Chapter 21 Breath test: Drug metabolism studies

Abstract

This chapter highlights drug metabolism studies with breath test. The major advantages of stable isotopically labeled (SIL) molecules are the absence of radioactivity and hazard generated by radiations. The breath test concept relies on the administration of a specific 13 C-labeled substrate whose metabolic utilization is monitored by measuring the elimination of 13 CO 2 in the expired breath gases. This substrate acts as a metabolic probe whose target is the biological system which is implicated in the consumption of this substrate and, more specifically, of its labeled functional groups. Information's on the integrity or changes of this particular biological system can be obtained from correlations existing between the kinetics of 13 CO 2 elimination and the functional capacity of the system. Very low levels of stable isotopes and isotope ratios can be measured accurately and with a high precision from micro-samples using continuous flow isotope ratio mass spectrometry coupled with gas chromatography. Isotope ratio mass spectrometers are designed for the continuous analysis of adjacent ion beams which necessitates a very high stability. These ions correspond to gas formed from the molecule to be analyzed.