Sodium iodide (I-131) POLATOM: Uses, Dosage & Side Effects
A therapeutic radiopharmaceutical containing radioactive iodine-131, used in licensed nuclear medicine centers to treat differentiated thyroid cancer and hyperthyroidism, including Graves’ disease and toxic nodular goiter.
Sodium iodide (I-131) POLATOM is a therapeutic radiopharmaceutical that contains radioactive iodine-131 as its active ingredient. Supplied as hard capsules with activities ranging from 37 MBq to 7400 MBq, it is swallowed under the direct supervision of a nuclear medicine physician. The iodine-131 is selectively taken up by thyroid cells through the sodium-iodide symporter, where its beta radiation destroys overactive or malignant thyroid tissue while sparing most surrounding organs. It is established as first-line or adjuvant therapy for differentiated thyroid cancer (papillary and follicular carcinoma) and as a definitive treatment option for Graves’ disease, toxic multinodular goiter, and toxic adenoma. Because it is a radioactive medicine, handling, administration, and post-treatment patient management are strictly regulated and limited to licensed facilities.
Quick Facts: Sodium iodide (I-131) POLATOM
Key Takeaways
- Sodium iodide (I-131) POLATOM is a radioactive iodine capsule given as a single oral dose under nuclear medicine supervision; it delivers targeted beta radiation to thyroid tissue via the sodium-iodide symporter.
- It is approved to treat differentiated (papillary and follicular) thyroid cancer – for post-surgical ablation of thyroid remnants and treatment of iodine-avid metastases – and for benign hyperthyroidism, including Graves’ disease, toxic multinodular goiter, and toxic adenoma.
- Pregnancy and breastfeeding are absolute contraindications; a pregnancy test is mandatory in women of reproductive potential before administration, and conception should be avoided for at least 6–12 months after therapy.
- Lifelong hypothyroidism requiring levothyroxine replacement is an expected outcome in most patients, especially after thyroid cancer therapy and frequently after radioiodine ablation for Graves’ disease.
- Strict radiation safety instructions – including distance from children and pregnant contacts, toilet hygiene, fluid intake, and travel restrictions – must be followed for several days to weeks after treatment, and are determined by the administered activity and national regulations.
What Is Sodium iodide (I-131) POLATOM and What Is It Used For?
Sodium iodide (I-131) POLATOM is a medicinal product that contains sodium iodide in which a proportion of the iodine atoms have been replaced by the radioactive isotope iodine-131 (131I). Because the active ingredient is radioactive, the product is classified as a radiopharmaceutical and is regulated by both medicines authorities (such as the EMA and FDA) and radiation protection authorities (such as the IAEA, national atomic regulators, and European directives on radiation protection). The product is manufactured by the National Centre for Nuclear Research – POLATOM in Otwock, Poland, one of the main European producers of medical radionuclides.
Iodine is a natural trace element that is actively taken up by the thyroid gland as a building block for thyroid hormones (thyroxine and triiodothyronine). The thyroid gland accomplishes this by expressing a membrane protein called the sodium-iodide symporter (NIS), which imports iodide from the bloodstream into thyroid follicular cells against a concentration gradient. When a patient swallows radioactive iodine, the NIS treats it identically to ordinary dietary iodine: within hours, a large fraction of the administered dose is concentrated inside the thyroid. There it is oxidized, incorporated into thyroglobulin, and retained within the follicles for days to weeks, during which time its radioactive decay delivers radiation to the surrounding thyroid cells.
Iodine-131 decays with a physical half-life of approximately 8.02 days. Each decay event releases a beta particle (mean energy 192 keV, maximum 606 keV) and one or more gamma photons (principally 364 keV). The beta particles have a mean tissue penetration of about 0.4–0.8 mm, making them highly effective at destroying the thyroid follicular cells in which the iodine is concentrated, while sparing most surrounding structures. The accompanying gamma radiation allows external imaging (by gamma camera or SPECT) to verify that the iodine has been taken up by the intended target tissue and to identify any distant metastases that also concentrate iodine.
Sodium iodide (I-131) POLATOM is approved for the following therapeutic indications:
- Differentiated thyroid cancer (DTC): Following total or near-total thyroidectomy, I-131 is used for ablation of residual (remnant) thyroid tissue to reduce the risk of recurrence and to facilitate long-term follow-up with thyroglobulin measurements and whole-body iodine scans. It is also used as adjuvant therapy for patients with residual disease or intermediate-to-high-risk features, and as treatment for iodine-avid locoregional or distant metastases, including lung and bone metastases.
- Graves’ disease (diffuse toxic goiter): Radioactive iodine is one of the three definitive treatments for Graves’ disease, alongside antithyroid drugs and thyroidectomy. It progressively destroys the hyperactive thyroid gland and restores euthyroidism, most often via a transition to permanent hypothyroidism treated with levothyroxine.
