High-performance frontal analysis for the study of protein binding of troglitazone (CS-045) in albumin solution and in human plasma

Abstract

An on-line frontal analysis HPLC system was developed for the determination of teh unbound concentration of troglitazone (CS-045), a new oral antidiabetic agent, in human serum albumin (HSA) solution and in human 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 zonal peak with a plateau region. The unbound drug concentration was determined as the drug concentration in the plateau. As low as 0.3 n M unbound CS-045 was determined with good reproducibility. It was found that CS-045 strongly binds with HSA, and the bound fraction in the 550 μ M HSA solution was 99.93%, which was very close to that in human plasma (99.89%). The bound fractions were constant within the total drug concentration range of 1–10 μ M in the HSA solution and 250 n M–10 μ M in human plasma.