HPLC on Chiralcel OJ-R for Enantiomer Separation and Analysis of Ketoprofen, from Horse Plasma, as the 9-Aminophenanthrene Derivative

Racemic ketoprofen is a non‐steroidal anti‐inflammatory drug used to treat musculoskeletal and colic conditions in horses. The enantioselective chiral inversion of ketoprofen administered to horses has been studied by use of cellulose tris(4‐methylbenzoate), also known as Chiralcel OJ‐R, as chiral stationary phase; acetonitrile − 0·02 m perchlorate buffer (pH 2·0) ‐ methanol, 60:15:25 (v/v/v) was used as mobile phase. Before chromatography, to effect adequate chiral interaction with the chiral stationary phase ketoprofen was derivatized with 9‐aminophenanthrene, under acid conditions, after solid‐phase (C18) extraction and then liquid–liquid extraction, to ensure effective removal of endogenous plasma materials. The 9‐aminophenanthrene derivative of S‐ibuprofen was used as internal standard. The enantiomers of ketoprofen were separated to baseline (Rs = 6·44, α = 1·76) within a short analysis time. The results indicate that the bio‐inversion of R‐ketoprofen to the S isomer is significant in equine species. However, considerable differences in pharmacokinetic parameters were observed, indicating large inter‐animal variation.