Technetium (99mTc) sestamibi

Technetium (^99mTc) sestamibi

Systematic (IUPAC) name
Hexakis(2-methoxy-2-methylpropylisonitrile) technetium (99mTc)
Identifiers
CAS number	109581-73-9
ATC code	V09GA01
PubChem	5384
Chemical data
Formula	C36H66N6O6Tc
Mol. mass	777.852 g/mol
Pharmacokinetic data
Bioavailability	NA
Protein binding	1%
Metabolism	Nil
Half life	Variable
Excretion	Fecal (33%) and renal (27%)
Therapeutic considerations
Licence data	US FDA:link
Pregnancy cat.	C(US)
Legal status	℞-only(US)
Routes	Intravenous

Technetium (^99mTc) sestamibi (trade name Cardiolite) is a pharmaceutical agent used in nuclear medicine imaging. The drug is a coordination complex of the radioisotope technetium-99m with the ligand methoxyisobutylisonitrile (MIBI). The generic drug became available late September 2008. A scan of a patient using MIBI is commonly known as a MIBI scan.

Its main use is for imaging the myocardium (heart muscle). It is also used in the work-up of primary hyperparathyroidism to identify parathyroid adenomas, for radioguided surgery of the parathyroid and in the work-up of possible breast cancer.

Cardiac imaging

Technetium (^99mTc) sestamibi is a lipophilic cation which, when injected intravenously into a patient, distributes in the myocardium proportionally to the myocardial blood flow. Single photon emission computed tomography (SPECT) imaging of the heart is performed using a gamma camera to detect the gamma rays emitted by the technetium-99m as it decays. Two sets of images are acquired. For one set, ^99mTc MIBI is injected while the patient is at rest and then the myocardium is imaged. In the second set, the patient is stressed either by exercising on a treadmill or pharmacologically. The drug is injected at peak stress and then imaging is performed. The resulting two sets of images are compared with each other to distinguish ischemic from infarcted areas of the myocardium. This imaging technique is also known as myocardial perfusion imaging (MPI).

Sestamibi was previously thought to not redistribute because earlier studies looked at individuals with no ischemia. The washout or redistribution rate for such individuals was approximately 20%, with half of this (10%) the result of technetium-99m decay over 55 minutes. It is now known that sestamibi redistributes more under conditions of ischemia. Specifically, the count activity increases at 60 minutes compared with 5 minute images when critical narrowing of coronary arteries is present. This explains why 40,000-70,000 Americans were told, based upon the 60 minute image, that they did not have heart disease, when in fact they had severe disease.^[1]

With dipyridamole (Persantine MIBI scan)

When combined with the drug dipyridamole, a brand name of which is Persantine, a MIBI scan is often referred to as a Persantine MIBI scan.

Parathyroid imaging

In primary hyperparathyroidism, one or more of the four parathyroid glands either develops a benign tumor called an adenoma or undergoes hypertrophy as a result of homeostatic dysregulation. The parathyroid gland takes up ^99mTc MIBI following an intravenous injection, and the patient's neck is imaged with a gamma camera to show the location of all glands. A second image is obtained after a washout time (approximately 2 hours), and mitochondria in the oxyphil cells of the abnormal glands retaining the ^99mTc are seen with the gamma camera. This imaging method will detect 75 to 90 percent of abnormal parathyroid glands in primary hyperparathyroidism. An otolaryngologist or an endocrine surgeon can then perform a directed parathyroidectomy (less invasive than traditional surgery) to remove the abnormal gland.

Breast imaging

The drug is also used in the evaluation of breast nodules. Malignant breast tissues concentrate ^99mTc MIBI to a much greater extent and more frequently than benign disease. As such, limited characterization of breast anomalies is possible. Scintimammography has a high specificity for breast cancer, and has a sensitivity of 66% based on positive biopsy compared to mammography and ultrasound with a 29% positive biopsy.^{[citation needed]}

Radioguided surgery of the parathyroids

Following the administration of ^99mTc MIBI it collects in overactive parathyroid glands. During surgery, the surgeon can use a probe sensitive to gamma rays to locate the overactive parathyroid before removing it.^[2]

See also

• Sestamibi scan

References

This article's citation style may be unclear. The references used may be made clearer with a different or consistent style of citation, footnoting, or external linking. (November 2009)

1. ^ Fleming, et al.
2. ^ Untch, B. R.; Barfield, M. E.; Bason, J.; Olson Jr, J. A. (2007). "Minimally Invasive Radio-guided Surgery for Primary Hyperparathyroidism". Annals of Surgical Oncology 14 (12): 3401–3402. doi:10.1245/s10434-007-9519-0. PMID 17899291.  edit

• Cardiolite.com
• Dilon Breast-Specific Gama Imaging
• Miraluma
• Myoview.com
• Parathyroid.com
• Pharmalucence Inc.

• POLATOM.PL