The P450 enzyme system: a key to understanding the metabolism of drugs

A variety of mechanisms is available to counter any invasion of the body by drugs or other foreign substances. These include delivery to body tissues such as adipose tissue which defers the degradation process; biotransformation mediated by enzymes located primarily, but not exclusively, in liver microsomes; and excretion via the kidneys, lungs, biliary tract, secretory glands and organs. It is important to realize that biotransformation is not necessarily detoxification or degradation. Several other pathways are possible, such as transforming an inert parent compound into a pharmacologically active metabolite; and converting an active compound into another substance of similar or greater activity.