Sodium Iodide

Sodium Iodide (131i)

Treatment option:

Medically reviewed

Last updated on 22/12/2025

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Sodium Iodide

What is Sodium Iodide? Overview

As a radiopharmaceutical agent, Sodium Iodide I-131 is a specialized, prescription-only medicine whose use is intrinsically linked to the function of the thyroid gland. It is a synthetic compound containing the radioactive isotope Iodine-131 (^131I) engineered for medical application.

Quick Facts	Description
Active ingredient	Sodium Iodide I-131
Form	Oral solution or Oral capsule
Pharmacological class	Radiopharmaceutical agent
Common use	Targeted therapy for thyroid tissue
Origin	Synthetic (produced via nuclear processes)

Composition and Classification

The active component is the radioactive isotope Sodium Iodide I-131, which functions as a single-active ingredient product intended for oral administration. This compound is a synthetic iodide salt that delivers a highly localized therapeutic effect. This medicine is characterized by its ability to target tissues that actively absorb iodine. Sodium Iodide I-131 is utilized because the thyroid's natural affinity for iodine allows for the selective concentration of the compound within the target tissue.

The medication is available as both an oral capsule and an oral solution suspended in an aqueous vehicle, offering flexibility in its delivery as a radiopharmaceutical preparation. Furthermore, this agent acts as both a diagnostic and therapeutic agent, relying on its radiation properties for both imaging and treatment purposes.

General Purpose

The general purpose of Radioactive Sodium Iodide is to serve as a targeted therapy agent. The core principle is thyroid trapping, where the compound is selectively concentrated within thyroid tissue and related abnormal cells. This unique characteristic allows the medication to exert its influence directly and locally on the tissue responsible for thyroid function. A typical, neutral use scenario involves a patient taking the preparation to influence the size or activity of specific thyroid tissue.

Regulatory References

What side effects are possible with Sodium Iodide?

Possible Side Effects and Safety Information

The safety profile for Sodium Iodide I-131, based on official regulatory documents, is organized by the frequency and severity of adverse reactions. The most significant risks are long-term, radiation-related effects, while common reactions are often localized and time-specific.

Common and Expected Adverse Reactions

Common side effects listed in regulatory labeling are often related to the local effects of radiation and include:

Hypothyroidism: The expected and often intentional long-term outcome of treatment.
Radiation-induced Thyroiditis: Localized neck pain, tenderness, or swelling, typically occurring around the third day after administration.
Sialadenitis: Inflammation and dysfunction of the salivary glands.
Glandular Dysfunction: Dysfunction of the lacrimal (tear-producing) glands.

Serious and Clinically Significant Adverse Reactions

Serious adverse events are typically rare but clinically significant and include:

Secondary Malignancies: Increased risk of developing Solid Cancers and Acute Leukemia has been documented.
Hematopoietic Suppression: Dose-dependent bone marrow depression, which can lead to deficiencies in blood cell production.
Thyrotoxic Crisis: Potential for severe exacerbation of existing hyperthyroidism.
Hypersensitivity: Rare reports of severe allergic reactions, including anaphylaxis.

Population-Specific Safety Restrictions

Sodium Iodide I-131 is subject to absolute safety restrictions for specific patient groups:

Pregnancy: The medicine is Contraindicated due to the high risk of severe and irreversible fetal hypothyroidism.
Lactation: It is Contraindicated; breastfeeding must be permanently discontinued.
Reproductive Potential: Transient infertility has been observed, and patients are advised to use contraception for a specified period post-treatment.

Overdose and Emergency Response

The official regulatory profile for Sodium Iodide I-131 focuses on the risks associated with excessive radiation exposure, as the acute clinical consequences of overdosage are not known or defined in labeling. If overdosage is suspected, the primary regulatory response is directed toward the support of all vital functions and the prompt institution of symptomatic therapy. No specific antidote is known for the radioactive component.

Immediate medical help must be sought for any sign of a severe reaction, such as difficulty breathing or swelling, occurring during or following administration. Emergency resuscitation equipment should be available. To manage overexposure and minimize the absorbed radiation dose, procedural steps are required, including maintaining hydration and ensuring frequent voiding to enhance the urinary elimination of the radioiodide.

