified Water USP containing 0.2% Sodium Thiosulfate USP as a reducing agent; do not use acidic diluents
• Oral: (HICON(R) solution) Present the dose in a shielded container for administration to the patient with a straw .
• Oral: (HICON(R) capsule) Open 1 large capsule (empty capsule) by pulling apart the capsule in two pieces
• Oral: (HICON(R) capsule) Insert an unopened small capsule (300 mg of Dibasic Sodium Phosphate Anhydrous USP as absorbing buffer) into the bottom half of the empty large capsule
• Oral: (HICON(R) capsule) Withdraw the the required volume of solution from the vial with an appropriate syringe and inject into the center of the small capsule through the top. Wait 30 seconds for the solution to be absorbed by the absorbing buffer .
• Oral: (HICON(R) capsule) Slip the upper half of the large capsule over the bottom half to cover the small capsule and push down gently until locked in place
• Oral: (HICON(R) capsule) Store the capsule in a suitable polypropylene container and place inside a lead pot until use; use capsule within 7 days

• Hicon: Oral Kit:

• Hyperthyroidism: Prior to administration: Obtain a CBC within 1 month of therapy. If leukopenia or thrombocytopenia is identified, use dosimetry to determine a safe sodium iodide I 131 activity that delivers less than 2 Gy to the bone marrow .
• Hyperthyroidism: Prior to administration: Patients should maintain a low-iodide diet 2 weeks before administration and continue for several days during the uptake or imaging process
• Hyperthyroidism: Prior to administration: For severely hyperthyroid patients , discontinue antithyroid therapy 3 or 4 days before administration
• Hyperthyroidism: Prior to administration: Obtain a pregnancy test in females of reproductive potential to verify the absence of pregnancy .
• Hyperthyroidism: Prior to administration: In patients with a history of renal impairment, evaluate renal function for therapeutic planning and consider dosimetry .
• Hyperthyroidism: Before, during, and after administration: Patients should fast at least 2 hours before and 2 hours after administration , hydrate before and after administration , and void frequently .
• Hyperthyroidism: 148 to 370 megabecquerels (4 to 10 milliCuries) orally; individualize dose based on thyroid gland uptake and size of the gland
• Radionuclide thyroid imaging, for evaluation of thyroid function: (average patient, 70 kg) for thyroid uptake: 0.185 to 0.555 megabecquerels (5 to 15 microCuries) ORALLY
• Radionuclide thyroid imaging, for evaluation of thyroid function: (average patient, 70 kg) for scintiscanning: 1.85 to 3.7 megabecquerels (50 to 100 microCuries) ORALLY
• Thyroid cancer: (Iodotope(R) or Sodium Iodide I 131 capsules or solution (Mallinckrodt)) Prior to administration: Consider the administration of beta-blocker therapy to minimize the risk of hyperthyroidism and thyroid storm
• Thyroid cancer: (Iodotope(R) or Sodium Iodide I 131 capsules or solution (Mallinckrodt)) Ablation of residual postoperative thyroid tissue, 1850 megabecquerels (50 milliCuries) orally
• Thyroid cancer: (Iodotope(R) or Sodium Iodide I 131 capsules or solution (Mallinckrodt)) Therapeutic dosage, 3700 to 5550 megabecquerels (100 to 150 milliCuries) orally
• Thyroid cancer: (Iodotope(R) or Sodium Iodide I 131 capsules or solution (Mallinckrodt)) Individualize dosages based on patient-specific factors including nature of the underlying condition, co-morbidities, age, thyroid gland uptake and size, and the ability of the patient to comply with the therapeutic regimen
• Thyroid cancer: (HICON(R)) Prior to administration: Obtain a CBC within 1 month of therapy. If leukopenia or thrombocytopenia is identified, use dosimetry to determine a safe sodium iodide I 131 activity that delivers less than 2 Gy to the bone marrow .
• Thyroid cancer: (HICON(R)) Prior to administration: Patients should maintain a low-iodide diet 2 weeks before administration and continue for several days during the uptake or imaging process
• Thyroid cancer: (HICON(R)) Prior to administration: Discontinue antithyroid therapy 3 days before administration
• Thyroid cancer: (HICON(R)) Prior to administration: Obtain a pregnancy test in females of reproductive potential to verify the absence of pregnancy .
• Thyroid cancer: (HICON(R)) Prior to administration: In patients with a history of renal impairment, evaluate renal function for therapeutic planning and consider dosimetry .
• Thyroid cancer: (HICON(R)) Before, during, and after administration: Patients should fast at least 2 hours before and 2 hours after administration, hydrate before and after administration , and void frequently .
• Thyroid cancer: (HICON(R)) Usual dosage range, initial treatment: 1100 to 3700 megabecquerels (30 to 100 milliCuries) given orally; individualize dose based on thyroid gland uptake and size of the gland . The dosage must be individualized for each patient..
• Thyroid cancer: (HICON(R)) Usual dosage range, subsequent ablation of metastases: 3700 to 7400 megabecquerels (100 to 200 milliCuries)
• Thyroid cancer: Individualize dose based on thyroid gland uptake and size of the gland
• Thyroid cancer, metastases localization; Diagnosis: (average patient, 70 kg) 37 megabecquerels (1000 microCuries) ORALLY

• General Dosage Information: Safety and efficacy not established in pediatric patients