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

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

MIBG (I-123) Curiumpharma contains iobenguane, also known as meta-iodobenzylguanidine (MIBG), labeled with the radioactive isotope iodine-123 (123I). Iobenguane is a synthetic compound that is structurally related to both norepinephrine (noradrenaline), the primary neurotransmitter of the sympathetic nervous system, and guanethidine, an antihypertensive agent. This dual structural resemblance gives MIBG its unique ability to be actively taken up, stored, and retained by cells that possess the norepinephrine transporter (NET) and intracellular catecholamine storage vesicles. These properties make it an ideal tracer for imaging tissues that are rich in sympathetic nerve terminals or that are derived from the neural crest, including many neuroendocrine tumors.

The development of MIBG as a diagnostic radiopharmaceutical dates back to the late 1970s and early 1980s, when researchers at the University of Michigan, led by Dr. James Sisson and Dr. Donald Wieland, first synthesized radioiodinated MIBG and demonstrated its selective accumulation in the adrenal medulla. The initial clinical application was the detection of pheochromocytoma, a catecholamine-secreting tumor of the adrenal gland. Since then, the clinical indications for MIBG scintigraphy have expanded considerably, and the agent is now a well-established and widely used tool in nuclear medicine departments worldwide.

The mechanism of MIBG uptake involves two principal pathways. The primary uptake mechanism, known as uptake-1, is an active, energy-dependent, sodium- and temperature-dependent process mediated by the norepinephrine transporter (NET) located on the cell membrane of sympathetic nerve terminals and neuroendocrine cells. This is the same transporter responsible for the reuptake of norepinephrine from the synaptic cleft under physiological conditions. After entering the cell via NET, MIBG is transported into intracellular storage granules (chromaffin granules) by the vesicular monoamine transporter (VMAT), where it remains concentrated. A secondary, non-specific uptake mechanism (uptake-2) also exists, which is passive diffusion across the cell membrane. However, uptake-1 accounts for the majority of specific MIBG accumulation in target tissues and is the basis for its diagnostic utility.

Iodine-123 is the preferred radiolabel for diagnostic MIBG scintigraphy because it emits gamma photons at an energy of 159 keV, which is optimal for detection by modern gamma cameras and SPECT (Single Photon Emission Computed Tomography) systems. Additionally, iodine-123 has a physical half-life of 13.2 hours, which is long enough to allow imaging at both early (4 hours) and delayed (24 hours) time points, but short enough to limit the total radiation dose to the patient. Compared to iodine-131 (which has a half-life of 8 days and emits high-energy beta particles in addition to gamma photons), iodine-123 delivers significantly less radiation dose and produces superior image quality, making it the preferred isotope for diagnostic purposes. Iodine-131-labeled MIBG is reserved primarily for therapeutic applications (radionuclide therapy) in inoperable or metastatic neuroendocrine tumors.

Primary Clinical Indications

MIBG (I-123) scintigraphy is indicated for several distinct clinical applications, each leveraging the agent's selective uptake in sympathetically innervated tissues:

• Pheochromocytoma and paraganglioma: MIBG scintigraphy is considered a cornerstone in the localization and functional characterization of pheochromocytomas (tumors arising from the chromaffin cells of the adrenal medulla) and paragangliomas (extra-adrenal tumors arising from sympathetic and parasympathetic paraganglia). It is particularly valuable for detecting multifocal disease, extra-adrenal tumors, and metastatic disease that may not be apparent on anatomical imaging (CT or MRI) alone. The sensitivity of 123I-MIBG scintigraphy for sporadic pheochromocytoma is approximately 85–95%, with specificity exceeding 95%.
• Neuroblastoma: Neuroblastoma is one of the most common solid tumors of childhood, originating from neural crest-derived cells. MIBG scintigraphy plays a critical role in the initial diagnosis, staging, treatment response assessment, and post-treatment surveillance of neuroblastoma. Approximately 90% of neuroblastomas demonstrate MIBG avidity. The International Neuroblastoma Risk Group (INRG) staging system incorporates MIBG scan findings as a key component. MIBG scintigraphy can detect primary tumors, lymph node involvement, bone and bone marrow metastases, and soft tissue deposits with high sensitivity.
• Other neuroendocrine tumors: MIBG scintigraphy can also be used in the evaluation of carcinoid tumors, medullary thyroid carcinoma, ganglioneuromas, and other tumors of neural crest origin. However, sensitivity varies among tumor types, and alternative imaging modalities (such as 68Ga-DOTATATE PET/CT for somatostatin receptor-expressing tumors) may be preferred in certain clinical scenarios.
• Cardiac sympathetic innervation imaging: 123I-MIBG cardiac scintigraphy has emerged as an important prognostic tool in patients with heart failure. By measuring the heart-to-mediastinum (H/M) ratio of MIBG uptake on early and delayed images, clinicians can assess the integrity and function of cardiac sympathetic innervation. Reduced cardiac MIBG uptake (low H/M ratio) correlates with increased risk of cardiac events, arrhythmias, and mortality, and can aid in patient selection for implantable cardioverter-defibrillator (ICD) therapy and cardiac resynchronization therapy (CRT). The ADMIRE-HF (AdreView Myocardial Imaging for Risk Evaluation in Heart Failure) trial demonstrated that a late H/M ratio below 1.6 identified heart failure patients at significantly higher risk of adverse cardiac outcomes.

