R-flurbiprofen: isomeric ballast or active entity of the racemic compound?

The enantioselective pharmacokinetic behaviour of the flurbiprofen enantiomers was investigated following administration of optically pure R- or S-flurbiprofen to various species. Only negligible inversion (< 5%) of flurbiprofen occurred in the rat and in man. Consequently, pharmacodynamic experiments evaluating pain and inflammation as parameters have been carried out enantioselectively for both flurbiprofen enantiomers in the rat. R-flurbiprofen, which is not an inhibitor of prostaglandin synthesis in vitro, had only marginal anti-inflammatory effects as defined by the carrageenan edema of the rat paw in contrast to the S-enantiomer. In contrast, to S-flurbiprofen, R-flurbiprofen caused only marginal mucosal damage in the GI-tract. Both enantiomers, however, were of similar potency as antinociceptive drugs in the rat Randall-Selitto assay following the injection of interleukin-1 or baker's yeast. Using the pure enantiomers of flurbiprofen it appears possible to establish a more specific drug treatment: the R-enantiomer in occasional pain, the S-enantiomer in rheumatic disorders.

Metabolic chiral inversion of 2-arylpropionates in different tumor cell lines.

The study presented aimed at investigating whether tumor cell lines in continuous culture could be used as in vitro model for inversion experiments. The effect of culture conditions on the extent of inversion was examined. Under optimized culture conditions human and rat tumor cell lines were incubated with the enantiomers of ibuprofen, ketoprofen and flurbiprofen, respectively. Similarly to the situation in man in vivo, inversion of R-ibuprofen occurred in human hepatoma cells, where no inversion of R-ketoprofen or negligible inversion of R-flurbiprofen could be observed. In contrast to R-flurbiprofen the R-enantiomers of ibuprofen and ketoprofen were substantially inverted in the rat hepatoma cells in accordance with observations in the rat in vivo.

Pure enantiomers of 2-arylpropionic acids: tools in pain research and improved drugs in rheumatology.

The mode of action of aspirinlike drugs in pain is widely referred to as inhibition of prostaglandin synthesis. Salicylic acid, however, at low doses, is an analgesic but not a potent anti-inflammatory agent. This "enigma" may be resolved by recent findings employing 2-arylpropionic acids. Pure enantiomers of these chiral drugs show a different pharmacodynamic and pharmacokinetic profile. Using pure enantiomers of flurbiprofen, ibuprofen, and ketoprofen, we could show that (1) R-enantiomers of these drugs are inverted to S-enantiomers to a different degree in different species, including humans, (2) the pharmacokinetic parameters of both pure enantiomers differ in a drug- and a species-specific manner, and (3) both enantiomers exert differential analgesic effects. It appears particularly interesting that R-flurbiprofen, for instance, which is not or only to a small extent inverted in humans and rats, is practically devoid of prostaglandin synthesis inhibition in vitro. Consequently, in line with current thinking, R-flurbiprofen is not toxic to the gastrointestinal tract and shows no anti-inflammatory effects. In contrast to current concepts, however, this enantiomer does exert analgesic activity in different models of pain and nociception. It is concluded that R-flurbiprofen and, possibly, other R-enantiomers of 2-arylpropionic acids may exert novel analgesic effects independently of peripheral prostaglandin synthesis inhibition in inflamed tissue.

Variability of inversion of (R)-flurbiprofen in different species.

The anti-inflammatory activity of 2-arylpropionic acids like flurbiprofen appears to be due to the S enantiomers only. A unique characteristic of the metabolism of this class of drugs is inversion of configuration. The present study examines whether chiral inversion occurs after administration of the optically pure flurbiprofen enantiomers to various species (i.e., dogs, guinea pigs, rats, and gerbils). Concentrations of the enantiomers in plasma were analyzed by a stereoselective high-performance liquid chromatographic assay with a chiral alpha 1-acid glycoprotein column. Pharmacokinetic parameters of the flurbiprofen enantiomers were evaluated with a two-compartment computer model. Inversion of (R)-flurbiprofen to its optical antipode occurred to a variable extent in the dog [fraction inverted (Fi) = 0.39; n = 3] and the guinea pig (Fi = 1.00; n = 3) and to a much lower extent in the rat (Fi = 0.02; n = 3) and the gerbil (Fi = 0.05; n = 3). After intravenous administration of (S)-flurbiprofen to dogs, guinea pigs, rats, and gerbils, (R)-flurbiprofen was not detected in plasma (limit of quantification was 0.05 microgram/100 microL of plasma).

Metabolic chiral inversion of 2-arylpropionates in rat H4IIE and human Hep G2 hepatoma cells. Relationship to in vivo metabolism.

The inversion of 2-arylpropionic acids (2-APAs) has been investigated in vitro using rat H4IIE and human Hep G2 hepatoma cells in continuous culture. The effect of substrate concentration (15-150 micrograms/mL), cell density (1.5-12 x 10(6) cells/dish) and serum content of the culture medium (0-20%) on inversion was examined in rat H4IIE hepatoma cells using R-ibuprofen as model compound. Increasing R-ibuprofen concentrations and decreasing serum content of the medium resulted in increased inversion whereas variation of cell density had no effect. Furthermore, rat H4IIE and human Hep G2 hepatoma cells were incubated with the individual enantiomers of ibuprofen, ketoprofen and flurbiprofen under optimized culture conditions (serum-free culture medium). The elimination rate constants (kel) and fractions inverted (Fi) were determined. Although inversion occurred slowly in the tumor cells and thus long incubation periods (120 hr) were required, the hepatoma cells were nevertheless able to mimic qualitatively the species and substance specificity of inversion of 2-APAs as observed in vivo.

