Iobenguane I-131 (Azedra) — Clinical FAQs

Question 1

What is Iobenguane I-131 FDA-approved to treat?

Accepted Answer

Iobenguane I-131 is FDA-approved for the following oncology indications: 1. Iobenguane-avid (MIBG-positive), unresectable, locally advanced or metastatic pheochromocytoma or paraganglioma in adults and pediatric patients ≥12 years who require systemic anticancer therapy (FDA approved July 2018; NCCN/SOFIE Phase 2 trial).

Question 2

How does Iobenguane I-131 work (mechanism of action)?

Accepted Answer

Meta-iodobenzylguanidine (MIBG) is a norepinephrine analogue that is actively taken up via the norepinephrine transporter (NET/SLC6A2) into cells derived from the neural crest, including pheochromocytoma and paraganglioma cells. When labeled with the beta-particle-emitting radionuclide iodine-131 (¹³¹I; physical half-life ~8 days), this targeted uptake delivers high-dose ionizing radiation directly to tumor cells and their microenvironment (crossfire effect), causing DNA double-strand breaks and cell death. The same mechanism underlies diagnostic MIBG scintigraphy (¹²³I-MIBG), confirming tumor avidity before therapy.

Question 3

How is Iobenguane I-131 administered?

Accepted Answer

Iobenguane I-131 is administered Intravenous (IV). Treatment consists of a mandatory dosimetric phase followed by up to two therapeutic doses.

Question 4

What are the most common side effects of Iobenguane I-131?

Accepted Answer

The most commonly reported side effects of Iobenguane I-131 (≥10% incidence) include: Fatigue (84%), Nausea (74%) — most commonly related to the administration infusion, Thrombocytopenia (51%), Neutropenia (37%), Anemia (38%) and others (10 total). Consult your oncologist for complete prescribing information.

Question 5

Does Iobenguane I-131 have a black box warning?

Accepted Answer

Yes. Iobenguane I-131 carries FDA black box warning(s) regarding: 1. Myelosuppression: severe, life-threatening, and potentially fatal thrombocytopenia and neutropenia. Monitor CBC before each dose and regularly for at least 12 weeks after each dose. Hold or reduce dose for significant cytopenias. 2. Embryo-fetal toxicity: may cause fetal harm due to ionizing radiation. Advise females of reproductive potential to avoid pregnancy. 3. Radiation risks to other individuals: patients emit ionizing radiation after dosing. Follow post-therapy radiation safety instructions to limit exposure to family members, caregivers, and the public.

Question 6

Is Iobenguane I-131 safe during pregnancy?

Accepted Answer

Iobenguane I-131 pregnancy safety: Contraindicated in pregnancy — ionizing radiation from ¹³¹I directly irradiates the fetus. Advise females of reproductive potential to use effective contraception during treatment and for 7 months after the last dose. Males should use contraception for 4 months after the last dose. Breastfeeding must be discontinued before treatment; do not resume.. Oncologists should review the complete prescribing information and discuss reproductive risks with patients before initiating therapy.

Iobenguane I-131 — Drug Monograph

Mechanism of Action

FDA Indications

Common Side Effects

Clinical Pearl

Related Therapies & Mechanisms