Regulatory documents highlight that patients with impaired renal function and geriatric patients may be at increased risk of toxic reactions due to slower drug clearance. Monitoring of renal function is required for at-risk patients, and obtaining a complete blood count is a mandated follow-up procedure to check for potential hematopoietic suppression linked to excessive exposure.

Therapeutic Uses of Sodium Iodide

What Sodium Iodide Treats: Main Uses and Benefits

Sodium Iodide I-131 is commonly used for managing hyperthyroidism and is relevant for managing conditions where functional stability becomes affected due to thyroid cancers. Its main therapeutic applications include managing conditions that cause an overactive thyroid gland, such as Graves' disease and toxic goiters, and addressing papillary and follicular thyroid cancer (differentiated thyroid carcinoma).

The primary benefit is associated with its application in situations involving symptoms linked to organ-specific functional stress, which addresses the cause of symptomatic clusters related to heightened physiological activity. This treatment assists with the process that helps ease symptoms related to systemic imbalance, such as rapid heartbeat and tremors, which ultimately contributes to improved comfort and helps maintain functional stability. It is commonly applied after surgery as adjuvant therapy in clinical settings that involve acute or unstable symptom patterns and supports the patient during episodes of heightened discomfort.

Quick Fact: Support for Systemic Imbalance

This specialized radiopharmaceutical is commonly used for managing thyroid hyperactivity, and may assist with symptoms related to physiological strain and symptoms that interfere with daily functioning.

Eligibility and Restrictions for Use

Who Can and Cannot Use Sodium Iodide (Radioactive Iodide)

Official regulatory information strictly defines eligibility for Sodium Iodide therapy and diagnosis, primarily to manage radiation exposure risk and efficacy. The medication is contraindicated (must not be used) in several patient groups.

Absolute Contraindications

Population/Condition
Pregnancy (Due to risk of fetal harm)
Lactation/Nursing Mothers (Radioiodine is excreted in milk)
Known Hypersensitivity to the active substance or excipients
Certain Gastrointestinal Disorders (e.g., dysphagia, active ulcers)

Restrictions and Limitations

Population/Condition	Regulatory Status
Pediatric Patients (Children/Adolescents)	Safety and effectiveness not established; use requires special justification.
Renal Impairment	Caution required; dose adjustment may be necessary due to altered clearance and increased radiation risk.
Hepatic Impairment	Not formally studied; use requires careful consideration.
Geriatric Patients	Special consideration needed due to frequent underlying comorbidities.

Official labeling requires effective contraception for women of childbearing potential during and for a specified period after treatment. Use is also generally unsuitable for thyroid cancer types (e.g., medullary, anaplastic) that do not adequately absorb iodine.

What should I know about interactions with other medicines?

The interaction profile for Sodium Iodide I-131 is strictly defined by the necessity of radioiodide uptake into the thyroid tissue for therapeutic effect. Regulatory documents classify co-administration with two main medicinal product categories as restricted or contraindicated combinations due to competitive inhibition that significantly diminishes effectiveness.

Restrictions and Timing Rules

These restrictions apply to Anti-thyroid drugs (such as Methimazole or Propylthiouracil) and Thyroid Products (including Triiodothyronine). For this reason, mandatory timing separation is required; for example, anti-thyroid therapy often needs discontinuation for three to four days, and Triiodothyronine requires cessation for up to 14 days, as stated in regulatory labeling.

Interactions are also documented with Stable Iodine in any form, which encompasses certain supplements, high-iodine food, and Iodinated Contrast Media. The intake of these substances must be investigated and restricted prior to administration. Furthermore, Iodinated Contrast Agents may cause a pharmacokinetic interaction resulting in increased systemic exposure of the radioiodide due to reduced renal clearance.

Population and Management Notes

Official labeling notes that Renal Impairment is a population-specific condition that necessitates caution, as the slower elimination of the agent can lead to increased radiation exposure. Additionally, co-administration of agents like Beta-blockers is a documented strategy to manage the interaction outcome, mitigating the risk of aggravated hyperthyroidism following radioiodide treatment.

