Sodium iodide I 131

In the U.S.

• Iodotope

Available Dosage Forms:

• Capsule
• Kit
• Solution

Therapeutic Class: Diagnostic Agent, Thyroid Function

Sodium iodide I 131 is used to treat hyperthyroidism (an overactive thyroid) and certain kinds of thyroid cancer. sodium iodide i 131 is taken up mainly by the thyroid gland. In the treatment of overactive thyroid gland, the radiation from the radioactive iodine damages the thyroid gland to bring its activity back down to normal. Larger doses of radioiodide are usually used after thyroid cancer surgery to destroy any remaining diseased thyroid tissue or to destroy thyroid cancer that has spread to other tissues.

When very small doses are given, a measure of the radioactivity taken up by the gland helps your doctor decide whether your thyroid gland is working properly or to locate tumors caused by certain types of thyroid cancers.

sodium iodide i 131 is to be given only by or under the direct supervision of a doctor with specialized training in nuclear medicine or radiation oncology.

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For sodium iodide i 131, the following should be considered:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to sodium iodide i 131 or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

Pediatric

Appropriate studies have not been performed on the relationship of age to the effects of sodium iodide I 131 capsules or solution in the pediatric population. Safety and efficacy have not been established.

Geriatric

Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of sodium iodide I 131 capsules or solution in the elderly. However, elderly patients are more likely to have age-related kidney or heart problems, which may require caution and an adjustment in the dose for patients receiving sodium iodide I 131 capsules or solution.

Pregnancy

Breast Feeding

Studies in women breastfeeding have demonstrated harmful infant effects. An alternative to this medication should be prescribed or you should stop breastfeeding while using sodium iodide i 131.

Interactions with Medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of sodium iodide i 131. Make sure you tell your doctor if you have any other medical problems, especially:

• Asthma or
• Sulfite allergy, history of—sodium iodide i 131 contains sodium bisulfite, which can make these conditions worse.

• Diarrhea or vomiting or
• Thyroid cancer, medullary or anaplastic—Should not be used in patients with these conditions unless determined by your doctor.

• Heart disease or
• Neck or throat blockage problems (eg, esophagus, trachea, or blood vessels in the neck)—Use with caution. May make these conditions worse.

• Kidney disease—Use with caution. The effects may be increased because of slower removal of the medicine from the body.

Sodium Iodide I 131 Solution Therapeutic is indicated for the treatment of hyperthyroidism and thyroid carcinomas that take up iodide. Palliative effects may be observed in patients with advanced thyroid malignancy if the metastatic lesions take up iodide.

Radiation Safety

Sodium Iodide I 131 Solution emits radiation and must be handled with safety measures to minimize inadvertent radiation exposure to clinical personnel and patients [see Warnings and Precautions (5.7)].

• Radiopharmaceuticals should be used only by or under the direction of phy­sicians 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.
• Wear waterproof gloves during the entire sodium iodide I-131 solution handling and administration procedure.
• Maintain adequate shielding during the radiation-emitting life of the product.
• Measure the patient dose using a suitable radioactivity calibration system immediately prior to administration.

Hyperthyroidism

For hyperthyroidism, the usual sodium iodide I-131 dose range is 148 to 370 MBq (4 to 10 mCi).  Higher doses may be necessary for the treatment of toxic nodular goiter and other special situations.  Consider discontinuation of anti-thyroid therapy in a severely hyperthyroid pa­tient three to four days before administration of sodium iodide I-131.  Evaluate patients for risk of thyroid enlargement and obstruction of structures in the neck [see Warnings and Precautions (5.1, 5.2)].

Thyroid Carcinoma

For thyroid carcinoma, the usual sodium iodide I-131 therapeutic dose is 3700 to 5550 MBq (100 to 150 mCi).  For ablation of post-operative residual thyroid tissue, the usual dose is 1850 MBq (50 mCi).

