Binding of ketoprofen enantiomers in various human albumin preparations

Published data conflict with respect to the enantioselective protein bindin g parameters of R(-) and S(+) ketoprofen. We studied whether differences in experimental conditions used and/or presence of interfering compounds coul d provide a possible explanation for these discrepancies. Equilibrium dialy sis, supported by ultrafiltration (67 mM Sorensen phosphate buffer pH 7.4, 580 mu M HSA, 37 degrees C) allowed the characteristics of the binding site s to be determined according to Scatchard's analysis. (R) and (S)-ketoprofe n concentrations were measured by HPLC. The free (R)-ketoprofen/free (S)-ke toprofen (F-R/F-S) concentration ratio was calculated. The effect of octano ic acid (OA) found in currently marketed intravenous HSA solutions, and hip puric acid (HA), on F-R/F-S concentration ratio was considered. Two classes of binding sites were characterized for both enantiomers. The free (S)-ket oprofen concentrations remained equal to those of the (R)-antipode at low c oncentrations of racemate (2-35 mu g ml(-1)) indicating non-stereoselective albumin binding over the therapeutic range. From 35 mu g ml(-1): the free (S)-ketoprofen concentrations were slighty greater than those of its antipo de. Both OA and HA induced an increase of the free fraction of the enantiom ers by a two-fold to a 15-fold order of magnitude. OA, but not HA, showed a more pronounced effect for the (S)-form leading to a marked decrease in F- R/F-S concentration ratio (0.61). Differences in HSA preparations used and/ or the presence of interfering compounds may explain the variability in the reported protein binding characteristics of ketoprofen enantiomers. (C) 20 00 Elsevier Science B.V. All rights reserved.