What Should You Know Before Receiving MIBG (I-123) Curiumpharma?

Contraindications

MIBG (I-123) Curiumpharma is contraindicated in patients with known hypersensitivity to iobenguane (meta-iodobenzylguanidine) or to any of the excipients in the formulation. Individuals with a documented allergy to iodine or iodine-containing substances should not receive this product. While true iodine allergy is extremely rare and often confused with allergy to iodinated contrast agents (which have a different mechanism), any history of adverse reactions to iodine-containing products should be discussed with the nuclear medicine physician before the procedure.

There are no absolute contraindications based on organ function, as MIBG (I-123) is a diagnostic tracer administered in sub-pharmacological quantities. However, the radiation exposure from the procedure constitutes a relative contraindication during pregnancy, and the decision to perform the scan must be based on a careful risk-benefit analysis in any situation where the patient may be pregnant.

Thyroid Blockade (Mandatory)

The rationale for thyroid blockade is well established in nuclear medicine practice. After intravenous administration, a proportion of the iodine-123 label may become detached from the iobenguane molecule through deiodination. This free radioiodine would naturally be trapped by the thyroid gland via the sodium-iodide symporter (NIS), leading to unwanted thyroid irradiation. By saturating the thyroid with non-radioactive stable iodine before and after the scan, free radioiodine uptake is competitively inhibited, reducing the thyroid absorbed dose by more than 90%.

The standard thyroid blockade protocol for adults involves administration of potassium iodide (typically 130 mg) orally, beginning at least 1 hour before the MIBG injection and continuing for 1–2 days post-injection. For pediatric patients, the dose is adjusted according to age and body weight. Alternative agents such as Lugol's solution or potassium perchlorate (200–400 mg) may be used when potassium iodide is not available or is contraindicated. The European Association of Nuclear Medicine (EANM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI) both provide detailed guidance on thyroid blockade protocols in their respective MIBG procedural guidelines.

Warnings and Precautions

MIBG (I-123) Curiumpharma must only be used in authorized nuclear medicine facilities by healthcare professionals who are qualified and experienced in the safe handling and administration of radiopharmaceuticals. The product involves ionizing radiation, and all relevant radiation protection regulations and institutional protocols must be followed to minimize exposure to the patient, healthcare workers, and the general public.

• Radiation exposure: As with all nuclear medicine procedures, the benefit of the diagnostic information obtained must be weighed against the radiation dose to the patient. The effective dose from a standard 123I-MIBG diagnostic scan in adults is approximately 4–5 mSv, which is comparable to approximately 1.5–2 years of natural background radiation. In pediatric patients, the radiation dose is adjusted by using weight-based activity calculations according to the EANM/SNMMI pediatric dosage card, but children are inherently more radiosensitive than adults, requiring particular attention to dose optimization.
• Patient hydration: Adequate hydration before and after the procedure is recommended to promote urinary excretion of the radiopharmaceutical and thereby reduce radiation dose to the bladder and other non-target organs. Patients should be encouraged to void frequently during the 24-hour imaging period.
• Slow injection: MIBG (I-123) should be administered by slow intravenous injection over 1–5 minutes (or by infusion over up to 30 minutes in some protocols) to minimize the risk of transient hemodynamic effects. Rapid injection may cause a brief rise in blood pressure due to the structural similarity of MIBG to norepinephrine. This is particularly relevant in patients with pheochromocytoma, where the catecholamine-secreting tumor may amplify the hemodynamic response. Blood pressure and heart rate should be monitored during and immediately after the injection in patients with known or suspected pheochromocytoma.
• Renal impairment: The majority of MIBG (I-123) is excreted via the kidneys. In patients with renal impairment, excretion may be delayed, potentially resulting in higher radiation exposure. Clinical judgment should guide the use of MIBG scintigraphy in patients with significant renal dysfunction, and additional hydration measures may be warranted.

