Iodine I 131 metaiodobenzylguanidine

Iodine I 131 metaiodobenzylguanidine
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INN
Drug class
Routes of administration	Intravenous
Pregnancy category
Bioavailability
Metabolism
Elimination half-life
Excretion
Legal status
CAS Number	76584-70-8
PubChem	119543
DrugBank	DB09343
ChemSpider	106731
KEGG	D01364

Iodine-131 Metaiodobenzylguanidine (I-131 MIBG) is a radiopharmaceutical used in the diagnosis and treatment of certain types of neuroendocrine tumors. It is a radioiodinated analog of the neurotransmitter norepinephrine, which allows it to be taken up by adrenergic tissue.

Chemical Structure and Properties

Iodine-131 Metaiodobenzylguanidine is a benzylguanidine derivative where the iodine-131 isotope is attached to the benzyl ring. The chemical structure allows it to mimic norepinephrine, facilitating its uptake by adrenergic neurons and neuroendocrine cells.

Mechanism of Action

I-131 MIBG is selectively taken up by adrenergic tissue due to its structural similarity to norepinephrine. Once inside the cells, the radioactive iodine-131 emits beta particles, which cause cellular damage and death. This property is utilized in the treatment of tumors that express norepinephrine transporters, such as pheochromocytoma and neuroblastoma.

Clinical Uses

Diagnostic Use

I-131 MIBG is used in scintigraphy to image neuroendocrine tumors. The uptake of the radiopharmaceutical by tumor cells allows for the visualization of tumor location and extent using a gamma camera.

Therapeutic Use

In higher doses, I-131 MIBG is used therapeutically to deliver targeted radiation to neuroendocrine tumors. This is particularly useful in cases of metastatic or inoperable pheochromocytoma and neuroblastoma, where conventional therapies may be ineffective.

Administration

I-131 MIBG is administered intravenously. The dosage and administration schedule depend on whether it is being used for diagnostic or therapeutic purposes.

Pharmacokinetics

After intravenous administration, I-131 MIBG is distributed throughout the body, with preferential uptake in adrenergic tissues. The elimination half-life of iodine-131 is approximately 8 days, and it is primarily excreted via the kidneys.

Side Effects

Common side effects of I-131 MIBG therapy include nausea, vomiting, and fatigue. Due to its radioactive nature, there is also a risk of radiation-induced damage to non-target tissues, particularly the bone marrow, which can lead to myelosuppression.

Precautions

Patients receiving I-131 MIBG therapy should be monitored for signs of bone marrow suppression and thyroid dysfunction. Thyroid protection with potassium iodide may be recommended to prevent uptake of free iodine-131 by the thyroid gland.

Contraindications

I-131 MIBG is contraindicated in patients with hypersensitivity to iodine or benzylguanidine derivatives. Caution is advised in patients with renal impairment due to the risk of increased radiation exposure.

Future Directions

Research is ongoing to improve the efficacy and safety of I-131 MIBG therapy. This includes the development of new formulations and combination therapies to enhance tumor targeting and reduce side effects.

See Also

• Radiopharmaceuticals
• Neuroendocrine tumors
• Pheochromocytoma
• Neuroblastoma

External Links

• [Link to relevant medical resources]