sodium iodide I-131

Action and Spectrum

Actions and Spectrum: 

sodium iodide I-131 is a radioactive form of iodine used to treat thyroid diseases, including hyperthyroidism and certain types of thyroid cancer. It is administered orally and selectively taken up by thyroid tissue, emitting beta and gamma radiation that destroys thyroid cells. 

The action of sodium iodide I-131 is based on the principle of radiation therapy, which uses ionizing radiation to kill cancer cells or suppress the overactive function of the thyroid gland. The radiation from the iodine is absorbed by the thyroid tissue, leading to the destruction of the thyroid cells and the reduction of thyroid hormone production. 

sodium iodide I-131 has a relatively long half-life of 8.02 days, which allows for sustained radiation exposure to the thyroid tissue. The radiation is usually delivered as a single dose, although multiple doses may sometimes be given. 

The spectrum of action of sodium iodide I-131 is limited to the thyroid gland and adjacent tissues, where the iodine transport mechanism selectively takes it up. It is ineffective in treating other types of cancer or non-thyroid-related hyperthyroidism. 

Drug Interaction

Adverse Reaction

Frequency not defined 

Hypersensitivity 

Fetal toxicities 

Transient infertility 

Chest Pain 

Hyperthyroidism 

Thyrotoxic crisis 

Hyperparathyroidism 

Local swelling 

Sialadenitis 

Rash 

Itching 

Hives 

Black Box Warning

Contraindication / Caution

Contraindication/Caution: 

sodium iodide I-131 has several contraindications and precautions that should be considered before use. These include: 

• Pregnancy: sodium iodide I-131 can cause harm to a developing fetus, and therefore, it is contraindicated in pregnant women. 
• Breastfeeding: sodium iodide I-131 is excreted in breast milk and can harm nursing infants, hence is contraindicated in women who are breastfeeding. 
• Allergy or hypersensitivity: Patients with known allergies or hypersensitivity to iodine should not receive sodium iodide I-131. 
• Uncontrolled hyperthyroidism: Patients with uncontrolled hyperthyroidism may be at increased risk of developing thyroid storm if treated with sodium iodide I-131. 
• Active thyroiditis: Patients with active thyroiditis may experience an exacerbation of symptoms if treated with sodium iodide I-131. 
• Concurrent treatment with antithyroid medications: Antithyroid medications can interfere with the thyroid gland’s uptake of sodium iodide I-131 and should be discontinued before treatment with sodium iodide I-131. 
• Reduced kidney function: sodium iodide I-131 is excreted through the kidneys and may accumulate in patients with reduced kidney function, leading to an increased risk of side effects. 

Pregnancy / Lactation

Pregnancy consideration:  

The drug is not safe during pregnancy and is hence contraindicated. 

Breastfeeding warnings:  

The drug is excreted in breast milk, hence contraindicated during lactation. 

Pregnancy category: 

• Category A: Satisfactory and well-controlled studies show no risk to the fetus in the first or later trimester. 
• Category B: No evidence of risk to the fetus is found in animal reproduction studies, and there are not enough studies on pregnant women.    
• Category C: Adverse effects on the fetus found with evidence in animal reproduction studies and no adequate evidence for a human product; Pregnant women must take care of the potential risks. 
• Category D: There is adequate data with sufficient evidence of human fetal risk from various platforms. However, despite potential dangers may be used only in emergencies for potential benefits. 
• Category X: Drugs listed in this category outweigh the risks over benefits. The drug is not for pregnant women. 
• Category N: No data for the drug under this category is available. 

Pharmacology

Pharmacology: 

odium iodide I-131 is a radioactive form of iodine used to treat thyroid diseases, including hyperthyroidism and certain types of thyroid cancer. It is an orally administered radiopharmaceutical that emits beta and gamma radiation. It selectively targets thyroid tissue due to its high affinity for the sodium-iodide symporter on the thyroid follicular cells. 

Pharmacodynamics: 

The pharmacodynamics of sodium iodide I-131 is based on the principles of radiation therapy. It selectively targets the thyroid gland due to its high affinity for the sodium-iodide symporter on the thyroid follicular cells. Once inside the thyroid gland, it emits beta and gamma radiation that damages the DNA of the thyroid cells, leading to their destruction.  

Pharmacokinetics: 

Absorption 

sodium iodide I-131 is administered orally and absorbed in the gastrointestinal tract, primarily in the small intestine. Once absorbed, it is rapidly taken up by the thyroid gland, emitting beta and gamma radiation.  

Distribution  

sodium iodide I-131 is limited to the thyroid gland and surrounding tissues, such as the salivary glands and the parathyroid glands.  

Metabolism 

It is not metabolized in the body and is excreted through the urine over several days, with most of the radioactivity being excreted within the first 48 hours. 

Elimination and Excretion 

The elimination half-life of sodium iodide I-131 is approximately 8 days. Half of the administered dose is eliminated from the body within 8 days.  

Adminstartion

Administration: 

sodium iodide I-131 is typically administered orally as a capsule or a liquid solution. The sodium iodide I-131 is individualized based on the patient’s body weight, thyroid function, and the desired radiation dose to the thyroid gland.  

Before administration, patients may be required to adhere to a low-iodine diet for several days to reduce the amount of non-radioactive iodine in their bodies, which could compete with radioactive iodine uptake by the thyroid gland.  

Patients are usually instructed to fast for several hours before and after administration. The medication is then administered orally, usually as a single dose.  

After administration, patients may be advised to stay in isolation for several days to reduce radiation exposure to others. They may also be advised to increase fluid intake and to urinate frequently to reduce radiation exposure.  

Patients receiving sodium iodide I-131 may require close monitoring of their thyroid function, radiation exposure levels, and potential adverse effects. They may also be advised to avoid close contact with pregnant women and young children, as they may be more sensitive to radiation exposure. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: sodium iodide I-131 

Pronounced: so-dee-um-EYE-oh-dide 

Why do we use sodium iodide I-131? 

sodium iodide I-131 is primarily used to manage thyroid disorders, including hyperthyroidism and thyroid cancer. 

In treating hyperthyroidism, sodium iodide I-131 is used to destroy thyroid tissue that produces excess thyroid hormone selectively. After initial treatment, it is a preferred treatment option for patients with failed medical therapy or recurrent hyperthyroidism. sodium iodide I-131 effectively reduces thyroid hormone levels and controls hyperthyroid symptoms in most patients, and the treatment is usually well-tolerated. 

In managing thyroid cancer, sodium iodide I-131 is a targeted radiation therapy to destroy any remaining thyroid tissue after thyroidectomy (surgical removal of the thyroid gland).