Natriumjodid (I-123) Curiumpharma: Uses, Dosage & Side Effects

What Is Natriumjodid (I-123) Curiumpharma and What Is It Used For?

Natriumjodid (I-123) Curiumpharma contains sodium iodide labeled with the radioactive isotope Iodine-123 (I-123), a cyclotron-produced gamma-emitting radionuclide. This product belongs to the class of radiopharmaceuticals — medications that contain a radioactive substance and are used for either diagnostic imaging or therapeutic purposes in nuclear medicine. In the case of Sodium Iodide I-123, the product is used exclusively for diagnostic purposes, leveraging the thyroid gland's natural ability to concentrate iodine from the bloodstream to produce detailed functional images.

The thyroid gland is unique among organs in its avid uptake of iodine, which it uses as an essential building block for the synthesis of thyroid hormones (thyroxine, T4, and triiodothyronine, T3). The thyroid concentrates iodide from the blood through the sodium-iodide symporter (NIS), a transmembrane glycoprotein located on the basolateral membrane of thyroid follicular cells. This transport mechanism is highly specific and energy-dependent, actively concentrating iodide to levels 20–40 times higher than in the blood plasma. When radioactive Iodine-123 is administered, it follows exactly the same physiological pathway as stable dietary iodine: it is absorbed from the gastrointestinal tract (if given orally) or enters the bloodstream directly (if given intravenously), is actively transported into thyroid cells by the NIS, and is subsequently organified (incorporated into thyroid hormone precursors) within the follicular cells.

Iodine-123 decays by electron capture to Tellurium-123 with a physical half-life of approximately 13.2 hours. The principal gamma photon emission is at 159 keV (abundance approximately 83%), which falls within the optimal energy window for detection by modern gamma cameras equipped with low-energy, high-resolution collimators. This energy level is sufficiently penetrating to exit the body for external detection while being low enough to be efficiently collimated, resulting in high-resolution images with excellent signal-to-noise ratios. The effective half-life of I-123 in the thyroid (accounting for both physical decay and biological clearance) is approximately 7–8 hours, which further reduces the total radiation dose to the patient compared to other radioiodine isotopes.

The primary clinical indications for Sodium Iodide I-123 thyroid imaging include:

• Thyroid scintigraphy (imaging): To evaluate the size, shape, and position of the thyroid gland, detect thyroid nodules and determine whether they are functioning ("hot") or non-functioning ("cold"), identify ectopic thyroid tissue (e.g., sublingual thyroid, struma ovarii), and differentiate between unifocal and multifocal thyroid disease.
• Differential diagnosis of hyperthyroidism: To distinguish between Graves' disease (diffuse increased uptake), toxic multinodular goiter (multiple areas of increased uptake), toxic adenoma (single focal increased uptake with suppression of the remaining gland), and subacute thyroiditis (globally decreased uptake despite clinical hyperthyroidism).
• Radioiodine uptake (RAIU) measurement: To quantify the percentage of administered radioiodine taken up by the thyroid gland at specified time points (typically 4–6 hours and 24 hours), providing a functional assessment of thyroid iodine avidity. This measurement is essential for calculating therapeutic doses of Iodine-131 for patients with hyperthyroidism or thyroid cancer.
• Post-surgical evaluation: To assess residual or recurrent thyroid tissue after thyroidectomy, and to evaluate the success of previous radioiodine ablation therapy in patients with differentiated thyroid carcinoma.
• Congenital hypothyroidism: In neonates and infants, I-123 thyroid imaging can help identify the cause of congenital hypothyroidism, including thyroid agenesis, ectopic thyroid tissue, and dyshormonogenesis.

Compared to the alternative diagnostic radioisotope Technetium-99m pertechnetate (Tc-99m), Iodine-123 offers several specific advantages for thyroid imaging. While Tc-99m pertechnetate is trapped by the NIS similarly to iodide, it is not organified within the thyroid. This means that Tc-99m imaging reflects only the trapping function of the thyroid, whereas I-123 imaging captures both trapping and organification, providing a more complete picture of thyroid function. Additionally, I-123 is more specific for thyroid tissue and produces superior image quality for thyroid scintigraphy. The main advantage of Tc-99m pertechnetate is its wider availability and lower cost, making it an acceptable first-line alternative in settings where I-123 is not readily available.

