ABSTRACT
This chapter focuses on the techniques used to characterize the in vitro metabolism of drugs. Although many enzymes may play some role in drug metabolism, it also focuses on the cytochrome P450 (P450) enzymes. The chapter discusses both Michaelis-Menten kinetics and more complex kinetics, presents general experimental protocols that can be used to obtain and analyze kinetic data and examines the implications of the results when predicting drug interactions. Most new drugs enter clinical trials with varying amounts of information on the human enzymes that may be involved in their metabolism. Most of this information is obtained from animal studies, human tissue preparations in conjunction with chemical inhibitors or antibodies, and expressed enzymes. If non-Michaelis-Menten kinetics for all P450 enzymes are a result of multiple substrates binding to the enzyme, then the reaction kinetics for the binding of two substrates to an active site can be complicated. Most P450-catalyzed reactions show hyperbolic saturation kinetics and competitive inhibition kinetics.