Individualization of Therapy

Individualize sodium iodide I-131 therapy, including dose selection, based upon patient-specific factors such as the nature of the underlying condition, co-morbidities, age, estimated thyroid tissue iodine uptake, thyroid size, as well as ability of the patient to comply with the therapeutic regimen and radiation safety procedures.  Perform a clinical assessment, including history, physical examination and laboratory testing when preparing patients for sodium iodide I-131 therapy in order to detect conditions which may alter thyroid iodine uptake and increase the risks of the therapy or diminish its effectiveness.  For example, intake of iodine in radiographic contrast may diminish thyroid iodine uptake while low serum chloride or nephrosis may increase thyroid iodine uptake.  Obtain a drug history and ascertain whether any medications need to be withheld before the administration of the therapy [see Drug Interactions (7)].

Radiation Dosimetry

The estimated absorbed radiation doses1 to an average (70 kg) euthyroid (normal functioning thy­roid) patient from an oral dose of iodine-131 in both milligray (mGy) per megabecquerel (MBq) and rad per millicurie (mCi) are shown in Table 1.

Table 1.  Absorbed Radiation Doses

Radiation-induced Thyroiditis

Sodium iodide I-131 may cause thyroiditis with gland enlargement and release of thyroid hormone, particularly when used to treat hyperthyroidism.  The thyroiditis may cause or worsen hyperthyroidism and may cause thyroid storm.  When treating hyperthyroidism, consider pre-treatment with anti-thyroid medication to help deplete the thyroid hormone content within the gland.  Discontinue the anti-thyroid medication at least three days before administration of sodium iodide I-131.  Consider beta-blocker therapy before administration of sodium iodide I-131 to minimize the risk of hyperthyroidism and thyroid storm.  

Thyroid-stimulating Hormone (TSH) and Thyroid Enlargement

Enhanced TSH secretion, e.g., following discontinuation of anti-thyroid medications, or the administration of TSH to enhance sodium iodide I-131 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 before preparative treatments known to cause thyroid enlargement. 

Radiation-induced Toxicities

Radiation-induced toxicities, including dose-dependent fatalities, have been reported following sodium iodide I-131 therapy.  Post-marketing reports have identified an increased risk for neoplasia, as well as risks for hematopoietic suppression.  Salivary and lacrimal gland toxicity is relatively common and may manifest as conjunctivitis, xerophthalmia, epiphora, sialadenitis and xerostomia [see Adverse Reactions (6)].

Hypersensitivity Reactions

Hypersensitivity reactions, including rash and hives, have been reported following administration of sodium iodide I-131. Sodium Iodide I 131 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 prevalence 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 the pre-therapy assessment, question patients about a history of hypersensitivity to sulfite [see Adverse Reactions (6)].

Fetal Risk

Transplacental passage of sodium iodide I-131 can cause severe and possibly irreversible hypothyroidism in neonates [see Contraindications (4)]. 

Females and Males of Childbearing Potential

When planning sodium iodide I-131 therapy for women of childbearing potential, obtain a pregnancy test and verify the absence of a pregnancy.  Advise women and men of childbearing potential to use two effective methods of contraception to avoid pregnancy for at least six months after sodium iodide I-131 administration.  Advise patients of the potential need to use two effective forms of contraception to avoid pregnancy for an even longer period of time (e.g., one year) if additional sodium iodide I-131 therapy or radionuclide imaging is anticipated. 

Transient Infertility

Transient, dose-related impairment of testicular function has been reported after sodium iodide I-131 therapy.  Consider sperm banking for men who are anticipated to receive a high cumulative sodium iodide I-131 dose (e.g., greater than 14 GBq). 

In females, transient ovarian failure has been observed after sodium iodide I-131 therapy.

Radiation Exposure Risk to Other Individuals

Unwanted radiation exposure can occur from handling and administration of radiopharmaceuticals or from contaminated waste products, including urine and feces.  Follow safe administration instructions to minimize unnecessary radiation exposure to patients and health care workers [see Dosage and Administration (2.1)]. Instruct patients on how to reduce unnecessary radiation exposure to others, especially family members following treatment.

Review the most recent professional society guidelines and publications that describe the procedures for the safe use of sodium iodide I-131 therapy to minimize radiation toxicity risks to patients, radiation exposure risks to other individuals, and environmental radiation contamination risks.   