- Toxic multinodular goiter: In this condition, one or more autonomously functioning nodules produce excess thyroid hormone. Radioactive iodine is preferentially concentrated in the hyperactive nodules, which are therefore selectively ablated while the suppressed surrounding parenchyma is relatively spared.
- Toxic adenoma: A single autonomously functioning nodule (Plummer’s disease) that can be treated with a targeted dose of I-131; the suppressed normal thyroid tissue usually recovers function afterwards.
- Non-toxic multinodular goiter (selected cases): In some centers, higher-activity I-131 is used to reduce the volume of large nontoxic goiters when surgery is contraindicated or refused.
The product is also used diagnostically in lower activities for whole-body iodine scintigraphy in the follow-up of thyroid cancer, although many centers now prefer iodine-123 or low-activity I-131 for pure diagnostic imaging to limit stunning of thyroid tissue before subsequent therapy. The therapeutic use, however, remains the principal indication for Sodium iodide (I-131) POLATOM.
The sodium-iodide symporter is most abundantly expressed in thyroid follicular cells. Smaller amounts of NIS are present in salivary glands, lactating breast tissue, gastric mucosa, and the choroid plexus, which explains some of the predictable side effects. Other organs lack significant NIS expression and are exposed only to a small gamma-radiation dose from iodine circulating in the blood. This combination of biological targeting and short-range beta radiation is what makes I-131 one of the oldest and most effective examples of targeted radionuclide therapy in medicine – it has been in clinical use since the 1940s.
What Should You Know Before Receiving Sodium iodide (I-131) POLATOM?
Contraindications
Several situations represent absolute or strong relative contraindications to Sodium iodide (I-131) POLATOM. Understanding these is essential before treatment is planned.
- Pregnancy: I-131 is absolutely contraindicated during pregnancy. Iodine-131 crosses the placenta freely. From approximately 10–12 weeks of gestation the fetal thyroid begins to concentrate iodine, and administration of therapeutic activities can result in severe or complete destruction of the fetal thyroid gland (fetal hypothyroidism/cretinism), and at high activities other developmental harm. In women of reproductive potential, a negative serum or urine pregnancy test within 72 hours of administration is mandatory.
- Breastfeeding: Radioactive iodine is actively concentrated in lactating breast tissue and excreted in milk, delivering very high thyroid doses to the infant. Breastfeeding must be permanently discontinued before I-131 therapy and not resumed during or after the current lactation cycle. Active lactation also increases the radiation dose to the mother’s own breast tissue; lactation should be suppressed for at least 6 weeks before elective therapy whenever possible.
- Hypersensitivity: Known hypersensitivity to sodium iodide or to any excipient of the product.
- Inability to comply with radiation safety: Patients who cannot follow written post-administration radiation protection instructions – for example due to severe cognitive impairment, uncontrolled incontinence, or social situations where separation from young children is impossible – may need an alternative treatment approach (surgery or antithyroid drugs).
- Uncontrolled vomiting or severe dysphagia: May prevent reliable oral administration and increase contamination risk; delayed until controlled or an alternative route/agent is considered.
Warnings and Precautions
After receiving Sodium iodide (I-131) POLATOM you will be a temporary source of radiation. The greatest risk is to pregnant women, infants, and young children through close contact. Your nuclear medicine team will give you detailed written instructions on distance, sleeping arrangements, toilet hygiene, travel, work, and waste management, tailored to the activity you received and local regulations. Follow these instructions exactly; they are designed to keep exposure to family members and the public well below internationally recommended limits.
Before and during treatment with I-131, inform your nuclear medicine physician if any of the following apply to you:
- Large or compressive goiter: In patients with a large goiter, radiation-induced inflammation can cause transient swelling and may in rare cases worsen tracheal compression. Pretreatment with corticosteroids may be considered, and surgery may be preferred for very large goiters.
- Graves’ orbitopathy (thyroid eye disease): Radioactive iodine can worsen or precipitate Graves’ orbitopathy, particularly in smokers and in patients with active moderate-to-severe disease. Pretreatment and concomitant oral corticosteroids are routinely recommended in patients at risk. Active, severe eye disease is usually a reason to defer I-131 or prefer another modality.
- Recent high dietary or pharmacological iodine exposure: Iodinated contrast media (from CT or angiography), amiodarone, and iodine-rich supplements (kelp, seaweed, povidone iodine) can saturate the thyroid iodide pool for weeks to months and markedly reduce the effectiveness of I-131 therapy. Your team will ask about these exposures and may delay treatment or measure urinary iodine.
