I-123 MIBG is provided as a freeze-dried, radio-labeled sterile powder. The powder is reconstituted with 2 mL of sterile normal saline. The dose should be measured using a dose calibrator prior to administration. Caution: Radioactive Material. A commonly used name for iobenguane is meta-iodobenzylguanidine or MIBG.

Iobenguane or meta-iodobenzylguanidine (MIBG) is a physiological analog of the guanidines, such as guanethidine and phenethylguanidine. In adrenergic nerves, guanidines are believed to share the same transport pathway as norepinephrine and to accumulate in, and displace norepinephrine from, intraneuronal storage granules. Similarly, I-123 MIBG is concentrated in, stored in, and released from chromaffin granules. The retention of I-123 MIBG in the adrenal medulla may be a result of their uptake in adrenergic neurons and subsequent sequestration into chromaffin storage granules. Due to their selective uptake mechanism, I-123 MIBG allows specific detection and localization of neuroendocrine tumors and adrenal medullary hyperplasia. The gamma emissions given off by I-123 MIBG allow detection of adrenergic tumors by scintigraphy. Medullary thyroid carcinoma: Although the mechanism of I-123 MIBG uptake by medullary thyroid carcinoma (MTC) is not completely understood, it has been found that MTC can produce catecholamines (epinephrine and norepinephrine). Therefore, I-123 MIBG could be taken up and stored in catecholamine vesicles of MTC.

Iobenguane is indicated as a radioactive isotope diagnosing for adrenomedullary disorders and neuroendocrine tumors.

Tumors, adrenal medulla (diagnosis): I-123 MIBG is used for diagnostic imaging of the adrenal medulla, for the evaluation and localization of intra- and extra-adrenal pheochromocytomas, paragangliomas, and neuroblastomas, as well as for localization of metastatic lesions from these tumors. I-123 MIBG can also be used for confirmation of diagnosis of pheochromocytoma when catecholamine determination tests are unclear.

Tumors, carcinoid (diagnosis): I-123 MIBG scintigraphy is used as screening procedures for suspected carcinoid tumors, especially those of intestinal origin.

Hyperplasia, adrenal medulla (diagnosis): I-123 MIBG is used in the evaluation of the adrenal medulla for disorders such as medullary hyperplasia in patients at risk of developing medullary disease (e.g., multiple endocrine neoplasia [MEN type 2, MEN type 3]).

Carcinoma, thyroid (diagnosis): I-123 MIBG is used for diagnostic imaging of medullary thyroid carcinoma.

DISTRIBUTION

After intravenous administration, there is rapid uptake of MIBG mainly in the liver, and in lesser amounts in the lungs, heart, and salivary glands. A limited number of patients may show activity in normal adrenals, lung, skeletal, muscle, and blocked thyroid glands. Although the uptake in normal adrenal glands is very low, hyperplastic adrenals and tumors such as pheochromocytoma, neuroblastoma, and other tumors with neurosecretory granules have a relatively higher uptake. Significant clearance of I-123 MIBG from the liver and the spleen occurs within 72 hours. I-123 MIBG—In adrenal medullary tumors: Initial images may be obtained 2 to 3 hours after injection. Images may also be obtained at 18 to 24 hours, and as late as 48 hours post injection. Most pheochromocytomas are visualized at 24 hours. However, due to the short half-life of I-123 MIBG, images may not be possible at times when background (e.g., liver) activity is low and imaging would be optimal. Small amounts of radioactivity used in diagnosis; radiation received is low and considered safe.

ELIMINATION

Renal; about 40 to 50% of the injected activity is eliminated within 24 hours and about 70 to 90% within 4 days (mainly as unchanged drug with small amounts of I-123 m-iodohippuric acid [I-123 MIHA], I-123 iodide, and I-123 m-iodobenzoic acid [I-123 MIBA]).

At present, there are no known side/adverse effects associated with the use of diagnostic dosages of I-123 MIBG.

PREPARATION FOR THIS TEST

Special preparatory instructions may apply; patient should inquire in advance.

Administration of potassium iodide or Lugol’s solution one day before administration of I-123MIBG and for 6 days after administration to prevent or reduce thyroid uptake of radioiodide contaminant.

GENERAL DOSAGE INFORMATION

Radiopharmaceuticals are to be administered only by or under the supervision of physicians who have had extensive training in the safe use and handling of radioactive materials and who are authorized by the Nuclear Regulatory Commission (NRC) or the appropriate State agency, if required, or, outside the U.S., the appropriate authority. To minimize uptake of radioactive iodine by the thyroid, potassium iodide (SSKI, 60 mg twice a day) or Lugol's solution (1 drop three times a day) may be used, beginning at least 24 hours before and continuing for 6 days after administration of I-123 MIBG.

Safety considerations for handling this radiopharmaceutical:

Improper handling of this radiopharmaceutical may cause radioactive contamination. Guidelines for handling radioactive material have been prepared by scientific, professional, state, federal, and international bodies and are available to the specially qualified and authorized users who have access to radiopharmaceuticals.

IOBENGUANE I-123 INJECTION

Usual adult administered activity for diagnosis of tumors or medullary disease:

Intravenous, 370 megabecquerels (10 millicuries) of I-123 mIBG, with a minimum specific activity of 740 megabecquerels to 1.3 gigabecquerels (20 to 35.6 millicuries) per mg (at time of calibration), administered over a period of fifteen to thirty seconds.

Usual pediatric administered activity for diagnosis of tumors or medullary disease:

In children up to 18 years of age, dosage must be individualized by physician.

Usual geriatric administered activity:

See usual adult administered activity.

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