In case of exposure to a radioactive dose of sodium iodide I-131 exceeding the intended therapeutic dose provide general supportive care, monitor for bone marrow and thyroid suppression and consider administering a thyroid blocking agent such as potassium iodide (KI) or perchlorate promptly within 4 to 6 hours after the exposure. Thyroid blockade may reduce radiation exposure of thyroid tissue but would not prevent radiation injury to the rest of the body. Assess the benefit of administering a blocking agent against the risk of failure of sodium iodide I-131 therapy.

Mechanism of Action

Taken orally, sodium iodide I-131 is rapidly absorbed and distributed within the extracellular fluid of the body.  The iodide is concentrated in the thyroid via the sodium/iodide symporter, and subsequently oxidized to iodine.  The destruction of thyroidal tissue is achieved by the beta emission of sodium iodide I-131. 

Pharmacodynamics

The therapeutic effects of sodium iodide I-131 are a result of the ionizing radiation absorbed by the thyroidal tissue.  Tissue damage is the result of direct insult to molecules by ionization and excitation and the consequent dissociation of those molecules.  About 90% of local irradiation from sodium iodide I-131 is the result of beta radiation and 10% is the result of gamma radiation. 

Pharmacokinetics

After oral administration, sodium iodide I-131 is absorbed rapidly from the upper gastrointestinal tract (90% in 60 minutes). The pharmacokinetics follow that of unlabelled iodide.  After entering the blood stream, the iodide is distributed into the extra thyroidal compartment.  From here it is predominantly taken up by the thyroid or excreted renally. In the thyroid, the trapped iodide is oxidized to iodine and organified.  The sodium/iodide symporter (NIS) is responsible for the concentration of iodide in the thyroid.  This active transport process is capable of concentrating iodide 20 to 40 times the plasma concentration under normal circumstances, and this may increase tenfold in the hyperthyroid state. NIS also mediates active iodide transport in other tissues, including salivary glands, nasolacrimal duct, lacrimal sac, gastric mucosa, lactating mammary gland, and the choroid plexus.  The non-thyroidal iodide transporting tissues do not have the ability to organify accumulated iodide.

Depending on renal and thyroid gland function, urinary excretion is 37 to 75% of the administered dose, fecal excretion is about 10%, and excretion in sweat is almost negligible.   

Sodium Iodide I 131 Solution Therapeutic is supplied in shielded, screw-cap 15 mL vials that contain from 185 to 5550 MBq (5 to 150 mCi) iodine-131 at the time of calibration.  The expiration date is not later than one month after the calibration date. The calibration date and the expiration date are stated on the label. Do not use the product after the expiration date.

Storage

Store at a controlled room temperature of 20° to 25°C (68° to 77°F). Storage and disposal of Sodium Iodide I 131 Solution Therapeutic should be controlled in a manner that is in compliance with the appropriate regulations of the government agency authorized to license the use of this radionuclide.

The U.S. Nuclear Regulatory Commission has approved distribution of this radiopharmaceutical to persons li­censed to use byproduct material listed in 10 CFR 35.300, and to persons who hold an equivalent license issued by an Agreement State.

Review the most recent professional society guidelines and publications that describe important components of the patient counseling process. 

• Discuss the measures to minimize inadvertent radiation exposure to the patient, members of the patient’s household, the public, and the environment.
• Advise females and males of reproductive potential of the need to use two effective methods of contraception to avoid pregnancy for at least 6 months after I-131 administration due to fetal risk. Advise patients of the potential need to use two effective methods of contraception to avoid pregnancy for an even longer period of time (e.g., one year) if additional sodium iodide I-131 therapy and further radionuclide imaging is anticipated.
• Advise patients of the possibility of transient infertility and possible use of sperm banking for males of reproductive potential.
• Among lactating females, discuss the need to discontinue breastfeeding and pumping at least four weeks before administration of sodium iodide I-131. If sodium iodide I-131 is administered in the postpartum period, advise the lactating mother to not breast-feed her infant.

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© 2015 Mallinckrodt.

Manufactured by:                                                                                                           
Mallinckrodt Nuclear Medicine LLC
Maryland Heights, MO 63043

Made in USA

A450I0   

Rev 10/2015

Mallinckrodt™
Pharmaceuticals