Development of a Rapid and Low Cost Method for Measuring Plasma Protein Binding

In drug discovery and development, it is very important to investigate the plasma protein binding (PPB) of a drug to better understand its in vivo fate. In this study, a rapid and low-cost solid-phase extraction (SPE) method was developed for determining the PPB. With this method, the total protein recovery of a blank human plasma sample was 83.7 %. The unbound drug was easily adsorbed by an ODS C₁₈ SPE column, and the recovery of three known drugs was more than 90 %. Their PPBs obtained by the SPE were identical to the value reported by conventional techniques. In addition, more than 90 % of 4-amino-2-trifluoromethyl-phenyl retinate (ATPR), which is a novel all-trans retinoic acid derivative (ATRA), was bound to human plasma protein as determined by SPE, and this value was comparable with that obtained by our previously described gel filtration-based method. Considering its versatility, speed of separation, and low cost, SPE is a rapid and economical method for measuring PPB.