ABSTRACT
This chapter outlines studies to determine a drug’s metabolism which are conducted separately from the clinical studies. It presents the timing of drug metabolism studies. The use of radiotracers is only one tool of many used by the pharmaceuticals industry in the science-driven drug registration process. Before embarking on the subject of radiotracers, however, it is worth setting the scene with a general overview of the various stages of drug registration. How radiotracers are applied to this process can be placed into context. Without radiotracers, the elucidation of many biochemical pathways would have been extremely difficult, if not impossible. Radiotracers are used to follow the metabolic fate of a drug through a test system where otherwise it would be difficult or impossible to distinguish the drug from its surroundings. For convenience, regulatory drug testing programs that utilize radiotracers can be divided into two groups: standard studies and explorative studies.
