Two studies were carried out to evaluate drug distribution in the gut and in the lung. Producing a true tracer situation is important to these studies. In the analysis of modified-release formulations, drugs such as dilti-azem are formulated with small amounts of stable [152Sm]-samarium oxide. The tablets can then be activated by neutron activation to produce radioactive 153Sm and followed in vivo using planar imaging. This Phase I study allowed quantitative distribution of the tablet in the gastrointestinal tract . In another example, the lung distribution of the corticosteroid tri-amcinolone acetonide was studied using the dispenser Azmacort, a pressurized aerosol metered-dose inhaler formulation. The steroid was radiolabelled with 11C and introduced into the dispenser. The time-activity curve obtained using PET showed a significant increase of the steroid in the lung and a significant decrease in the mouth (Fig. 17.3). These data were submitted to the FDA in support of the Azmacort inhaler's superiority .
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