Application of radioisotopes in drug absorption, distribution, metabolism and excretion (ADME) studies and general metabolism related investigations - Part II. Practical aspects

In part I of this article, the principles and detection methods for radioisotopes were reviewed. In part II of this article, the practical aspects of radioisotope applications will be discussed including some real situations that our organization has faced previously to highlight the role of experience in conjunction with the right tools to address these scientific challenges. Specifically, the following key points are discussed in Part II: absorption, distribution, metabolism and excrretion (ADME) of radiolabeled drugs in animals and human; the tissue distribution using traditional and quantitative whole body autoradiography (QWBA) techniques; qualitative and quantitative metabolite profiling in in vitro and in vivo drug metabolism studies; the semi-quantitative determination of human metabolites in non-radiolabeled study samples via radiolabeled metabolite standards; the application of radiolabeled compounds in reaction phenotyping and enzyme kinetic studies; the application of radiolabeled compounds in plasma protein binding and blood-plasma distribution ratio studies; the use of radiolabeled cofactor or trapping agents for detection of reactive metabolite(s); and the determination of structures and formation pathways of secondary metabolites from radiolabel drug studies.