Iodine-131 iobenguane

Last revised by Eric Lachance on 27 Jan 2024

Iodine-131 iobenguane, trade name Azedra, sometimes referred to as I-131 MIBG, is a theranostic (i.e. both therapeutic and diagnostic) agent used for the treatment of unresectable pheochromocytomas, paragangliomas, carcinoid, and neuroblastomas.   It is created using the high specificity Ultratrace synthesis method to produce a high proportion of MIBG bound to the radiopharmaceutical Iodine-131, allowing specific targeting of the norepinephrine transporter.


  • similar characteristics as I-131 used for thyroid treatment

  • beta minus emission – cytotoxic effects

  • gamma emission with photopeak 364 keV usable for imaging

  • half life of 8 days

Predominantly renal/urinary excretion.

I-131 iobenguane has been shown to reduce norepinephrine-secreting tumor size and alleviate metabolic effects such as hypertension from catecholamine-secreting tumors.

Pretreatment scan is performed with iobenguane scan (I-123 MIBG) to ensure a viable target. Then, a small dosimetry dose of I-131 iobenguane is used to calculate the therapeutic dose. Treatment is given via intravenous infusion in two doses, three months apart.

  • myelosuppression, including neutropenia (occasionally febrile), anemia, and thrombocytopenia

  • nausea, vomiting, fatigue

  • rare: hypothyroidism, transient hypertension (from release of hormones as tumor tissue is destroyed), decreased renal function, pneumonitis

  • not approved for pregnant patients

Azedra was FDA-approved in 2018 for the treatment of patients 12 years and older with unresectable metastatic pheochromocytomas and paragangliomas. It is manufactured by Progenics Pharmaceuticals, Inc., a Lantheus company, in the Unites States. In August 2023, Lantheus disclosed in regulatory filings that they will ultimately stop production of Azedra, continuing into the first quarter of 2024 to provide doses to current patients 6,7.

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