HIGH-PERFORMANCE FRONTAL ANALYSIS FOR THE STUDY OF PROTEIN-BINDING OFTROGLITAZONE (CS-045) IN ALBUMIN SOLUTION AND IN HUMAN PLASMA

An on-line frontal analysis HPLC system was developed for the determin ation of the unbound concentration of troglitazone (CS-045), a new ora l antidiabetic agent, in human serum albumin (HSA) solution and in hum an plasma. This system consists of a high-performance frontal analysis (HPFA) column, an extraction column, and an analytical column, which are connected via two switching valves. After the direct injection of the sample solution into the HPFA column, the drug was eluted as a zon al peak with a plateau region. The unbound drug concentration was dete rmined as the drug concentration in the plateau. As low as 0.3 nM unbo und CS-045 was determined with good reproducibility. It was found that CS-045 strongly binds with HSA, and the bound fraction in the 550 mu M HSA solution was 99.93%, which was very close to that in human plasm a (99.89%). The bound fractions were constant within the total drug co ncentration range of 1-10 mu M in the HSA solution and 250 nM-10 mu M in human plasma.