ABSTRACT
Metabolism is a fundamental process in the body that transforms drugs and other foreign substances (xenobiotics), as well as endogenous substances, into entities that can be excreted or sometimes recycled. Metabolism transforms drugs and xenobiotics into more polar, water-soluble products that can be excreted in the urine, for example, and the products are generally (but not always) less toxic and less pharmacologically active. Pharmaceutical manufacturers usually anticipate and evaluate the pharmacological actions of all major metabolites of a drug before obtaining approval by the Food and Drug Administration (FDA) for a New Drug Application. This chapter focuses on a key player of metabolic reactions, the cytochrome P450 enzyme system. The cytochromes P450 are families of heme proteins present in a large number of cell types and are also very widespread in nature. Many xenobiotics, including drugs, can inhibit metabolic enzymes.
