High-performance liquid chromatographic assay of ketoprofen enantiomers in human plasma and urine

Analytical chiral separation of a new quinolone compound in biological fluids by high-performance liquid chromatography

Two methods for the separation of a new racemic quinolone compound, temafloxacin (TMFX), in biological fluids by high-performance liquid chromatography (HPLC) were studied. The first method was coupling of TMFX to S-(-)-N-1-(2-naphthyl sulfonyl)-2-pyrrolidine carbonylchloride (L-NSPC). The diastereomeric derivatives were separated on a silica gel column. The second method was separation on a chiral stationary phase with an ovomucoid conjugated to aminopropyl silica gel. Two enantiospecific methods gave a satisfactory result concerning both accuracy and precision, and the second method was superior to the first one for chromatographic separation. Furthermore, the pharmacokinetics of the enantiomers after oral administration of racemic TMFX to healthy volunteers was investigated by the second method.

Influence of formulation on the pharmacokinetics and bioavailability of racemic ketoprofen in horses

The bioavailability of S(+) and R(-) ketoprofen (KTP) in six horses was investigated after oral administration of the racemic (rac) mixture. Two oral formulations were studied, an oil-based paste containing micronised rac-KTP and powder from the same source in hard gelatin capsules, each at a dose rate of 2.2 mg/kg. For the oil-based paste two feeding schedules were used; horses were either allowed free access to food or access to food was restricted for 4 h before and 5 h after dosing. The drug in hard gelatin capsules was administered to horses with restricted access to food. After intravenous administration of rac-KTP, S(+) enantiomer concentrations exceeded those of the R(-) enantiomer. For S(+) and R(-)KTP, respectively, pharmacokinetic parameters were, t1/2 beta 0.99 +/- 0.14 h, 0.70 +/- 0.13 h; ClB 0.56 +/- 0.09, 0.92 +/- 0.20 L/h/kg; Vd(ss) 0.53 +/- 0.11, 0.61 +/- 0.10 L/kg. Following oral administration of rac-KTP as the oil-based paste to horses with free access to food, there were no detectable concentrations in plasma in three animals at any sampling time, while a fourth animal showed very low concentrations at two sampling times only. In the two remaining horses very low but detectable concentrations were present for 5 h. In the horses with restricted access to food, rac-KTP paste administration produced higher concentrations in plasma. However, bioavailability was very low, 2.67 +/- 0.43 and 5.75 +/- 1.48% for R(-) and S(+)KTP, respectively. When administered as pure drug substance in hard gelatin capsules, absorption of KTP was fairly rapid, but incomplete. Bioavailability was 50.55 +/- 10.95 and 54.17 +/- 9.9% for R(-) and S(+)KTP, respectively. This study demonstrates that rac-KTP had a modest bioavailability when administered as a micronised powder in hard gelatin capsules to horses with restricted access to food. When powder from the same source was administered as an oil-based paste, it was for practical purposes not bioavailable, regardless on the feeding schedule.

Pharmacokinetics and pharmacodynamics of ketoprofen in calves applying PK/PD modelling

The pharmacokinetics (PK) and pharmacodynamics (PD) of ketoprofen (KTP) were studied in calves following intravenous administration of the drug racemate at a dose rate of 3 mg/kg. To evaluate the anti-inflammatory properties of KTP, a model of acute inflammation, consisting of surgically implanted subcutaneous tissue cages stimulated by intracaveal injection of carrageenan, was used. No differences were observed between disposition curves of KTP enantiomers in plasma, exudate or transudate. This indicates that in calves KTP pharmacokinetics is not enantioselective. S(+)- and R(-)- KTP each had a short elimination half-life (t1/2 beta) of 0.42 +/- 0.08 h and 0.42 +/- 0.09 h, respectively. The volume of distribution (Vd) was low, values of 0.20 +/- 0.06 L/kg and 0.22 +/- 0.06 L/kg being obtained for R(-) and S(+)KTP, respectively. Body clearance (ClB) was high, correlating with the short elimination half-life, 0.33 +/- 0.03 L/kg/h [R(-)KTP] and 0.32 +/- 0.04 L/kg/h [S(+)-KTP]. KTP pharmacodynamics was evaluated by determining the effects on serum thromboxane (TxB2), exudate prostaglandin (PGE2), leukotriene (LTB4) and beta-glucuronidase (beta-glu) and bradykinin (BK)-induced oedematous swelling. Effect-concentration inter-relationships were analysed by PK/PD modelling. KTP did not affect exudate LTB4, but inhibition of the other variables was statistically significant. The mean EC50 values for inhibition of serum TxB2, exudate PGE2 and beta-glu and BK-induced swelling were 0.118, 0.086, 0.06 and 0.00029 microgram/mL, respectively. These data indicate that KTP exerted an inhibitory action, not only as expected, on eicosanoid (TxB2 and PGE2) synthesis but also on exudate beta-glu and BK-induced oedema. The EC50 values for these actions indicate that they are likely to contribute to the overall anti-inflammatory effects of KTP in calves. However, claims that KTP inhibits 5-lipoxygenase and thereby blocks the production of inflammatory mediators such as LTB4 were not substantiated. PK/PD modelling has proved to be a useful tool for analysing the in vivo pharmacodynamics of KTP and for providing new approaches to elucidating its mechanism(s) of action.