- Thyroid storm and severe thyrotoxicosis: In very active hyperthyroidism, destruction of thyroid cells by I-131 can transiently release stored hormone and worsen thyrotoxic symptoms. Elderly patients and those with cardiac disease are particularly vulnerable; antithyroid drugs are often used to achieve near-euthyroidism before and/or after therapy.
- Renal impairment: I-131 is cleared primarily by the kidneys. In significant renal dysfunction, whole-body retention increases, as does radiation dose to the bone marrow and other organs. Dose adjustment and prolonged isolation may be needed.
- Bone marrow reserve: Previous chemotherapy, external beam radiotherapy, or repeated high-activity I-131 therapy for metastatic thyroid cancer may reduce bone marrow reserve and increase the risk of myelosuppression.
- Salivary gland disease: Preexisting dry mouth (for example after head-and-neck radiotherapy, Sjögren’s syndrome, or previous I-131 therapy) may be aggravated. Measures to stimulate salivary flow (hydration, chewing gum, lemon sweets) from a few hours after administration can help.
- Lung metastases: Patients with diffuse pulmonary metastases from differentiated thyroid cancer that concentrate iodine are at increased risk of radiation pneumonitis and long-term pulmonary fibrosis, particularly when repeated high activities are used. Dosimetry-guided dosing is recommended in these patients.
- Urinary or fecal incontinence: Increases the risk of contamination of the patient, carers, and environment. Additional precautions (catheterization, absorbent pads, separate toilet, extended isolation) may be required.
You should be prepared to avoid most close physical contact with young children and pregnant women for a period defined by your team (often 5–14 days), to sleep alone, and to maintain good bathroom hygiene (sit to urinate, flush twice, wash hands thoroughly, drink plenty of fluids). Written, individualized instructions are always provided.
Other Medications
Tell your doctor about every medicine you are taking, including prescription drugs, over-the-counter products, herbal supplements, and any radiographic contrast agents or nuclear medicine scans you have had in the past 6 months. Many medicines and supplements affect thyroid iodine uptake and must be stopped or adjusted before radioactive iodine therapy.
Pregnancy, Breastfeeding and Fertility
Pregnancy must be excluded before every administration of Sodium iodide (I-131) POLATOM in women of reproductive potential. In practice, the combination of a careful menstrual history and a serum or urine hCG test obtained within 72 hours of treatment is used, together with documented effective contraception in the weeks before therapy.
After I-131 therapy, women should avoid becoming pregnant for a defined interval. International guidelines typically recommend waiting at least 6 months after treatment for benign hyperthyroidism and at least 6–12 months after therapy for differentiated thyroid cancer, to allow complete recovery of thyroid function, stable levothyroxine dosing, normalization of ovarian function, and confirmation of disease control. Individual advice will depend on the activity administered and the clinical context.
Breastfeeding must be permanently stopped before therapeutic I-131 and cannot be resumed during the current lactation cycle. For subsequent pregnancies, breastfeeding is possible as usual.
Men treated with high cumulative activities of I-131 for metastatic thyroid cancer may have transient impairment of spermatogenesis and, rarely, persistent infertility. Sperm cryopreservation should be discussed before repeated or very high-activity therapy. For standard single-dose treatments of hyperthyroidism, the effect on male fertility is clinically negligible. Men are advised to avoid fathering a child for at least 4 months after therapy.
Driving and Operating Machinery
Sodium iodide (I-131) POLATOM itself has no significant acute effect on attention, coordination, or psychomotor performance. Driving is therefore not restricted on pharmacological grounds. However, some patients experience transient fatigue or mild nausea in the first day or two after administration, and in some countries specific rules apply to passengers sharing long enclosed spaces (for example long taxi rides or flights) during the first days after treatment. Your team will advise on any practical restrictions.
Preparation Before the Treatment
Effective preparation is essential to maximize iodine uptake into the thyroid and maximize the therapeutic effect. Typical preparation includes:
- Low-iodine diet: For 1–2 weeks before therapy, particularly before thyroid cancer ablation, patients avoid iodized salt, dairy products, seafood, seaweed, egg yolks, and iodine-containing supplements. This “iodine depletion” increases the fractional uptake of I-131 by thyroid tissue.
- Withdrawal or adjustment of thyroid medication: For thyroid cancer ablation, either levothyroxine is withdrawn for 3–4 weeks (or liothyronine for 2 weeks) to allow endogenous TSH to rise above 30 mIU/L, or recombinant human TSH (rhTSH, thyrotropin alfa) is given on two consecutive days before I-131. For hyperthyroidism, antithyroid drugs are usually stopped several days before therapy and resumed a few days afterwards, depending on the indication and clinical severity.