Stereoselective high-performance liquid chromatographic determination of flurbiprofen in human plasma.

An enantioselective high-performance liquid chromatographic assay for the quantitation of the enantiomers of flurbiprofen in human plasma is described. The procedure involved extraction of flurbiprofen from acidified plasma into hexane-diethyl ether (8:2, v/v). Stereoselective separation was achieved with a prepacked alpha 1-acid glycoprotein column without any derivatization procedure. A second assay using a conventional reversed-phase column to determine racemic flurbiprofen is also described. The detection wavelength was set at 246 nm. The limit of quantification was found to be 50 ng/ml for both assays. The method was demonstrated to be sufficiently sensitive for stereoselective pharmacokinetic studies of flurbiprofen.

Differential analgesic effects of aspirin-like drugs.

Tissue damage, including that due to surgical manipulation, results in 2 distinct but connected changes in the pain perception pathway. Firstly, cells disintegrate at the site of tissue damage and release mediators, including prostaglandins. These mediators transform fine nerve endings, particularly high-threshold mechanoceptors, into nociceptors. In other words, fine nerve endings that are not normally activated by mechanical pressure or temperature changes become very sensitive and are depolarised after minor mechanical or thermal changes. Secondly, in the central nervous system (CNS) and, particularly, in the dorsal horn of the spinal cord, reflex activity is increased, metabolic activity of the neuronal cells is enhanced and, chronically, major rearrangements of mediator production and electrical activity of the dorsal horn cells may be observed. Both types of change contribute to the well known phenomenon of hyperalgesia, which is regularly observed in connection with tissue damage, including that produced by surgical manipulation. It has been shown that aspirin-like drugs reduce the enhanced nociceptor activity in damaged tissue, probably as a result of prostaglandin synthesis inhibition. Recently, there have been indications that these drugs may have an additional mechanism of action in the spinal cord or higher parts of the CNS. Using the pure enantiomers of flurbiprofen in pharmacodynamic experiments in the rat, we have observed that the R- and S-enantiomers may exert differential analgesic effects. The R-enantiomer, which does not inhibit cyclo-oxygenase in vitro, was almost as effective as the S-enantiomer, which does inhibit prostaglandin synthesis in different models of pain and nociception.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereoselective high-performance liquid chromatographic determination of the enantiomers of ketamine and norketamine in plasma.

An enantioselective high-performance liquid chromatographic assay for the quantitation of the enantiomers of ketamine and its major metabolite norketamine in human plasma is described (assay I). The procedure involved extraction of the compounds from alkalized plasma into cyclohexane. Stereoselective separation was achieved with a prepacked alpha 1-acid glycoprotein column without any derivatization procedure. A second assay using a conventional reversed-phase column to determine total (racemic) ketamine and norketamine is also described. Because of interfering plasma peaks (assay II) the cyclohexane solution was reextracted into 1 M hydrochloric acid. The detection wavelength was 215 nm for all substances. The limit of quantification of the method was ca. 40 ng/ml in plasma. The assays were sensitive and reproducible. The method was demonstrated to be sensitive for stereoselective pharmacokinetic studies of ketamine after clinical doses.

Aspirin-like drugs may block pain independently of prostaglandin synthesis inhibition.

Using flurbiprofen, a chiral anti-inflammatory and analgesic 2-arylpropionic acid derivative, the enantiomers of which are not converted to each other (less than 5%) in rats or man, we obtained evidence that prostaglandin synthesis inhibition is primarily mediating the anti-inflammatory activity but prostaglandin synthesis independent mechanisms contribute to the analgesic effects. Thus, the S-form inhibited prostaglandin synthesis, inflammation and nociception in rats. The R-form had much less effect on prostaglandin synthesis and did not affect inflammation. It did, however, block nociception in rats almost as potently as the S-form. S-flurbiprofen, in contrast to the R-form, was clearly ulcerogenic in the gastrointestinal mucosa. These results indicate additional molecular mechanisms of analgesia and suggest the use of R-arylpropionic acids as analgesics.

Stereoselective high-performance liquid chromatographic determination of ketoprofen, ibuprofen and fenoprofen in plasma using a chiral alpha 1-acid glycoprotein column.

The effect of mobile phase composition, pH and temperature on the chiral resolution and retention of some 2-arylpropionic acids using the chiral alpha 1-acid glycoprotein column EnantioPac is described. Furthermore, a direct stereoselective high-performance liquid chromatographic assay to determine the enantiomers of ketoprofen, ibuprofen and fenoprofen in plasma is presented. Detection was at 260, 220 and 220 nm for ketoprofen, ibuprofen and fenoprofen, respectively. The limit of detection was 0.1 micrograms/ml for the enantiomers of ketoprofen and ibuprofen, and 0.25 micrograms/ml for the enantiomers of fenoprofen. The method was demonstrated to be applicable for stereoselective pharmacokinetic studies of ketoprofen, ibuprofen and fenoprofen after administration under clinical conditions.