Iobenguane

Iobenguane

Systematic (IUPAC) name
1-(3-iodobenzyl)guanidine
Clinical data
Legal status	℞ (Prescription only)
Routes of administration	Intravenous
Identifiers
CAS Number	77679-27-7 N
ATC code	V09IX01 (123I) V09IX02 (131I, diagnostic) V10XA02 (131I, therapeutic)
PubChem	CID 60860
ChemSpider	54847 N
UNII	35MRW7B4AD Y
ChEMBL	CHEMBL818 N
Synonyms	meta-iodobenzylguanidine mIBG, MIBG
Chemical data
Formula	C8H10IN3
Molar mass	275.09 g/mol
SMILES C1=CC(=CC(=C1)I)CNC(=N)N
InChI InChI=1S/C8H10IN3/c9-7-3-1-2-6(4-7)5-12-8(10)11/h1-4H,5H2,(H4,10,11,12) N Key:PDWUPXJEEYOOTR-UHFFFAOYSA-N N
NY (what is this?)  (verify)

Iobenguane, also known as metaiodobenzylguanidine or mIBG, or MIBG (tradename Adreview) is a radiopharmaceutical,^[1] used in a scintigraphy method called MIBG scan. Iobenguane is a radiolabeled molecule similar to noradrenaline.

The radioisotope of iodine used for the label can be iodine-123 (for imaging purposes only) or iodine-131 (which must be used when tissue destruction is desired, but is sometimes used for imaging also).

Pheochromocytoma seen as dark sphere in center of the body (it is in the left adrenal gland). Image is by MIBG scintigraphy, with radiation from radioiodine in the MIBG. Two images are seen of the same patient from front and back. Note dark image of the thyroid due to unwanted uptake of iodide radioiodine from breakdown of the pharmaceutical, by the thyroid gland in the neck. Uptake at the side of the head are from the salivary glands. Radioactivity is also seen in the bladder, from normal renal excretion of iodide.

It localizes to adrenergic tissue and thus can be used to identify the location of tumors^[2] such as phaeochromocytomas and neuroblastomas. With I-131 it can also be used to eradicate tumor cells that take up and metabolize norepinephrine.

Thyroid precautions

Thyroid blockade with (nonradioactive) potassium iodide is indicated for nuclear medicine scintigraphy with iobenguane/mIBG. This competitively inhibits radioiodine uptake, preventing excessive radioiodine levels in the thyroid and minimizing the risk of thyroid ablation ( in the case of I-131). The minimal risk of thryoid carcinogenesis is also reduced as a result.

The FDA-approved dosing of potassium iodide for this purpose are as follows: infants less than 1 month old, 16 mg; children 1 month to 3 years, 32 mg; children 3 years to 18 years, 65 mg; adults 130 mg.^[3] However, some sources recommend alternative dosing regimens.^[4]

Not all sources are in agreement on the necessary duration of thyroid blockade, although agreement appears to have been reached about the necessity of blockade for both scintigraphic and therapeutic applications of iobenguane. Commercially available iobenguane is labeled with iodine-123, and product labeling recommends administration of potassium iodide 1 hour prior to administration of the radiopharmaceutical for all age groups,^[5] while the European Associated of Nuclear Medicine recommends (for iobenguane labeled with either I-131 or I-123,) that potassium iodide administration begin one day prior to radiopharmaceutical administration, and continue until the day following the injection, with the exception of new-borns, who do not require potassium iodide doses following radiopharmaceutical injection.^[4]

Product labeling for diagnostic iodine-131 iobenguane recommends potassium iodide administration one day before injection and continuing 5 to 7 days following.^[6] Iodine-131 iobenguane used for therapeutic purposes requires a different pre-medication duration, beginning 24–48 hours prior to iobenguane injection and continuing 10–15 days following injection.^[7]

Alternative imaging modality for pheochromocytoma

The FDOPA PET/CT scan has proven to be nearly 100% sensitive for detection of pheochromocytomas, vs. 90% for MIBG scans.^[8][9][10] Centers which offer FDOPA PET/CT, however, are more rare.

References

External links

• Iodine 131-metaiodobenzylguanidine at the NCI Drug Dictionary