Dosing and uses of Hicon (sodium iodide I-131)
Adult dosage forms and strengths
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 microCi (0.555 MBq)
- 25 microCi (0.925 MBq)
- 50 microCi (1.85 MBq)
- 100 microCi (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
4-10 mCi PO (148-370 MBq)
Toxic nodular goiters and other serious thyroid conditions may require larger dosages
Thyroid Cancer
Ablation of normal thyroid tissue: Initial dose of 30-100 mCi PO (1100-3700 MBq)
Subsequent metastases ablation: 100-200 mCi PO (3700-7400 MBq)
Thyroid Function Diagnostic
Indicated for use in performance of the radioactive iodide (RAI) uptake test to evaluate thyroid function
Diagnostic doses may also be employed in localizing metastases associated with thyroid malignancies
Thyroid uptake: 5-15 microCi PO (0.185-0.555 MBq)
Scintiscanning: 50-100 microCi PO (1.85-3.7 MBq)
Localization of extra-thyroidal metastases: 1000 microCi PO (37 MBq)
Dosing Considerations
Sodium iodide I 131 capsule USP (diagnostic - oral) is available in 100 mCi at time of calibration
Other activities of 2.03, 1.11, 0.61, and 0.33 MBq (55, 30, 16.5, and 9 mCi) are available by using the color-coded decay calendar provided or by calculation using the date and time of calibration
Calibration and expiration dates are listed on the container labeL
Administration
Must dilute the concentrated oral solution be ingesting
The recommended dosage for orally administered sodium iodide I-131 is based on the thyroid gland uptake as well as the size of the gland
Thyroidal uptake and size should be determined prior to treatment and may be useful in calculating the therapeutic dose to be administered to the individual patient
Hydrate before and after administration to assure rapid urinary elimination of the iodide that is not absorbed by the thyroid gland
Handle/prepare/store according to radionuclear drug safety standards
Radiopharmaceuticals should be used only by nuclear physicians and/or radiopharmacists who are qualified by training and experience in the safe use and handling of radionuclides, and whose experience and training have been approved by the appropriate governmental agency authorized to license the use of radionuclides
Preparation (oral capsules)
- The kit includes one large gelatin capsule and one small gelatin capsule for each dose prepared
- Each large capsule is empty and each small capsule contains approximately 300 mg of dibasic sodium phosphate anhydrous USP as the absorbing buffer
- Using the calibration date and radionuclidic concentration on the label of the product vial, calculate the required volume to produce the necessary dose in MBq or mCi
- Insert an unopened small capsule into the bottom half of the empty large capsule
- Withdraw the required volume of sodium iodide I-131 solution (maximum 150 mcL) from the vial and inject into the center of the small capsule, slip upper half of the large capsule and gently push down until locked
- Store the capsule in a suitable polypropylene container and place inside a lead pot until use; use within 7days
Preparation (diluted oral solution)
- Using the calibration date and radionuclidic concentration on the label of the product vial, calculate the required volume to produce the necessary dose in MBq or mCi
- Add diluent solution 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
Pediatric dosage forms and strengths
Safety and efficacy not established
Hicon (sodium iodide I-131) adverse (side) effects
Frequency not defined
Reported with doses for treatment of benign disease (eg, hyperthyroidism)
- Hypersensitivity reactions
- Increased radiation accumulation
- Fetal toxicities
- Exposure to breast tissue with lactation
- Transient infertility
- Gastrointestinal disorders: Sialadenitis
- Cardiac disorders: Chest pain and tachycardia
- Skin and subcutaneous tissue disorders: Iododerma, itching skin, rash, and hives
- Endocrine disorders: Hypothyroidism, hyperthyroidism, thyrotoxic crisis, hypoparathyroidism
- General disorders and administration site conditions: Local swelling
Reported with doses for treatment of malignant disease
- Blood and lymphatic system disorders including fatalities: Radiation sickness, bone marrow depression, anemia, leucopenia, thrombocytopenia, and blood dyscrasia
- Neoplasms benign, malignant and unspecified (including cysts and polyps): Leukemia and solid cancers
- Eye disorders: Lacrimal gland dysfunction
- Gastrointestinal disorders: Salivary gland dysfunction, nausea, vomiting
- Congenital, familial and genetic disorders: Congenital hypothyroidism and chromosomal abnormalities
- Cerebral Edema (patients with iodine-avid brain metastases)
- Radiation pneumonitis (patients with iodine-avid lung metastases)
- Pulmonary fibrosis (patients with iodine-avid lung metastases)
Warnings
Contraindications
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 iodide uptake, which include the majority of medullary and anaplastic carcinomas
- Patients receiving concurrent anti-thyroid therapy
Cautions
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 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 neck, pain on 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 increased risk of cancer; follow safe handling and administration to minimize radiation exposure to patient and healthcare providers
- Certain food or drugs may alter thyroid uptake of sodium iodide I 131 and diminish effectiveness; recent intake of stable iodide in any form, or the use of thyroid or anti-thyroid drugs may diminish thyroid uptake of sodium iodide I 131
- Radiation-induced toxicities
- Dose-dependent fatalities (bone marrow suppression, malignancy)
- Dose-dependent hematopoietic suppression which manifests as a 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 (e.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
Pregnancy and lactation
Pregnancy category: X
Lactation: Excreted in human milk during lactation; do not breast feed, substitute formula for breast feedings
To minimize the absorbed radiation dose to the breast tissue, breast-feeding and breast-pumping should be discontinued for at least 4 weeks before administration
Breast-feeding may resume with the birth of another child, if the mother does not receive sodium iodide I-131 during that postpartum period
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Hicon (sodium iodide I-131)
Mechanism of action
RadiopharmaceuticaL
Thyroid ablation: Destruction of thyroidal tissue is achieved by the beta emission of sodium iodide I-131 and a subsequent thyroid-specific inflammatory response, causing fibrosis and destruction of the thyroid over weeks to many months
Diagnostic: Shows thyroid iodide uptake as a measure of thyroid function
Absorption
Readily absorbed from GI tract after oral administration
Distribution
Primarily distributed within the extra-cellular fluid of the body It is trapped by the thyroid
Thyroid uptake of iodide is usually increased in hyperthyroidism and in goiter with impaired hormone synthesis, decreased in hypothyroidism, and normal-to-decreased in hypothyroidism receiving iodine
It is also concentrated by the stomach, choroid plexus, and salivary glands
Protein bound: None
Metabolism
Trapped iodide is oxidized to iodine and organically incorporated so rapidly that the iodide trap of the thyroid contains <0.2 % free iodide in comparison to the organically bound iodine
Elimination
Half-life: 8.04 days; decays by beta emission and associated gamma emission
Excretion: Primarily via kidneys; normal range of urinary excretion is 37-75 % of the administered dose, varying with the thyroid and renal function