Mechanism of Action

How Sodium Iodide Works: Mechanism of Action

The action of Sodium Iodide I-131 is defined by its two-step mechanism: targeted accumulation followed by internal radiotoxicity.

Targeted Uptake via the NIS Transporter

The process begins by exploiting the cell's native functions. The drug utilizes the Sodium-Iodide Symporter (NIS), a specific membrane transport protein, to be actively transported and concentrated inside particular cells. This highly selective accumulation ensures the active agent is maximally delivered to the target tissue, setting the stage for its subsequent internal action.

Internal Radiotoxicity and DNA Destruction Cascade

Once concentrated, the core action is initiated by the radioactive decay of the Iodine-131 isotope, which releases high-energy beta (beta^-) particles within the cell. The resulting localized ionization and free radical generation cause irreparable damage to DNA and other essential cellular components. This direct cellular damage triggers widespread apoptosis and necroptosis.

Resulting Functional Tissue Ablation

The inevitable consequence of this irreversible cellular destruction is functional ablation. This means the specific cell population that concentrated the drug loses its function entirely due to mass cell death, leading to a permanent structural and functional alteration in the targeted tissue. The effective range of this mechanism is confined to a short distance (2–5 mm), confining the pharmacological action to the immediate vicinity.

Dosage and Administration Information

How to Use Sodium Iodide I-131 — Official Administration Guidelines

Sodium Iodide I-131 is a specialized radiopharmaceutical administered exclusively by oral route, typically as a capsule or a diluted solution. The dose is highly individualized based on the patient's condition, the size of the thyroid gland, and the gland’s uptake of radioiodide, as determined by a qualified physician prior to administration.

Official Administration Protocol

Administration Scope	Rule or Requirement
Route of Administration	Oral (Capsule or Diluted Solution)
Timing in Relation to Meals	Patients must fast at least 2 hours before and 2 hours after administration to ensure optimal absorption.
Preparation	The concentrated solution must be diluted with a specific diluent (e.g., Purified Water with 0.2% sodium thiosulfate) to ensure a stable pH (7.5–9.0) and prevent volatilization. The final dose must be measured immediately before use.
Age-Group Rules	In women of reproductive potential, the absence of pregnancy must be verified by testing prior to administration. Nursing mothers must discontinue lactation at least four weeks prior to therapy to minimize radiation dose to breast tissue.
Special Procedural Conditions	Patients must follow a low-iodide diet for two weeks before the procedure. Adequate hydration and frequent voiding are required after administration to enhance the elimination of unabsorbed radioiodide. Concurrent antithyroid therapy (e.g., propylthiouracil) is typically discontinued 3 to 4 days prior.

Official Step Sequence

Verify absence of pregnancy in females of reproductive potential.
Confirm patient adherence to a low-iodide diet and discontinuation of interfering drugs.
Prepare the dose by dilution or encapsulation, ensuring radiation safety and pH control.
Measure the final dose with a calibration system.
Administer the dose orally, ensuring the patient fasts for 2 hours before and 2 hours after.
Instruct the patient to hydrate and void frequently for enhanced radioiodide excretion.

This protocol ensures the single, specialized dose of Sodium Iodide I-131 is correctly prepared and administered under strictly defined conditions, optimizing target tissue uptake while managing radiation safety.

Recent Clinical Evidence

Research Evidence / Overview of Studies for Sodium Iodide

Sodium Iodide I-131 was studied for its use as a treatment with a long history, and authoritative regulatory documentation outlines the evidence base, including sources such as the U.S. Food and Drug Administration and the European Medicines Agency. Research has explored how the treatment influences two main categories of thyroid conditions.

Evidence for Use in Differentiated Thyroid Carcinoma (DTC)

Research has examined Sodium Iodide I-131 in patients with differentiated thyroid carcinoma (DTC), which includes papillary and follicular thyroid cancers. The treatment was studied for use after surgery for remnant ablation and to address cancer that was observed in studies to have spread. Large observational cohort studies have tracked patient outcomes over very long periods, often spanning several decades. Research examined important outcomes such as Overall Survival and Disease-Free Survival. Studies monitored the success of remnant ablation and measured biomarkers, such as Thyroglobulin (Tg), which are used in research contexts for monitoring disease status.

