(I-oh-BEN-gwayn …) 
A drug that contains a form of radioactive iodine and is used to treat adults and children aged 12 years and older with certain types of malignant pheochromocytoma or paraganglioma that have spread or cannot be removed by surgery. It is also being studied in the treatment of other types of cancer. Iobenguane I 131 builds up in tumor cells and gives off radiation that may kill them. It is a type of radiotherapeutic agent. Also called 131I-MIBG, Azedra, and iodine I 131-metaiodobenzylguanidine.