- Fasting on the day of administration: The capsule is usually swallowed after a fasting period of 2–4 hours and food is avoided for a further 1–2 hours to ensure rapid and complete absorption.
- Hydration and salivary stimulation: High fluid intake before and after treatment reduces the radiation dose to the bladder and gonads. Starting about 24 hours after administration, frequent sour candies, chewing gum, or lemon juice can stimulate salivary flow and may reduce the incidence of sialadenitis.
How Does Sodium iodide (I-131) POLATOM Interact with Other Drugs?
Because I-131 works through a normal physiological transport mechanism, its efficacy is exquisitely sensitive to anything that changes the body’s iodine pool or thyroid-cell biology. Many of the clinically important interactions therefore relate to medication-induced reductions in thyroid iodine uptake rather than to the typical pharmacokinetic mechanisms of small-molecule drugs. Inform your nuclear medicine team about every medicine, contrast agent, supplement and topical product you have used in the previous months.
Major Interactions
| Interacting Substance | Effect | Clinical Management |
|---|---|---|
| Methimazole, carbimazole, propylthiouracil (thionamides) | Reduce thyroid hormone synthesis and can decrease I-131 retention | Typically stopped 3–7 days before therapy and resumed 3–7 days after in Graves’ disease |
| Amiodarone | Contains large amounts of iodine; causes severe and prolonged saturation of the thyroid iodine pool | I-131 therapy usually ineffective for 6–12 months or more; alternative treatment often preferred |
| Iodinated radiographic contrast media (CT, angiography, myelography) | Transient but substantial block of thyroid iodide uptake | Delay I-131 for at least 4–8 weeks; urinary iodine measurement may guide timing |
| Iodine-rich supplements (kelp, seaweed, multivitamins with iodine, iodine tinctures, povidone iodine) | Increase stable iodine pool and reduce I-131 uptake | Stop at least 2–4 weeks before therapy; low-iodine diet for 1–2 weeks |
| Perchlorate and thiocyanate (including heavy smoking) | Competitive inhibitors of the sodium-iodide symporter | Avoid perchlorate medications; smoking cessation advised before therapy |
| Levothyroxine and liothyronine | Suppress endogenous TSH and therefore reduce I-131 uptake in thyroid cancer ablation | Either withdraw (4 weeks levothyroxine / 2 weeks liothyronine) or replace with recombinant human TSH |
Minor and Practical Interactions
| Interacting Substance | Effect | Clinical Management |
|---|---|---|
| Lithium | Decreases release of iodine from the thyroid, prolonging intrathyroidal retention of I-131 | Occasionally used as an adjuvant to enhance therapeutic effect; requires lithium level monitoring |
| Beta-blockers (propranolol, atenolol, metoprolol) | Control adrenergic symptoms of hyperthyroidism; no interference with iodine uptake | Usually continued through therapy and tapered as thyrotoxicosis resolves |
| Glucocorticoids (prednisolone) | No significant effect on iodine uptake; protective in Graves’ orbitopathy | Often co-prescribed in eye-disease-prone patients during and after therapy |
| Proton pump inhibitors and antacids | Changes in gastric pH may slightly delay capsule dissolution and absorption | No routine adjustment; good hydration and fasting status are usually sufficient |
| Tyrosine kinase inhibitors (e.g., selpercatinib, lenvatinib, cabozantinib) | May redifferentiate iodine-refractory thyroid cancer and restore iodine uptake | Specialized use in clinical trials to re-sensitize tumor to I-131 |
In practice, a careful preparation checklist that covers diet, medications, supplements, and contrast history is more important for I-131 therapy than for most conventional drugs. A single poorly timed CT scan with iodinated contrast can waste an entire ablation dose, so your nuclear medicine team will review your medical records in detail and may request urinary iodine measurement if there is any doubt.
What Is the Correct Dosage of Sodium iodide (I-131) POLATOM?
Sodium iodide (I-131) POLATOM is supplied as single-use hard capsules with a wide range of labeled activities (from 37 MBq for small diagnostic or low-dose therapeutic applications up to 7400 MBq for high-dose cancer therapy). The exact activity administered is determined by the nuclear medicine physician, based on the indication, patient body size, thyroid volume, 24-hour radioiodine uptake, results of prior imaging, and, for metastatic disease, dosimetric calculations that estimate the dose to tumor and to critical organs (bone marrow, lungs). Always verify the indication and activity with your treating team – the figures below are typical ranges and not individual prescriptions.