Curiumpharma, the manufacturer of this product, is a global leader in nuclear medicine and radiopharmaceuticals. The company also produces Natriumjodid (I-131) Curiumpharma, which contains the therapeutic isotope Iodine-131 used for the treatment of hyperthyroidism and differentiated thyroid carcinoma. While both products contain sodium iodide as the pharmaceutical carrier, the different radioactive isotopes (I-123 for diagnosis, I-131 for therapy) give them fundamentally different clinical applications and radiation profiles.

What Should You Know Before Receiving Sodium Iodide I-123?

Contraindications

Sodium Iodide I-123 should not be administered to patients with a known hypersensitivity (allergy) to sodium iodide or any of the excipients in the formulation. While allergic reactions to simple iodide salts are exceedingly rare (and distinct from allergies to iodinated contrast media or iodine-based antiseptics), patients with a documented history of sensitivity should inform their nuclear medicine physician before the procedure.

Pregnancy is a relative contraindication. Radioactive iodine crosses the placenta, and the fetal thyroid begins to accumulate iodine actively from approximately the 10th to 12th week of gestation. Administration of radioactive iodine to a pregnant woman could result in radiation exposure to the fetal thyroid, potentially causing fetal hypothyroidism or thyroid damage. All women of childbearing potential should have a pregnancy test (serum beta-hCG or urine hCG) before the administration of Sodium Iodide I-123. If a thyroid scan is considered clinically essential during pregnancy, the nuclear medicine physician will carefully assess whether the diagnostic benefit justifies the potential risk, and alternative non-radioactive imaging methods (such as ultrasound) should be considered first.

Warnings and Precautions

Before undergoing a thyroid scan with Sodium Iodide I-123, discuss the following with your nuclear medicine physician:

• Kidney function: Since a significant proportion of the administered I-123 is excreted via the kidneys, patients with impaired renal function may have delayed clearance of the radiopharmaceutical, potentially resulting in increased radiation exposure. Adequate hydration and frequent voiding after the procedure are particularly important in these patients to promote urinary excretion.
• Previous iodine exposure: Recent exposure to high levels of iodine (from iodinated contrast media used in CT scans, iodine-containing medications like amiodarone, dietary iodine supplements, or topical iodine antiseptics) can saturate the thyroid's iodine uptake mechanism and significantly reduce the uptake of I-123, leading to suboptimal imaging or falsely low uptake measurements. Your physician will inquire about any recent iodine exposure and may recommend postponing the procedure.
• Thyroid medication status: Thyroid hormones and anti-thyroid medications directly affect the thyroid's iodine uptake and must be discontinued before the procedure according to specific timelines (see Drug Interactions section below).
• Allergy history: While allergic reactions to sodium iodide are extremely rare at the trace amounts used in diagnostic nuclear medicine, inform your physician of any known allergies, particularly to iodine-containing substances.

Children and Adolescents

Sodium Iodide I-123 can be used in pediatric patients, including neonates, when clinically indicated. In fact, I-123 thyroid scintigraphy is the recommended imaging modality for the evaluation of congenital hypothyroidism in newborns, as it can identify thyroid agenesis, ectopic thyroid tissue, and dyshormonogenesis. The administered activity is adjusted for the child's body weight or body surface area according to the pediatric dosimetry recommendations of the EANM Dosimetry Committee. Children are more radiosensitive than adults, and the long-term radiation risk per unit dose is higher in younger patients due to their greater life expectancy and more rapidly dividing cells. Therefore, the administered activity should be the minimum necessary to achieve adequate diagnostic image quality, following the ALARA (As Low As Reasonably Achievable) principle.

Pregnancy and Breastfeeding

As noted above, Sodium Iodide I-123 is generally contraindicated during pregnancy. If a nuclear medicine procedure using radioactive iodine is considered clinically essential in a pregnant woman, the nuclear medicine physician must carefully weigh the expected diagnostic benefit against the potential radiation risk to the fetus. The radiation dose to the fetal thyroid from diagnostic I-123 studies is substantially lower than from I-131 studies, but it is not negligible, particularly after the 12th week of gestation when the fetal thyroid becomes functionally active. Alternative diagnostic approaches, including thyroid ultrasound and serum thyroid function tests, should be used preferentially in pregnant women whenever possible.

If a woman has received Sodium Iodide I-123 and is breastfeeding, breastfeeding should be interrupted. The European Association of Nuclear Medicine (EANM) recommends that breastfeeding be discontinued for at least 3 days after administration of I-123 sodium iodide, as radioactive iodine is secreted in breast milk and could be ingested by the nursing infant, potentially exposing the infant's thyroid to radiation. Breast milk expressed during this period should be discarded. The mother should be encouraged to express and discard milk regularly during the interruption period to maintain lactation if she wishes to resume breastfeeding afterward.