Pregnancy and Breastfeeding

MIBG (I-123) Curiumpharma should not be administered to pregnant women unless the expected diagnostic benefit is considered to clearly outweigh the potential risk to the fetus. All radiopharmaceutical procedures involve exposure of the fetus to ionizing radiation, and iodine-123 crosses the placenta. The fetal thyroid begins to concentrate iodine from approximately the 12th week of gestation, making the second and third trimesters periods of particular concern for fetal thyroid irradiation. If an MIBG scan is deemed clinically essential during pregnancy, the lowest diagnostic activity should be used, and thyroid blockade of the mother should be ensured.

For women who are breastfeeding, the European Association of Nuclear Medicine recommends interrupting breastfeeding for at least 3 days after the administration of 123I-MIBG. Free radioiodine and iobenguane may be excreted in breast milk, and an infant ingesting this milk would receive an unnecessary radiation dose. During the interruption period, breast milk should be expressed and discarded. Breastfeeding can be resumed after the recommended interval has elapsed and once radiation safety monitoring confirms acceptable levels.

Women of childbearing potential should undergo a pregnancy test before the procedure if there is any possibility of pregnancy. The nuclear medicine team should be informed of any possibility of pregnancy, missed menstrual periods, or current breastfeeding before the appointment.

Use in Children

MIBG (I-123) scintigraphy is widely used in pediatric nuclear medicine, with neuroblastoma being the most common indication in children. The administered activity is calculated according to the child's body weight using the EANM/SNMMI pediatric dosage card, which ensures that the minimum effective activity is used to obtain diagnostic-quality images while minimizing radiation exposure. Children are more radiosensitive than adults, and adherence to the ALARA (As Low As Reasonably Achievable) principle is particularly important. Age-appropriate thyroid blockade with potassium iodide is mandatory, and sedation or immobilization techniques may be required for young children who cannot remain still during the imaging sessions.

How Does MIBG (I-123) Interact with Other Drugs?

Drug interactions with MIBG (I-123) are critically important in clinical practice because they can profoundly affect the diagnostic accuracy of the scan. Unlike pharmacokinetic drug interactions that alter absorption, metabolism, or excretion of a drug, MIBG interactions are primarily pharmacodynamic in nature: interfering medications either compete with MIBG for uptake via the norepinephrine transporter (NET), inhibit the vesicular storage of MIBG in chromaffin granules, or deplete norepinephrine stores from sympathetic nerve terminals. Any of these mechanisms can reduce MIBG uptake in target tissues, leading to false-negative results that may cause a tumor to be missed or cardiac innervation to be underestimated.

The clinical significance of these interactions cannot be overstated. A false-negative MIBG scan due to unrecognized medication interference can delay the diagnosis of a potentially life-threatening tumor such as pheochromocytoma, lead to understaging of neuroblastoma, or provide inaccurate prognostic information in heart failure assessment. Therefore, a thorough medication review by the nuclear medicine team is an essential step in the preparation for MIBG scintigraphy.

The following table summarizes the major drug categories known to interfere with MIBG uptake and the recommended withdrawal periods before the scan:

It is essential to note that the decision to discontinue any medication must be made in consultation with the prescribing physician, as abrupt withdrawal of certain medications (particularly antidepressants and antihypertensives) can carry significant clinical risks. In some cases, the nuclear medicine physician may elect to proceed with the scan despite concurrent medication use, accepting the possibility of reduced sensitivity, particularly when the clinical urgency of the scan outweighs the risks of medication discontinuation.

Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, sertraline, and citalopram have historically been listed as potentially interfering agents. However, more recent evidence suggests that SSRIs at standard therapeutic doses do not significantly affect MIBG uptake via NET, and current EANM guidelines do not mandate their discontinuation before MIBG scintigraphy. Nevertheless, individual institutional protocols may vary, and patients should always disclose all SSRI use to their nuclear medicine team.

What Is the Correct Dosage of MIBG (I-123) Curiumpharma?

MIBG (I-123) Curiumpharma is supplied as a solution for injection at a concentration of 74 MBq/ml at the time of calibration. The product is intended solely for intravenous administration in nuclear medicine departments by trained healthcare professionals. Unlike conventional oral or self-injectable medications, patients do not handle, prepare, or administer this radiopharmaceutical themselves. All aspects of dosing, preparation, and injection are under the control of the nuclear medicine team.