Hyperthyroidism (Graves’ Disease, Toxic Nodular Goiter, Toxic Adenoma)
Graves’ Disease
Typical activity: Fixed dose of 370–600 MBq (approximately 10–16 mCi), or calculated dose aiming at 80–120 µCi per gram of thyroid tissue corrected for 24-hour uptake
Aim: Complete or near-complete ablation of the thyroid gland with deliberate induction of hypothyroidism, accepted as the most reliable cure strategy
Follow-up: Thyroid function tests every 4–6 weeks for the first 6 months; levothyroxine replacement is typically started when overt or persistent hypothyroidism develops.
Toxic Multinodular Goiter
Typical activity: Fixed 400–800 MBq or calculated dose of 100–200 µCi per gram of functioning thyroid tissue; higher activities are often needed than for Graves’ disease because uptake is usually lower
Aim: Achieve euthyroidism, reduce goiter volume, and treat hyperthyroidism; complete hypothyroidism is less frequent than in Graves’ disease
Notes: Recombinant human TSH stimulation is used in some centers to increase uptake in suppressed extranodular tissue and enhance volume reduction.
Toxic Adenoma (Plummer’s Disease)
Typical activity: 400–800 MBq, aiming to deliver a high dose to the autonomous nodule
Aim: Selective destruction of the hyperfunctioning nodule; the surrounding suppressed thyroid tissue typically recovers, and long-term hypothyroidism rates are relatively low (around 10–20%)
Differentiated Thyroid Cancer
Post-Surgical Remnant Ablation
Typical activity: 1.1–3.7 GBq (1100–3700 MBq; 30–100 mCi)
Indication: Ablation of small postoperative thyroid remnants in low-risk differentiated thyroid cancer
Preparation: Either levothyroxine withdrawal to achieve TSH >30 mIU/L or recombinant human TSH; low-iodine diet for 1–2 weeks
Adjuvant Therapy (Intermediate / High-Risk Disease)
Typical activity: 3.7–5.6 GBq (3700–5600 MBq; 100–150 mCi)
Indication: Known or suspected microscopic residual disease after surgery, aggressive histology, or extrathyroidal extension
Therapy for Iodine-Avid Metastatic Disease
Typical activity: 5.6–7.4 GBq (5600–7400 MBq; 150–200 mCi), with dosimetry-guided adjustment in some centers
Indication: Iodine-avid locoregional recurrence, lymph node, lung, or bone metastases demonstrated on pretherapy scan
Repeat therapy: Usually no sooner than 6–12 months between high-activity treatments, with monitoring of response (thyroglobulin, imaging) and cumulative bone-marrow dose. A common ceiling for lifetime cumulative activity is around 22–37 GBq (600–1000 mCi), though this is not absolute.
Dose Adjustments
Activity may be modified in the following situations:
- Renal impairment: Reduced whole-body clearance increases the dose to normal tissues. Activity is often reduced, and a longer hospitalization period is planned. Dialysis patients require specialized dosimetry and coordination with the nephrology team.
- Elderly patients: The risk of transient worsening of thyrotoxicosis is greater; many centers use antithyroid drug pretreatment and, for Graves’ disease, a somewhat higher fixed activity to maximize the likelihood of definitive cure.
- Extensive lung metastases: Dosimetry is strongly recommended to keep the whole-body retention at 48 hours below 4.4 GBq (120 mCi) and the lung dose below defined thresholds to prevent radiation pneumonitis and fibrosis.
- Previous I-131 therapy: Cumulative bone-marrow dose is tracked; repeat cycles may require activity reduction or longer interval, especially when prior blood count suppression has been observed.
Children and Adolescents
Radioactive iodine is used in pediatric patients only by specialist teams and most often for thyroid cancer. Activities are weight-adjusted and are deliberately reduced compared with adults because of the greater lifetime risk of secondary cancers from radiation exposure. For benign hyperthyroidism in children, antithyroid drugs are usually preferred as first-line therapy, with I-131 or surgery reserved for treatment failure, adverse reactions to medication, or patient and family choice. Routine use of I-131 is not recommended in children under 5 years.
Missed Dose
Because Sodium iodide (I-131) POLATOM is administered as a one-time dose in a controlled hospital or clinic setting, the concept of a missed dose does not apply in the usual sense. If an appointment is missed, the capsule is not dispensed. If the treatment is postponed, the activity of the capsule that was originally dispensed may no longer match the prescription because I-131 decays by approximately 8.3% per day; your team will recalculate and, if necessary, order a new capsule of appropriate activity.
Overdose and Contamination
True pharmacological overdose is very rare because each capsule is individually calibrated and dispensed by a radiopharmacist. If a higher-than-planned activity is accidentally administered, the priority is to limit thyroid and whole-body radiation dose. Measures may include:
- Immediate blockade of the thyroid with stable iodine (potassium iodide) if thyroid tissue is still present – most effective if given before or within a few hours after administration;
- Forced fluid intake and frequent voiding to accelerate renal clearance;
- Laxatives to reduce intestinal transit time and absorbed dose to the gut and adjacent organs;
- Sour candies, lemon juice, or chewing gum to stimulate saliva and reduce salivary gland dose;
- Notification of the competent radiation protection authority, as required by local regulations.