Effects on Fertility and Driving

No effects on fertility are expected from the low radiation doses associated with diagnostic use of Sodium Iodide I-123. The gonadal radiation dose from a typical diagnostic thyroid scan is very low and well below the thresholds associated with adverse effects on fertility or hereditary risks. Similarly, Sodium Iodide I-123 at diagnostic doses is not expected to affect the ability to drive or operate machinery, as the radiopharmaceutical itself has no pharmacological effects at the trace amounts administered.

How Does Sodium Iodide I-123 Interact with Other Drugs?

Unlike conventional pharmaceutical drug interactions that involve pharmacokinetic or pharmacodynamic mechanisms, the interactions relevant to Sodium Iodide I-123 primarily concern the effects of medications and dietary substances on thyroid iodine uptake. These interactions can result in falsely elevated or falsely decreased radioiodine uptake values and can compromise the diagnostic quality of thyroid scintigraphy. Therefore, it is essential that the nuclear medicine physician obtains a comprehensive medication history before scheduling and performing a thyroid scan.

The following categories of medications and substances are known to interfere with thyroid iodine uptake:

Thyroid hormone replacement therapy (levothyroxine, liothyronine) suppresses thyroid-stimulating hormone (TSH) from the pituitary gland. Since TSH is the primary driver of thyroid iodine uptake via the NIS, suppressed TSH levels result in decreased radioiodine uptake and potentially false-negative scintigraphic findings. Levothyroxine has a long half-life of approximately 7 days, requiring a withdrawal period of 4–6 weeks to allow TSH to rise to levels that will stimulate adequate iodine uptake. Liothyronine has a shorter half-life of approximately 1 day, requiring only 10–14 days of withdrawal. In some clinical situations, patients can be switched from levothyroxine to liothyronine for 4 weeks, followed by 2 weeks of liothyronine withdrawal, to minimize the total period of hypothyroidism before the scan.

Anti-thyroid medications (thionamides) such as methimazole, carbimazole, and propylthiouracil inhibit thyroid hormone synthesis by blocking the organification of iodine within the thyroid gland. While they do not directly block iodine trapping by the NIS, their inhibition of organification and the consequent rise in TSH can paradoxically increase radioiodine uptake. However, they can also affect the interthyroidal distribution of iodine and the quality of scintigraphic images. A short withdrawal period of 2–5 days is generally recommended.

Amiodarone presents a particularly challenging interaction because of its extremely high iodine content (approximately 37% by weight, releasing approximately 6 mg of free iodine per 200 mg tablet daily) and its very long tissue half-life of 40–55 days (with a terminal elimination half-life of up to 100 days in some patients). Even after discontinuation, significant iodine stores may persist in adipose tissue and other organs for months, continuing to suppress thyroid radioiodine uptake. In patients taking long-term amiodarone, thyroid scintigraphy with I-123 may not be feasible, and alternative diagnostic strategies (such as thyroid ultrasound with Doppler flow studies, serum thyroid function tests, or Tc-99m MIBI imaging) may need to be considered.

What Is the Correct Dosage of Sodium Iodide I-123?

Sodium Iodide I-123 must always be administered under the supervision of a qualified nuclear medicine physician in a licensed nuclear medicine facility. The dose (expressed in megabecquerels, MBq, or millicuries, mCi) is individually determined based on the clinical indication, the patient's body weight and thyroid function, and the performance characteristics of the imaging equipment. The objective is to administer the minimum activity necessary to obtain adequate diagnostic information, consistent with the ALARA (As Low As Reasonably Achievable) principle of radiation protection.

Adults

The product is supplied as a solution with a radioactive concentration of 37 MBq/mL at the reference date and time. The activity at the time of administration must be measured using an appropriately calibrated dose calibrator (radionuclide activity meter) and adjusted for radioactive decay from the reference time using standard decay tables or calculations. The nuclear medicine technologist or physician will draw up the required volume to deliver the prescribed activity at the time of administration.

Children

Pediatric doses of Sodium Iodide I-123 are calculated based on the child's body weight or body surface area, using the fraction-of-adult-dose method recommended by the EANM Pediatric Dosimetry Committee. The minimum recommended activity that should yield adequate diagnostic image quality in pediatric patients is typically around 1–3 MBq. For neonatal thyroid imaging (e.g., evaluation of congenital hypothyroidism), the recommended activity is approximately 1–3.7 MBq, though this may vary based on institutional protocols and equipment sensitivity. The EANM pediatric dosage card provides specific multiplication factors based on body weight ranging from 3 kg to 68 kg.

