Preface

Drug metabolism comprises the identification, characterization, and quantification of the chemicals or compounds produced in an animal or human upon administration of a drug. Research practices not only require the chemical structure but also aim to determine the pharmacological activities and/or toxicity of these compounds. This is first performed in animals, as studies attempt to identify and quantify metabolites, and later in humans, with care to further characterize metabolites that are either unique to or produced disproportionately in humans compared to animals. Characterization includes the determination of enzyme systems or other biological mechanisms that produce each identified metabolite; this information is used to predict potential drug-drug interactions with other compounds that increase or decrease metabolite formation and sources of biological variability in response or toxicity with varying patient genetics, which affect CYP isoform expression. This book's purpose is to provide a better understanding of the biology and current technology applied in the field of drug metabolism.

*Drug Metabolism* begins with a review of the various structures and functions of the human liver in the chapter entitled *Hepatocytes and Their Role in Metabolism*. The information covered in this chapter is key to understanding the basic principles involved in the metabolism of drugs at the organ, the cellular, the organelle, and the enzymatic levels. In the chapter *Drug Metabolism in Drug Discovery and Preclinical Development*, the metabolism-related approaches and technology involved before and after the identification of a lead compound are described. This chapter is an up-to-date accounting of how studies relating to drug metabolism are conducted in early drug development.

The second part of the book includes more specialized foci within the realm of drug metabolism. The chapter *From Pharmacogenetics to Gene Expression: Implications for Precision Medicine in Diabetes* examines how drugs and their metabolism are affected by alternate phenotypes among individuals. Furthermore, the chapter *Metabolism of Phytochemicals* is also a description of the highly specialized area of drug metabolism dealing with potential medicinal compounds found in plants. Finally, the chapter In vitro *Metabolic Stability of Drugs and Applications of LC-MS in Metabolite Profiling* is an in-depth look at how liquid chromatography with mass spectrometry detection is applied in quantifying and characterizing potential metabolite species after administration of a drug.

> **Katherine Dunnington Ph.D.** Celerion, Data Management and Biometrics Lincoln, Nebraska, United States

Section 1