For contamination incidents (spillage, capsule damage), strict protocols are followed by the nuclear medicine department, including area decontamination, personal decontamination (shower, change of clothes), bioassay of exposed staff, and documentation in the radiation protection record.
How Sodium iodide (I-131) POLATOM Is Given
The capsule is dispensed from a lead container in a shielded room and handed to the patient, who swallows it directly with a glass of water under the supervision of the nuclear medicine physician or radiopharmacist. The staff do not touch the capsule with bare hands. Immediately after administration, the patient may be asked to rinse the mouth and drink additional water. Depending on activity and national regulations, patients may be discharged on the same day (typical for Graves’ disease and small ablation doses in some countries) or admitted to a specially shielded isolation room (typical for high-dose thyroid cancer therapy, often 1–4 days).
During the hospital stay, radiation measurements are taken to estimate the remaining activity in the body. Discharge is possible once the measured dose rate at 1 meter falls below the locally defined threshold (typically 25–40 µSv/h depending on jurisdiction). Written instructions, a treatment card, and contact details are given at discharge.
Sodium iodide (I-131) POLATOM is never dispensed for home self-administration. The capsule, its packaging, and any related waste remain subject to strict radiation protection legislation from manufacture through administration, storage, and disposal.
What Are the Side Effects of Sodium iodide (I-131) POLATOM?
Side effects of Sodium iodide (I-131) POLATOM reflect the biodistribution of iodine in the body rather than the traditional toxicity profile of a systemic drug. Tissues that express the sodium-iodide symporter – thyroid, salivary glands, gastric mucosa, and lactating breast – receive the highest radiation dose and account for most of the early effects. Other side effects relate to rapid destruction of thyroid tissue and the release of stored hormones. Most adverse events are mild, self-limiting, and manageable with simple supportive care.
Side Effects by Frequency
Very Common
May affect more than 1 in 10 people
- Hypothyroidism (often permanent and treated with levothyroxine) – expected outcome
- Transient radiation thyroiditis: neck pain, tenderness, or swelling 3–10 days after treatment
- Sialadenitis: painful swelling of parotid or submandibular glands
- Dry mouth (xerostomia), which may be transient or long-lasting
- Altered or metallic taste (dysgeusia) lasting days to several months
- Mild nausea and anorexia in the first 24–48 hours
- Fatigue for 1–4 weeks after treatment
- Transient bone-marrow suppression with mild reductions in white cell and platelet counts, particularly after high activities
Common
May affect up to 1 in 10 people
- Transient worsening of hyperthyroid symptoms in the first 1–2 weeks
- Radiation-induced gastritis (epigastric discomfort, nausea)
- Dry eyes and excessive tearing (dacryoadenitis) due to uptake in lacrimal glands
- Swelling in the neck from radiation thyroiditis, occasionally requiring short-course corticosteroids
- Worsening or new onset of Graves’ orbitopathy (more common in smokers and in active disease)
- Vomiting on the day of administration (rare but important because of contamination risk)
- Disturbed menstrual cycles for a few months
Uncommon
May affect up to 1 in 100 people
- Permanent xerostomia and long-term reduction in salivary flow
- Chronic dental problems (caries, oral candidiasis) secondary to dry mouth
- Persistent or severe taste disturbance
- Radiation cystitis or urethritis
- Salivary gland ductal obstruction (stricture, sialolithiasis)
- Transient hypoparathyroidism (usually after previous surgery rather than from I-131 itself)
- Mild, transient elevation of liver enzymes
Rare
May affect up to 1 in 1,000 people
- Severe bone-marrow suppression with clinically relevant anemia, leukopenia, or thrombocytopenia
- Radiation pneumonitis or pulmonary fibrosis in patients with diffuse iodine-avid lung metastases
- Severe or persistent vocal cord dysfunction
- Thyroid storm precipitated by release of stored hormone (predominantly in elderly or frail patients with severe thyrotoxicosis)
- Allergic reaction to excipients (very rare with modern formulations)
- Impaired fertility, particularly after high cumulative activities for metastatic cancer
Long-Term / Not Fully Quantified
Cumulative or long-term risks
- Small absolute increase in lifetime risk of secondary malignancies (including leukemia, stomach, bladder, breast, and salivary gland cancers), particularly after repeated high cumulative activities
- Progressive loss of lacrimal gland function in patients receiving multiple high-activity treatments
- Chronic salivary gland dysfunction contributing to dental and oral health problems
- Cardiovascular effects secondary to long-standing untreated hypothyroidism if replacement therapy is delayed or inadequate
Managing Common Side Effects
Simple supportive measures prevent or reduce many of the expected side effects. Starting about 24 hours after administration (not immediately, as this may increase early salivary gland dose), frequent sips of water, lemon sweets, sugarless chewing gum, or vitamin C tablets stimulate salivary flow and dilute the radioactivity in the salivary glands. Warm compresses and nonsteroidal anti-inflammatory drugs such as ibuprofen help with sialadenitis and radiation thyroiditis. Antiemetics can be prescribed for nausea. For patients at risk of worsening Graves’ orbitopathy, a 6–12 week course of oral or intravenous corticosteroids is given around the time of therapy.