Elderly

No specific dose adjustment is required for elderly patients. However, renal function should be assessed, as age-related decline in glomerular filtration rate may result in slower clearance of unbound radioiodide from the body, potentially increasing the overall radiation dose. Adequate hydration should be ensured, and the patient should be encouraged to void frequently after the procedure to promote urinary excretion of the radiopharmaceutical.

Administration Procedure

Sodium Iodide I-123 can be administered either orally or intravenously. For oral administration, the measured dose may be given in a small volume of liquid or as a prepared capsule. For intravenous administration, the solution is injected as a slow bolus or short infusion. The choice of route depends on the clinical indication and institutional practice. Oral administration is more commonly used for routine thyroid uptake studies and scintigraphy, while intravenous administration provides more precise control over the administered activity and timing.

Imaging is typically performed at specific time points after administration:

• 4–6 hours post-administration: Initial uptake images; this timing captures the early uptake phase and may be sufficient for many clinical indications.
• 24 hours post-administration: Delayed images; these capture the maximum thyroid uptake and are essential for accurate RAIU measurement and for detecting some thyroid abnormalities.
• Additional time points: In certain clinical situations (e.g., suspected ectopic thyroid tissue, whole-body imaging for metastatic thyroid carcinoma), additional imaging at earlier or later time points may be performed.

Overdose

In the unlikely event of a radiation overdose due to accidental administration of an excessively high activity of Sodium Iodide I-123, the absorbed dose to the patient should be estimated and documented. The primary measures to reduce the radiation dose are to promote rapid renal excretion through vigorous hydration and frequent voiding, and to administer potassium perchlorate (if available and appropriate) to block further thyroid uptake of radioiodide. Thyroid-blocking agents such as stable (non-radioactive) potassium iodide can also be administered within the first few hours to competitively inhibit further uptake. Given the 13.2-hour physical half-life of I-123, the radiation exposure will decrease relatively rapidly through natural decay.

What Are the Side Effects of Sodium Iodide I-123?

Sodium Iodide I-123 is administered in extremely small chemical quantities (trace amounts) for diagnostic purposes. At these microgram or nanogram quantities, sodium iodide has no pharmacological effects on the body and does not cause the side effects that would be associated with pharmacological doses of iodine. The safety considerations for this radiopharmaceutical relate primarily to the radiation exposure it delivers, rather than to any chemical toxicity.

Adverse reactions to diagnostic doses of Sodium Iodide I-123 are exceedingly rare and have been documented in the medical literature primarily as isolated case reports rather than systematic findings from clinical trials. The following frequency classification is based on available pharmacovigilance data and post-marketing surveillance:

The principal safety consideration with any radiopharmaceutical is the radiation dose delivered to the patient and the associated theoretical risk of stochastic effects (primarily radiation-induced cancer). The radiation dosimetry for Sodium Iodide I-123 is well characterized. For a standard adult thyroid scintigraphy study using 14.8 MBq (0.4 mCi), the estimated absorbed dose to the thyroid is approximately 15–25 mGy (depending on thyroid uptake), and the effective dose to the whole body is approximately 2–4 mSv. For context, this is comparable to the radiation dose from a standard chest CT scan and represents a small fraction of the annual background radiation exposure in most geographic regions.

The radiation dose from I-123 is substantially lower than that from equivalent diagnostic studies using I-131. For the same diagnostic information, the thyroid absorbed dose from I-123 is approximately 1/100th of the dose from I-131, which is a major reason why I-123 is the preferred diagnostic radioiodine isotope. The absence of beta particle emissions from I-123 (as opposed to the high-energy beta emissions from I-131) is the primary factor responsible for this dramatically reduced thyroid dose.

Stochastic radiation effects (cancer induction) follow a linear no-threshold model in radiation protection practice, meaning that any radiation dose, no matter how small, carries a theoretical non-zero risk. However, at the low doses associated with diagnostic nuclear medicine studies, this risk is extremely small and is estimated at approximately 0.01–0.02% per 10 mSv of effective dose. For a typical I-123 thyroid scan delivering 2–4 mSv, the estimated additional lifetime cancer risk is in the range of 0.002–0.008% — far lower than the baseline lifetime cancer risk of approximately 25–40%.

