Drug Partition in Red Blood Cells

This chapter will focus on the techniques used in the evaluation of red blood cell partitioning/binding (RCB) of drugs in discovery and development. Certain therapeutic compounds have a high degree of affinity for the red blood cell fraction of whole blood and have large RBC-to-plasma concentration ratios. Knowledge of in vitro RBC partitioning of compounds is important to the interpretation and understanding of the compounds pharmacokinetic profile and distribution in vivo. The goals of this chapter will be to examine some of the current methods used in the evaluation of red cell partitioning and the determination of blood-to-plasma ratios at the discovery level of development where species comparisons can be an important determinant in the design and interpretation of some observed pharmacokinetic study results. Methods employing the use of both radiolabeled and cold materials will also be discussed using a variety of analytical tools.