Contact your nuclear medicine or endocrinology team urgently if you experience persistent severe neck swelling or difficulty breathing, uncontrollable vomiting, signs of worsening hyperthyroidism (fast heart rate, agitation, fever), sudden deterioration in vision or double vision, or symptoms suggestive of infection (fever, mouth sores, bleeding gums). Also report any incontinence or contamination incident for decontamination guidance.
You can report suspected adverse reactions to your national pharmacovigilance authority (for example the EMA in the European Union, the FDA MedWatch program in the United States, or the MHRA Yellow Card Scheme in the United Kingdom) and, where relevant, to the national nuclear regulator. Reporting helps improve knowledge of the long-term safety of therapeutic radiopharmaceuticals.
How Should Sodium iodide (I-131) POLATOM Be Stored?
Because Sodium iodide (I-131) POLATOM is an unsealed therapeutic radiopharmaceutical, its storage and handling are governed by radiation protection law in addition to normal pharmaceutical requirements. Storage takes place in a shielded vault or hot laboratory within a licensed nuclear medicine department. Typical conditions include:
- Temperature: Room temperature (below 25°C), unless the product label specifies otherwise.
- Light: Protection from direct sunlight, usually provided by the lead transport and storage containers.
- Shielding: Capsules are stored inside lead pots of appropriate wall thickness to reduce the external dose rate to below the limits defined in local legislation.
- Access: Restricted to authorized personnel who wear electronic dosimeters and observe time-distance-shielding principles.
- Expiry and calibration: Each capsule is labeled with a reference calibration date/time and an expiry date, because the activity decreases by approximately 8.3% per day. The capsule must be administered close to the planned calibration time to deliver the prescribed activity.
Patients are never asked to carry, store, or transport their own dose. If a patient is discharged soon after administration, they carry with them a “treatment card” documenting the date, activity, and contact information – useful in case of travel through radiation portal monitors (for example at airports or border crossings), where residual body radioactivity can trigger alarms for days to weeks.
Radioactive waste from patients (syringes, gloves, disposable items, urine collection bags for bedridden patients) is handled by the department’s radiation safety officer, stored in designated decay storage, and disposed of only after the activity has decayed to background levels or been transferred to a licensed waste contractor, in accordance with national regulations such as EU Directive 2013/59/Euratom and equivalent U.S. and other national frameworks.
What Does Sodium iodide (I-131) POLATOM Contain?
Active Substance
The active substance is sodium iodide (131I). Iodine-131 is a radioactive isotope of iodine produced by neutron irradiation of tellurium in a nuclear research reactor. The resulting iodine-131 is chemically identical to naturally occurring iodine-127 and, once dissolved as sodium iodide, is handled by the body in exactly the same way as dietary iodide. Each capsule is labeled with its calibrated activity (in MBq or GBq) at a specified reference time. Because I-131 decays with a physical half-life of 8.02 days, the activity in the capsule changes with time and must be recalculated by the radiopharmacist at the moment of administration.
Inactive Ingredients (Excipients)
The typical excipient composition of the hard capsule includes:
- Sodium thiosulfate pentahydrate (stabilizer and reducing agent that minimizes oxidation of iodide to volatile iodine)
- Disodium hydrogen phosphate dodecahydrate (buffer)
- Sodium bicarbonate or sodium hydroxide (for pH adjustment)
- Sucrose or mannitol (inert filler/carrier)
- Hard gelatin or hypromellose (HPMC) capsule shell, with food-grade colorant
Patients with known allergies to capsule shell ingredients (for example gelatin in vegetarian or religious contexts) should inform the nuclear medicine team, so that an alternative presentation or formulation can be arranged.
Appearance and Packaging
Sodium iodide (I-131) POLATOM is supplied as a single hard capsule contained inside a shielded lead container (the “pig”), itself placed in a labeled secondary container designed for transport of Class 7 radioactive material. The capsule shell is colored and printed to permit easy identification. The outer container carries the radioactive trefoil symbol, activity and calibration information, UN transport classification, and other regulatory labeling required by international agreements (for example IAEA TS-R-1 and ADR/RID/IATA transport rules).