Special attention should be given to the radiation dose in pediatric patients, who are more radiosensitive than adults. The higher radiosensitivity of pediatric tissue, combined with the longer expected lifespan over which radiation effects could manifest, means that the risk per unit dose is greater in children. This underscores the importance of administering the minimum diagnostic activity and using the EANM pediatric dosimetry recommendations for dose calculation.

How Should Sodium Iodide I-123 Be Stored?

Sodium Iodide I-123, as a radiopharmaceutical, is subject to strict storage and handling requirements that go beyond those of conventional pharmaceuticals. These requirements are governed by both pharmaceutical Good Manufacturing Practice (GMP) standards and national radiation protection regulations. Patients do not need to store or handle this product, as it is maintained entirely within the nuclear medicine department's radiopharmacy and is prepared for administration by qualified personnel.

The following storage and handling requirements apply to the nuclear medicine facility:

• Temperature: Store at the temperature specified on the product label, typically at 15–25 °C (room temperature) or 2–8 °C (refrigerated), depending on the specific formulation and manufacturer's instructions. Do not freeze.
• Radiation shielding: The product must be stored in appropriate lead or tungsten shielding containers to minimize radiation exposure to personnel. The primary gamma energy of I-123 (159 keV) is effectively attenuated by lead shielding of approximately 1–2 mm thickness.
• Designated storage area: Store in a designated radioactive materials storage area with restricted access, appropriate signage, and radiation monitoring, in compliance with local radiation protection regulations.
• Shelf life and radioactive decay: Due to the relatively short physical half-life of I-123 (13.2 hours), the product has a limited shelf life from the time of calibration. The usable period is determined by the radioactive concentration at the time of intended use, taking into account the decay from the reference date and time stated on the label. Typically, the product is used within 24–48 hours of the calibration date.
• Visual inspection: Before use, visually inspect the solution. It should be clear and colorless. Do not use if the solution is discolored, contains particulate matter, or if the container shows signs of damage or tampering.
• Disposal: Any unused product, expired material, or contaminated waste must be disposed of in accordance with national regulations for radioactive waste. Due to the short half-life of I-123, waste can often be stored for decay (approximately 10 half-lives, or roughly 5.5 days) before disposal as non-radioactive pharmaceutical waste, subject to local regulatory requirements.

The nuclear medicine facility maintains comprehensive records of the receipt, storage, dispensing, administration, and disposal of all radioactive materials, including Sodium Iodide I-123, as required by national radiation protection authorities. These records include the product identity, batch number, calibration activity and date, activity administered to each patient, and disposal records for any unused material.

What Does Sodium Iodide I-123 Contain?

Understanding the composition of Sodium Iodide I-123 is important for nuclear medicine professionals responsible for its preparation and administration, and for patients who may have specific sensitivities to pharmaceutical excipients.

Active Substance

The active substance is sodium iodide [¹²³I] (sodium iodide labeled with Iodine-123). Iodine-123 is produced in a cyclotron by proton irradiation of enriched Xenon-124 gas or Tellurium-123 targets, followed by radiochemical processing to obtain carrier-free or no-carrier-added sodium iodide [¹²³I] in solution. The radioactive concentration at the reference date and time is 37 MBq/mL. The specific activity is very high, meaning that the chemical mass of iodide in the product is extremely small (in the nanogram to microgram range), which is far below any pharmacologically active threshold.

Excipients

Radionuclidic Purity

The radionuclidic purity of Sodium Iodide I-123 is an important quality parameter. The European Pharmacopoeia specifies that I-123 preparations must contain not less than 99.9% of total radioactivity as I-123, with strictly controlled limits on radionuclidic impurities, particularly Iodine-125 (which has a longer half-life of 59.4 days and would increase the radiation dose) and Iodine-124 (half-life 4.2 days). These impurities arise from competing nuclear reactions during cyclotron production and are minimized by optimized irradiation parameters and radiochemical purification processes. Quality control testing is performed by the manufacturer and/or the nuclear medicine facility before patient administration.

Packaging and Presentation

Sodium Iodide I-123 is typically supplied in a multi-dose glass vial sealed with a rubber stopper and aluminum crimp seal, contained within a lead or tungsten shielding pot. The vial label states the product name, batch number, calibration activity and date/time, radioactive concentration, volume, expiration date, and storage conditions. The outer shielding container bears appropriate radioactive material transport labels in accordance with international transport regulations (IAEA Transport Regulations, ADR/RID for road/rail transport).