ABSTRACT
A common reaction seen in drug metabolism is hydroxylation of aromatic rings. The use of radiotracers for in vivo experiments is more prevalent than for in vitro experiments. When administering radiotracers to humans, however, there are strict regulatory limits on the amounts of radioactivity that can be given. The chapter explains how radiotracers are applied to the conduct of drug metabolism studies. It presents certain knowledge of pharmacokinetics and the types of biotransformations commonly seen in drug metabolism. Tritium is a commonly used radiotracer in drug metabolism. For in vivo drug metabolism studies, the first choice of radiolabel is 14C. There are risks in predicting drug metabolism from in vitro models, as they are not always predictive of the metabolism in vivo. For in vivo studies using oral administration, ideally the dose is administered as a solution. Intravenous doses are prepared in physiological saline, glucose, or certain specialized formulations specifically designed for intravenous administration.
