133Xe-Xenon (Gas)

Description
¹³³Xe-Xenon serves as a diagnostic radiopharmaceutical. It is primarily used as a gas (5% diluted in carbon dioxide) for evaluating pulmonary function and lung imaging. Additionally, a saline solution form allows its use in cerebral blood flow assessment.

Clinical Applications
The gas form of ¹³³Xe-Xenon helps in lung ventilation imaging. Typical doses for this purpose range from 2 to 25 mCi, administered through inhalation. In its saline form, the drug assesses cerebral blood flow, using doses of 10 to 30 mCi administered intravenously.

Availability and Pricing
Availability of ¹³³Xe-Xenon has changed over time. Major European suppliers like BMS and Mallinckrodt withdrew their products by 2003. Currently, CISbio retains market authorization but withdrew from many markets. In the United States, Lantheus reintroduced the product in 2018 after holding a monopoly. Japan’s Fuji Film and Nihon Medi Physics also offer versions of this radiotracer.

¹³³Xe is sold in single-dose formats (10–25 mCi) or multidose formats (up to 200 mCi). As of 2020, a single dose costs approximately $240 in the United States. The drug is produced as a byproduct of ⁹⁹Mo manufacturing, but shortages of 99Mo have not significantly affected its supply due to low demand.

Competition and Alternatives
The use of ¹³³Xe-Xenon has declined. Physicians now prefer alternatives like ^99mTc-Pentetate (^99mTc-DTPA) for ventilation imaging. ^99mTc-Technegas is expected to enter the US market after completing trials, with availability already established in Europe and Australia.

Comments
Manufacturing issues with albumin macroaggregates made ¹³³Xe a temporary substitute for pulmonary imaging in the US. However, its use remains niche. Its chemical inertness limits applications since it cannot combine with organic molecules. Historically, ¹³³Xe competed with ¹²⁷Xe, which provided higher resolution and lower dosimetry. However, ¹²⁷Xe was removed from markets, and ¹³³Xe availability remains limited to specialized cases.