IOBENGUANE SULFATE I 131
Clinical safety rating: caution
Comprehensive clinical and safety monograph for IOBENGUANE SULFATE I 131 (IOBENGUANE SULFATE I 131).
Iobenguane is a guanethidine analog that is taken up by norepinephrine transporters and accumulates in adrenergic tissues. I-131 emits beta particles and gamma radiation, causing localized cytotoxic effects on cells that take up the compound, particularly neuroendocrine tumors such as pheochromocytoma and paraganglioma.
| Metabolism | Iobenguane is not metabolized; it is primarily excreted unchanged in the urine. A small fraction may be deiodinated by unknown enzymes, releasing free iodide. |
| Excretion | Renal: 40-70% of administered dose excreted unchanged in urine within 24 hours, with complete excretion over several days. Biliary/fecal: less than 2% excreted in feces. |
| Half-life | Terminal elimination half-life: approximately 30-60 hours for the iodide component; the intact iobenguane molecule has a half-life of about 24-48 hours. Clinically, this allows for imaging up to 72 hours post-administration. |
| Protein binding | Approximately 30-45% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Apparent volume of distribution: 2.0-4.0 L/kg, indicating extensive distribution into tissues, especially adrenergic-rich organs like heart, adrenal glands, and tumors. |
| Bioavailability | Intravenous: 100% (only route used clinically). Oral: not applicable; not administered orally due to poor absorption and first-pass metabolism. |
| Onset of Action | Intravenous injection: uptake in target tissues (e.g., neuroendocrine tumors) begins within minutes; scintigraphic images can be obtained as early as 1-4 hours post-injection. |
| Duration of Action | Therapeutic effect (if used for therapy) lasts days to weeks; diagnostic imaging is optimal at 24-48 hours but images can be acquired up to 72-96 hours. Residual radioactivity decays over several days. |
Adults: 185-370 MBq (5-10 mCi) administered intravenously over 1-5 minutes for diagnostic imaging; for therapy, 7.4-11.1 GBq (200-300 mCi) IV over 1-2 hours, repeated every 3-6 months as needed.
| Dosage form | INJECTABLE |
| Renal impairment | GFR <30 mL/min: Contraindicated for therapeutic doses due to increased radiation exposure to kidneys. For diagnostic doses, use with caution and consider dose reduction by 50%. |
| Liver impairment | Child-Pugh Class C: Use contraindicated due to altered biodistribution and increased toxicity. Child-Pugh A or B: No dose adjustment required, but monitor for adverse effects. |
| Pediatric use | Diagnostic: 0.14 mCi/kg (5.18 MBq/kg) IV, minimum 0.5 mCi. Therapeutic: 0.5-1 mCi/kg (18.5-37 MBq/kg) IV, not to exceed adult dose. |
| Geriatric use | Start at lower end of diagnostic dose range (e.g., 5 mCi) and consider dose reduction for therapy (e.g., 150-200 mCi) due to reduced renal function and bone marrow reserve. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for IOBENGUANE SULFATE I 131 (IOBENGUANE SULFATE I 131).
| Breastfeeding | Iobenguane sulfate I 131 is excreted in breast milk. Radioactivity in milk can persist for several days. Breastfeeding should be interrupted and milk discarded for a period determined by the half-life of I-131 (8.02 days) and the administered activity. M/P ratio is not explicitly reported but radioiodine concentrates in mammary tissue. The decision to resume breastfeeding should be based on radiation safety calculations and consultation with a radiation safety officer. |
| Teratogenic Risk | Iobenguane sulfate I 131 is a radioactive diagnostic agent that emits beta and gamma radiation. During pregnancy, exposure to ionizing radiation poses significant fetal risks, particularly during organogenesis (first trimester), with increased risk of fetal malformations, growth restriction, and carcinogenesis. The risk is dose-dependent; radiation doses above 0.1 Gy are associated with adverse outcomes. Use is contraindicated during pregnancy unless potential benefit outweighs risks. |
■ FDA Black Box Warning
WARNING: RADIATION EXPOSURE AND MYELOSUPPRESSION. Iobenguane sulfate I-131 emits radiation. It can cause severe and potentially life-threatening myelosuppression, including neutropenia, thrombocytopenia, and anemia. Patients should have baseline blood counts and monitoring during therapy. Radiation exposure to the patient and healthcare providers must be minimized.
| Serious Effects |
["Hypersensitivity to iobenguane or any component of the formulation","Pregnancy (teratogenic effects)"]
| Precautions | ["Myelosuppression: severe and prolonged; monitor blood counts","Secondary malignancies: due to radiation exposure","MDS/AML: risk of therapy-related myeloid neoplasms","Radiation safety: contamination and exposure precautions","Thyroid uptake: risk of hypothyroidism; administer potassium iodide to block thyroid uptake before administration"] |
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| Fetal Monitoring | Prior to administration, perform a pregnancy test in women of childbearing potential. During therapy, monitor maternal thyroid function as I-131 can accumulate in the thyroid. After administration, fetal radiation exposure should be estimated if inadvertent exposure occurs. No specific fetal monitoring is recommended if contraindicated; if used, consult with radiation safety and obstetrics. |
| Fertility Effects | Iobenguane sulfate I 131 may cause temporary or permanent gonadal damage due to radiation exposure, potentially affecting fertility. The magnitude depends on absorbed dose to the gonads. For usual diagnostic doses (e.g., 20-40 MBq), effects are minimal; higher therapeutic doses pose greater risk. Fertility counseling may be warranted. |