Chiral inversion of R(-) to S(+) ketoprofen in pigs

The S(+) enantiomer of ketoprofen is predominant in the plasma of pigs after administration of racemic ketoprofen, although the occurrence and extent of R(-)-to-S(+) inversion is uncertain. Plasma concentrations of both enantiomers were measured and percentages of S(+) ketoprofen were calculated at different time points after intravenous and oral dosing of pigs with 1.5mg/kg R(-) ketoprofen. S(+) ketoprofen was formed immediately after administration and concentrations exceeded R(-) concentrations after 1h. Absence of pre-systemic inversion was deduced from the lower S(+) percentages after oral administration. A rapid and increasing inversion, reaching a maximum of about 70%, occurred and appeared to be responsible for the predominance of S(+) ketoprofen in pig plasma after administration of the racemate.