Adults

The recommended administered activity for adults varies depending on the clinical indication:

The injection should be administered slowly over 1–5 minutes via a secure intravenous line. Some institutions prefer an infusion over 15–30 minutes, diluted in 0.9% sodium chloride, particularly in patients with known or suspected pheochromocytoma, to minimize the risk of transient hemodynamic changes. The injection should be through a well-placed intravenous cannula to avoid extravasation (leakage of the radioactive solution into the surrounding tissue), which would both compromise image quality and deliver an unnecessary localized radiation dose.

After injection, the patient should remain well hydrated and void frequently to promote renal excretion of the tracer and reduce bladder radiation dose. The patient typically returns for imaging at two time points: early imaging at approximately 4 hours post-injection and delayed imaging at approximately 24 hours post-injection. Each imaging session typically lasts 30–60 minutes, depending on whether planar-only or combined planar/SPECT (or SPECT/CT) imaging is performed.

Children

Pediatric MIBG scintigraphy requires special consideration. Young children who cannot cooperate with the scanning process may require sedation or general anesthesia to prevent motion artifacts during imaging. Age-appropriate thyroid blockade is mandatory. The imaging protocol in children is similar to adults (early and delayed imaging), although some centers may adapt the timing based on the child's clinical condition and logistical considerations.

Elderly Patients

No specific dose adjustment is required for elderly patients. The standard adult activity range applies. However, clinicians should be aware that renal function may be reduced in elderly patients, potentially leading to slower excretion and modestly higher radiation exposure. Adequate hydration is particularly important in this population. Additionally, cardiac MIBG imaging interpretation in elderly patients should account for the normal age-related decline in cardiac sympathetic innervation, which may result in lower heart-to-mediastinum ratios compared to younger adults.

Missed Dose

The concept of a missed dose does not apply to MIBG (I-123) in the same way as for conventional medications, as it is a single-administration diagnostic procedure. If a scheduled MIBG scan is cancelled or postponed, the nuclear medicine team will arrange a new appointment. Since the radioactive isotope decays with a 13.2-hour half-life, a prepared dose cannot simply be stored for later use beyond its calibration window, and a fresh preparation may be required for the rescheduled scan.

Overdose

Accidental administration of a higher-than-intended activity of MIBG (I-123) would result in a proportionally higher radiation dose to the patient. In such a scenario, the nuclear medicine physician should assess the excess dose and calculate the additional radiation exposure. The primary risk is radiation-related rather than pharmacological, as MIBG is administered in sub-pharmacological quantities that are unlikely to produce significant pharmacological effects. Encouraging the patient to hydrate vigorously and void frequently would help accelerate urinary excretion and reduce the radiation burden to the bladder and kidneys. The incident should be documented and reported according to institutional radiation safety policies.

What Are the Side Effects of MIBG (I-123) Curiumpharma?

MIBG (I-123) Curiumpharma is administered as a single diagnostic dose in sub-pharmacological quantities. Because the mass of iobenguane injected is extremely small (typically in the microgram range), significant systemic pharmacological effects are not expected. However, adverse reactions can occur, ranging from minor injection-related effects to rare systemic reactions. The overall incidence of adverse events with 123I-MIBG is low, and the vast majority of patients undergo the procedure without any adverse effects.

The following frequency-based classification of adverse effects is based on post-marketing surveillance data, published literature, and EANM/SNMMI reporting. Frequency categories follow the standard convention: very common (≥1/10), common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), rare (<1/1,000), and not known (frequency cannot be estimated from available data).

Radiation-Related Risks

As with all procedures involving ionizing radiation, there is a small stochastic (probability-based) risk of long-term effects, including the theoretical risk of radiation-induced malignancy. However, for diagnostic nuclear medicine procedures at the activity levels used for 123I-MIBG scintigraphy, this risk is extremely small and is considered to be far outweighed by the diagnostic benefit of the procedure in the context of the clinical indication.

The effective dose from a typical adult 123I-MIBG diagnostic scan (370 MBq) is approximately 4.8 mSv. To put this in perspective, the average annual background radiation dose from natural sources in many countries is approximately 2–3 mSv, and a standard chest CT scan delivers approximately 5–7 mSv. The organs receiving the highest absorbed dose from 123I-MIBG are the liver (approximately 0.05 mGy/MBq), the urinary bladder wall (approximately 0.05 mGy/MBq), and the adrenal glands. In patients with pheochromocytoma or other MIBG-avid tumors, the tumor itself may receive a higher localized dose due to concentrated uptake.

