Enzyme Kinetics of Drug‐Metabolizing Reactions and Drug–Drug Interactions

Abstract

In vitro studies play an important role in characterizing biotransformation reactions. Kinetic parameters are determined during the early phases of drug discovery and development and provide invaluable information needed to predict in vivo metabolism and assess potential interactions with enzyme effectors. In order to obtain reliable and accurate in vitro data that reflect the in vivo situation, one must employ well‐defined enzyme kinetic practices and reaction conditions. There are multiple factors to consider when conducting in vitro kinetic experiments such as enzyme concentration, addition of co‐substrates, buffering systems, and the effects that each of these may have on the experimental results. Of equal importance is to be aware of the potential caveats that may lead to erroneous results. An overview of the appropriate experimental conditions for kinetic studies is described, as well an explanation of which kinetic model is most appropriate when describing the kinetic results. Kinetic characterizations of most enzymatic reactions are governed by hyperbolic kinetics that can be described by the Michaelis–Menten equation. In some instances, atypical kinetic profiles have been observed. Atypical kinetics may result from multiple substrate molecules occupying the enzyme active site simultaneously. An overview of the fundamental concepts underlying both typical and atypical kinetic analysis is provided. In addition, the graphical representation and interpretation of the data is reviewed. In summary, the focus of this chapter is on general enzyme kinetic principles. These principles are presented in the context of defining drug metabolic clearance and drug inhibition potential. It is our hope to provide valuable insight into the complexities of in vitro kinetics and the many challenges that surround quantitative prediction in drug metabolism.

Unraveling Interspecies Differences in the Phase I Hepatic Metabolism of Alternariol and Alternariol Monomethyl Ether: Closing Data Gaps for a Comprehensive Risk Assessment

“…The ratio between the resulting V max and K m values�often referred to as the in vitro intrinsic clearance�provides a relative analysis of the metabolization efficiencies. 37 With both curvefitting methods, AOH seems to be metabolized the slowest in pigs, followed by humans and rats. The phase I biotransformation efficacy order for AME is similar to that of AOH according to the Michaelis−Menten model.…”