Assessment of Drug Plasma Protein Binding in Drug Discovery

Determination of plasma protein binding is important in drug discovery and development for developing PK-PD relationships, and projecting clinical doses because the free drug concentration at the site of action is responsible for the pharmacological activity. This chapter will describe various methods commonly used for the in vitro determination of plasma protein binding including classical equilibrium dialysis (CED), rapid equilibrium dialysis (RED), and ultrafiltration Nonspecific binding and mass balance methods used to recover or prevent the loss of compound due to binding to the wall and/or membrane of the apparatus will be briefly discussed as well. Finally, the techniques will be discussed in relation to the type of study required and the method of analysis of both the bound (plasma) and free-fraction (buffer) components and the analytical procedures needed for the quantification of concentrations in these matrices. Techniques using both radiolabeled and cold compounds will be presented as both are usually available at the early or late discovery phases and employ different methods of analysis.