Human pharmacokinetics of ibuprofen enantiomers following different doses and formulations: intestinal chiral inversion

Bidirectional chiral inversion of the enantiomers of the nonsteroidal antiinflammatory drug oxindanac in dogs

The nonsteroidal antiinflammatory drug oxindanac exists as two enantiomers, with most of its pharmacological activity residing in the (S)-isomer. The behavior of its enantiomers was investigated in dogs. Bidirectional inversion occurred in heparinised plasma and blood, with a ratio of enantiomers [S:R] of 7.3:1 being achieved at equilibrium after incubation for 24 h at 37 degrees C. There was no detectable inversion of either isomer in plasma incubated at 4 degrees C for up to 8 h or in aqueous solution at 37 degrees C for up to 36 h. Bidirectional inversion also occurred in vivo, with a ratio of plasma AUC (0 infinity)s [S:R] of 8.1:1. The ratio of enantiomers reached equilibrium within 2 hr following (S)- or rac-oxindanac, and within 8 h following (R)-oxindanac. Elimination t1/2s of the isomers were the same (R, 12.1 h, S, 13.3 h). There were no differences in the ratio of enantiomers following oral or intravenous application, suggesting that a systemic site for inversion was predominant. Although concentrations of the respective isomers were similar at equilibrium following administration of either (R)-, (S)-, or rac-oxindanac, AUC (0 infinity)s differed due to the delay in reaching equilibrium. The extent of inversion to the (S)-isomer was 100, 73.2, and 60.7% after administration of (S)-, rac-, and (R)-oxindanac, respectively. Although pharmacological activity might be equivalent at equilibrium following administration of either (R)-, (S)-, or rac-oxindanac; efficacy at early time points should be superior in the order (S) > racemate > (R).(ABSTRACT TRUNCATED AT 250 WORDS)

Ketoprofen pharmacokinetics in the elderly: influence of rheumatic disease, renal function, and dose

An age-related accumulation of ketoprofen due to a reduced clearance has been reported in the elderly. Other studies have not observed these changes in the kinetics of unchanged ketoprofen, but have reported increased plasma levels and reduced urinary excretion of conjugated ketoprofen. The authors examined the effects of dose, renal function, and the presence of arthritis on the stereoselective kinetics of ketoprofen in five nonarthritic and six arthritic elderly subjects. There was a significant difference in renal function (CLCr, mL/min; arthritic, 71.8 +/- 12.3, nonarthritic, 91.4 +/- 11.1), but not in age or weight between the two groups. Subjects received 50 mg and then 150 mg enteric-coated racemic ketoprofen, and plasma and urine samples were collected for 24 hours. No significant differences in CL/F, area under the curve (AUC), half-life (t1/2), time to reach peak concentration (tmax), or maximum peak plasma concentration (Cmax) were found between groups or between doses, and values were similar to those previously reported in young adults. Urinary ketoprofen conjugate (S:R) ratio was 1.6 +/- .25 and 1.65 +/- .27 for arthritic and nonarthritic subjects. Greater amounts of conjugated ketoprofen enantiomers were present in the plasma of the arthritic compared with nonarthritic subjects. Renal clearance of ketoprofen conjugates exhibited stereoselectivity (R > S), and was decreased in the arthritic group. Significant changes in the kinetics of unchanged ketoprofen was not found to occur in elderly subjects in the presence or absence of rheumatic disease or moderate renal impairment.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of the route of administration on the pharmacokinetics of pirprofen enantiomers in the rat

The pharmacokinetics of the enantiomers of the non-steroidal anti-inflammatory drug pirprofen were studied in male Sprague-Dawley rats after oral and intravenous (iv) doses of the racemate. No significant differences were detected between the enantiomers after oral or iv dosing in t1/2, Vd, or sigma Xu. However, the R:S area under the plasma concentration (AUC) ratio after oral doses (0.92 +/- 0.13) was slightly but significantly lower than after matching iv doses (1.05 +/- 0.036). The absolute bioavailability of the active S-enantiomer (78.5%) after oral doses was higher than the inactive R-enantiomer (69.3%). The plasma protein binding of both enantiomers was saturable over a fivefold range of plasma concentrations. At higher plasma concentrations, the S-enantiomer was less bound than the R-enantiomer. In an in vitro experiment using everted rat jejunum, no chiral inversion was discernible. The dependency of the AUC ratio of the enantiomers on the route of administration may be due to stereoselective first-pass metabolism.

Improved high-performance liquid chromatographic assay method for the enantiomers of ibuprofen

A rapid, inexpensive and sensitive high-performance liquid chromatographic method for the quantitation of ibuprofen enantiomers from a variety of biological fluids is reported. This method uses a commercially available internal standard and has significantly less interference from endogenous co-extracted solutes than do previously reported methods. The method involves the acid extraction of drug and internal standard [(+/-)-fenoprofen] from the biological fluid with isooctane-isopropanol (95:5) followed by evaporation and derivatization with ethylchloroformate and R-(+)-alpha-phenylethylamine. Excellent linearity was observed between the peak-area ratio and enantiomer concentration (r > 0.99) over a concentration range of 0.25-50 micrograms/ml. This method is suitable for the quantitation of ibuprofen from single-dose pharmacokinetic studies involving either rats or humans.