Enantiospecific pharmacokinetics and pharmacodynamics of ketoprofen in sheep

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Abstract
Pharmacokinetic and pharmacodynamic parameters were established for the enantiomers of the 2‐arylpropionic acid (APA) nonsteroidal anti‐inflammatory drug (NSAID), ketoprofen (KTP). Each enantiomer was administered separately (1.5 mg/kg) and in a racemic mixture (3 mg/kg) intravenously (i.v.) to a group of eight sheep in a four‐way, four‐period cross‐over study using a tissue cage model of inflammation. Plasma disposition of each KTP enantiomer was similar following separate administration of the pure compounds compared to administration of the racemic mixture. S(+)KTP volume of distribution (Vdarea) was higher and clearance (ClB) faster than those of R(–)KTP. S(+) and R(–) KTP achieved relatively low concentrations in exudate and transudate. Unidirectional limited chiral inversion of R(–) to S(+)KTP was demonstrated. After R(–)KTP administration S(+)KTP was detected in plasma, but not in either exudate or transudate.Pharmacokinetic/pharmacodynamic (PK/PD) modelling of the data could not be undertaken following R(–)KTP administration because of chiral inversion to S(+)KTP, but the pharmacodynamic parameters, calculated maximum effect (Emax), concentration producing 50% effect (EC50), Hill’s coefficient (N), rate constant of elimination of drug effect from the compartment (KeO) and mean equilibration half‐life (t½Ke0) were determined for S(+)KTP after administration of the racemic mixture as well as the pure compound.