Manufacturer and Marketing Authorization Holder
Sodium iodide (I-131) POLATOM is manufactured and marketed by the National Centre for Nuclear Research – POLATOM, Andrzeja Sołtana 7, 05-400 Otwock, Poland. POLATOM is one of the principal European producers of medical radionuclides and supplies radiopharmaceuticals under national marketing authorizations in multiple European countries. The radiation protection framework governing its use is harmonized under EU Directive 2013/59/Euratom and equivalent national regulations, in cooperation with the International Atomic Energy Agency (IAEA).
Frequently Asked Questions About Sodium iodide (I-131) POLATOM
Sodium iodide (I-131) POLATOM is a radioactive iodine capsule used to treat thyroid disorders. Its main therapeutic indications are ablation of residual thyroid tissue after thyroidectomy for differentiated thyroid cancer (papillary and follicular), treatment of metastatic differentiated thyroid cancer, and treatment of hyperthyroidism, including Graves’ disease, toxic multinodular goiter, and toxic adenoma. It is selectively concentrated in thyroid tissue, where beta radiation destroys overactive or malignant thyroid cells.
Iodine-131 has a physical half-life of 8.02 days, meaning the amount of radioactivity in the body approximately halves every 8 days due to physical decay. The biological half-life, which also accounts for iodine excreted in urine and sweat, is shorter than the physical half-life. Most patients reach very low residual activities within 3–6 weeks, and virtually no detectable activity remains after about 80 days. Your team provides you with the specific timeline for your treatment and activity.
Most patients treated with radioactive iodine for differentiated thyroid cancer will need lifelong levothyroxine replacement, since the entire thyroid is deliberately ablated. For Graves’ disease, hypothyroidism develops in approximately 80–90% of patients within the first year after therapy, and lifelong replacement is then required. After treatment of a toxic adenoma or small toxic nodular goiter, the suppressed surrounding thyroid often recovers, and long-term hypothyroidism rates are lower (approximately 10–30%).
Children’s thyroid glands are more sensitive to radiation than adult thyroids, and young children receive a higher dose per unit time than adults during close contact with someone who has been treated with radioactive iodine. To keep their exposure within internationally recommended limits, patients are advised to keep a defined distance from young children, avoid holding them for long periods, and, when possible, arrange alternative childcare for a few days to a few weeks. The exact duration depends on the activity you received and on national regulations.
No. Sodium iodide (I-131) POLATOM is absolutely contraindicated during pregnancy. Iodine-131 crosses the placenta, is concentrated in the fetal thyroid from about 10–12 weeks of gestation onward, and can cause severe or complete destruction of the fetal thyroid gland, resulting in lifelong hypothyroidism and, at high doses, other developmental harm. A pregnancy test is mandatory in women of reproductive potential before treatment. Pregnancy must be avoided for at least 6–12 months after therapy, depending on the indication and administered activity.
The risk of developing a new cancer after therapeutic doses of radioactive iodine is small but not zero. Large epidemiological studies and meta-analyses have shown a modest increase in the long-term risk of secondary malignancies, including leukemia, stomach cancer, bladder cancer, and salivary gland tumors, particularly after repeated high cumulative activities used for metastatic thyroid cancer. For typical single-dose treatment of hyperthyroidism, the excess risk is very small and is generally outweighed by the benefit of controlling thyroid disease, avoiding surgery, and preventing complications of untreated thyrotoxicosis.
Radioactive iodine is a highly effective definitive treatment for Graves’ disease. When an ablative strategy is used (targeting hypothyroidism rather than euthyroidism), a single dose cures hyperthyroidism in approximately 80–90% of patients. Retreatment with a second dose is offered if hyperthyroidism persists or recurs after 6–12 months. Overall, more than 95% of Graves’ disease patients can be cured with one or two doses of I-131. The main trade-off is the very high likelihood of permanent hypothyroidism, which is managed with once-daily levothyroxine for life.
References
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- International Atomic Energy Agency. Nuclear Medicine Resources Manual 2020 Edition. Vienna: IAEA; 2020.
- European Union. Council Directive 2013/59/Euratom laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation. Official Journal of the European Union. 2014;L13/1.
- Sisson JC, Freitas J, McDougall IR, et al. Radiation safety in the treatment of patients with thyroid diseases by radioiodine 131-I: practice recommendations of the American Thyroid Association. Thyroid. 2011;21(4):335–346.
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- World Health Organization. WHO Model List of Essential Medicines – 23rd List. Geneva: WHO; 2023.
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