Reporting Side Effects

If you experience any side effects during or after the MIBG scan, inform the nuclear medicine staff immediately. Any unexpected adverse reactions should be reported by the healthcare team to the relevant national pharmacovigilance authority (e.g., the EMA in Europe, the FDA in the United States, or the MHRA in the United Kingdom) as part of post-marketing surveillance. Reporting of adverse events contributes to the ongoing safety monitoring of radiopharmaceutical products.

How Should MIBG (I-123) Curiumpharma Be Stored?

MIBG (I-123) Curiumpharma is a radiopharmaceutical that is manufactured, distributed, stored, and administered exclusively within the controlled environment of licensed nuclear medicine departments and radiopharmacies. Patients and members of the general public do not purchase, store, or handle this product at any point. All storage and handling are the responsibility of qualified nuclear medicine professionals who are trained in radiation safety and radioactive materials management.

The product should be stored in its original lead-shielded container (pig) at a temperature of 15–25 °C (59–77 °F), protected from light. It should not be frozen. Due to the short physical half-life of iodine-123 (13.2 hours), the shelf life of the prepared product is inherently limited. The product must be used within the timeframe specified on the label, which is determined by the radioactive decay characteristics and the radiochemical stability of the iobenguane-123I complex. Typically, the product should be used within 8–24 hours of calibration, depending on the manufacturer's specifications.

After the expiration time, any unused product must be disposed of in accordance with national and institutional regulations for radioactive waste. Short-lived radioactive waste from iodine-123 is typically held for decay in shielded storage until the activity falls below the relevant clearance levels, after which it can be disposed of as non-radioactive pharmaceutical waste. All disposal must comply with the relevant national regulatory framework governing the management of radioactive materials.

The product should be visually inspected before use. The solution should be clear and colorless to slightly yellow. Do not use the product if it appears cloudy, discolored, or contains particulate matter, or if the container is damaged or the integrity of the closure has been compromised.

What Does MIBG (I-123) Curiumpharma Contain?

MIBG (I-123) Curiumpharma is supplied as a sterile, pyrogen-free solution for intravenous injection. Each milliliter of solution contains 74 MBq of iobenguane (123I) at the date and time of calibration. The radioactive concentration decreases over time as the iodine-123 decays, following the standard radioactive decay equation. The actual activity at the time of use must be calculated by the radiopharmacist using the calibration data provided on the product label and the known half-life of 13.2 hours.

Active Substance

The active substance is iobenguane (meta-iodobenzylguanidine, MIBG) labeled with iodine-123 (123I). Iobenguane is a synthetic guanidine analogue with the chemical name meta-iodobenzylguanidine. The molecular formula of iobenguane is C₈H₁₀IN₃, and when the iodine atom is the radioactive isotope 123I, the compound becomes a radiopharmaceutical suitable for gamma camera imaging and SPECT. The specific activity (radioactivity per unit mass) is high, meaning that the mass of iobenguane administered is extremely small (typically in the microgram range), far below any pharmacologically active dose.

Excipients

The formulation contains the following excipients, which serve to maintain the chemical and radiochemical stability of the product:

• Sodium dihydrogen phosphate / disodium hydrogen phosphate: Buffer system to maintain the pH of the solution within an appropriate range (typically pH 4.0–7.0) for intravenous injection.
• Ascorbic acid (vitamin C): Included as a stabilizer to prevent radiolytic degradation of the iobenguane-123I bond. Ionizing radiation from the radionuclide can generate free radicals in the solution that could break the carbon-iodine bond, releasing free radioiodine and reducing the radiochemical purity of the product. Ascorbic acid acts as a free radical scavenger, preserving radiochemical integrity throughout the shelf life.
• Water for injections: Solvent, meeting pharmacopoeial standards for parenteral preparations.
• Sodium chloride: May be present to adjust tonicity.

The product does not contain any preservatives. It is intended for single use only, and any unused portion remaining after the dose has been drawn should be disposed of in accordance with institutional protocols for radioactive waste.

Physical Properties of Iodine-123

Iodine-123 is a cyclotron-produced radionuclide with the following physical characteristics:

The 159 keV gamma photon energy of iodine-123 is well matched to the sensitivity peak of sodium iodide (NaI) scintillation detectors used in gamma cameras, resulting in excellent imaging characteristics. The absence of high-energy beta emissions (unlike iodine-131) means that the radiation dose to the patient is significantly lower, making iodine-123 the preferred isotope for diagnostic MIBG imaging.