Pharmacokinetics of ibuprofen enantiomers after single and repeated doses in man

The pharmacokinetic parameters of ibuprofen enantiomers after a single 600 mg dose and repeated 3 x 400 mg doses of Nurofen were determined in 12 healthy volunteers. Terminal half-lives were similar for both enantiomers, but plasma levels of S-ibuprofen were higher than those of R-ibuprofen, due to the chiral inversion and differences in distribution and metabolism. Comparison of maximal concentrations and areas under the concentration vs time curves between the first and last doses for each enantiomer indicated linear pharmacokinetics with no time-dependency. A large inter-individual variability in the ratio of S- to R-ibuprofen average concentrations at steady-state was observed (mean +/- SD 1.89 +/- 0.89) and probably accounts for the known lack of correlation between racemic ibuprofen concentrations and therapeutic efficacy.