Evidence for Use in Hyperthyroidism Management

Sodium Iodide I-131 was evaluated in research for managing conditions characterized by functional imbalance, such as Graves' disease and toxic goiter. This research is built on systematic reviews and retrospective cohort studies that describe the long-term history of clinical use. These studies explored outcomes related to systemic or functional imbalance, such as the frequency with which patients reached a non-hyperactive thyroid functional state. Research examined the time needed for patients to reach this stability and studies monitored for the subsequent development of hypothyroidism, which was associated with this treatment in some studies.

What is Still Uncertain About Sodium Iodide I-131

Scientific reviews and major guidelines consistently highlight several areas where research remains insufficient. One key limitation is that comparative evidence is lacking from large, modern randomized controlled trials (RCTs). For DTC, limited information is available for establishing the optimal administered dosage for all patients, especially those with low-risk disease. Furthermore, due to the decades-long nature of the follow-up, research is ongoing to fully characterize all long-term effects, and some studies observed a pattern where use in younger patients was associated with the development of secondary cancers. Evidence quality varies across studies, and findings are often derived from institutional protocols rather than standardized, controlled trials.

Frequently Asked Questions (FAQ)

Common questions about Sodium Iodide (FAQ)

Q: What do I do if I vomit the capsule?

In situations where the dose is vomited, official product information indicates that patients should contact their healthcare provider immediately for guidance. Regulatory guidance may note that patients with conditions like active vomiting are typically evaluated carefully before administration, as vomiting could result in a significant loss of the intended dose.

Q: How long will I be radioactive after treatment?

The radioactive element in this medicine, Iodine I-131, has a physical half-life of just over eight days. The period during which the medication remains in the body is influenced by factors such as the administered dose, the patient’s thyroid function, and the rate at which the unabsorbed radioiodide is naturally eliminated. Patients are generally provided with specific radiation safety precautions and follow-up guidance from the administering clinic for a defined period after treatment.

Q: Can this be used to scan or image my thyroid, or is it only for treatment?

According to official regulatory documents, Sodium Iodide I-131 is used for both treatment (therapeutic use) and for scanning (diagnostic use). It is used to treat conditions like hyperthyroidism and thyroid carcinoma, and it is also used in a diagnostic capacity to perform the radioactive iodide (RAI) uptake test to evaluate how the thyroid is functioning.

Q: Why do I need to drink extra water after the procedure?

Regulatory labeling indicates that adequate fluid intake and frequent urination are generally recommended after the dose is administered. This procedure is intended to promote the rapid excretion of any radioiodide that was not absorbed by the thyroid gland, which helps to minimize the radiation exposure to other tissues.

Q: What other medications do I need to stop taking before treatment?

Official prescribing information advises that several categories of products must be discontinued or restricted before receiving Sodium Iodide I-131. These include anti-thyroid drugs, thyroid hormone products, and any form of stable iodine, such as supplements or iodinated contrast media. These substances must be stopped because they compete with the radioiodide, reducing the effectiveness of the treatment.

Q: How does Sodium Iodide I-131 actually kill the thyroid cells?

The action of the medication is based on localized radiation. After the thyroid tissue absorbs the compound, the Iodine I-131 isotope releases high-energy beta particles. This localized radiation may damage cellular components, which is the mechanism intended to lead to the functional ablation or destruction of the targeted thyroid tissue.

How should Sodium Iodide be stored and disposed of?

How to Store and Dispose of Sodium Iodide

The storage of Sodium Iodide I-131 is strictly defined by regulatory authorities to maintain product stability and safety.

Storage Requirements

Sodium Iodide must be stored at controlled room temperature, which is between 20 C to 25 C (68 F to 77 F). The product must be protected from light and kept in the original container, which should be kept tightly closed. For child safety, the medication must be stored out of the reach and sight of children.

Disposal Instructions

As a radiopharmaceutical agent, Sodium Iodide disposal requires special handling. Disposal of unused product or waste materials must be carried out in accordance with local and national regulations for radioactive waste. Consult a specialized healthcare professional for proper handling and discarding instructions.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

Available in countries:

Japan

Malta

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