Protein binding of some nonsteroidal anti-inflammatory drugs studied by high-performance liquid affinity chromatography.

The protein binding of indomethacin, sulindak and diclofenac sodium is studied in the presence of some competitors: phenylbutazon and diazepam. A high-performance liquid affinity chromatography based on chiral stationary phases with immobilized human serum albumin is used. The competition of the markers and the drugs for two major high- and low-affinity binding sites is investigated. Using a mathematical procedure proposed by the same authors in a previous work the affinity constants of the binding drugs and markers for both types of site are calculated. An analogous behaviour is established for the three drugs-they have nearly the same affinity for the primary binding sites marked by phenylbutazon and diazepam and only one type of low-affinity site (diazepam-binding sites) is involved in binding. That can be explained assuming an overlapping sites.