Stereoselective disposition of ibuprofen enantiomers in human cerebrospinal fluid

Since both (R)- and (S)-enantiomers of ibuprofen may act on the central nervous system, we investigated their plasma and cerebrospinal fluid (CSF) concentrations in 46 patients with nerve-root compression pain requiring a lumbar puncture. Each patient received an oral dose of 800 mg rac-ibuprofen. A single blood and CSF sample was drawn concomitantly from each patient at intervals between 30 min and 8 h after dosing. Both isomers peaked later in the CSF (3 h) than in the plasma (1.5 h). Their CSF concentrations became higher than their concurrent free plasma concentrations after 90 min. The estimated elimination half-lives of (R)- and (S)-ibuprofen were 1.7 h and 2.5 h in plasma and 3.9 h and 7.9 h in CSF, respectively. The AUCCSF/AUCplasma ratios (0, 8 h) were 0.009 and 0.015 for the (R)- and (S)-forms, respectively.

Comparison of the anti-inflammatory actions of flunixin and ketoprofen in horses applying PK/PD modelling

A comparative study in horses of the pharmacokinetics (PK) and pharmacodynamics (PD) of 2 extensively used nonsteroidal anti-inflammatory drugs (NSAIDs), flunixin (FXN) and ketoprofen (KTP), was carried out applying PK/PD modelling. To evaluate the anti-inflammatory properties of these drugs a model of acute inflammation, comprising surgically implanted subcutaneous tissue cages stimulated by intracaveal injection of carrageenan, was used. FXN elimination half-life (T1/2 beta) in plasma was 3.37 +/- 1.09 h. However, in exudate a much longer T1/2 beta was obtained (15.99 +/- 3.80 h). Apparent volume of distribution (Vdarea) for FXN was 0.317 +/- 0.126 l/kg and body clearance (ClB) was 0.058 +/- 0.004 l/kg/h. KTP displayed enantioselective pharmacokinetics, the S(+) enantiomer being predominant in plasma, exudate and transudate. T1/2 beta values for R(-) and S(+)KTP were, respectively, 1.09 +/- 0.19 h and 1.51 +/- 0.45 h (plasma) and 19.73 +/- 2.72 h and 22.64 +/- 4.34 h (exudate), respectively. R(-)KTP was cleared more rapidly than the S(+) enantiomer. ClB values were 0.277 +/- 0.035 l/kg/h and 0.202 +/- 0.022 l/kg/h, respectively. FXN and KTP pharmacodynamics was evaluated by determining their inhibitory effects on serum thromboxane (Tx)B2, exudate prostaglandin (PG)E2, leukotriene (LT)B4 and beta-glucuronidase (beta-glu) and intradermal bradykinin-induced swelling. Both drugs produced marked inhibition of serum TxB2 synthesis for up to 24 h, with no significant differences between the drugs. FXN was a more potent inhibitor of exudate PGE2, the EC50 for FXN being lower (P < 0.01) than that for KTP (0.019 +/- 0.010 microgram/ml and 0.057 +/- 0.009 microgram/ml, respectively). Neither drug had any effect on exudate LTB4 concentration. Differences between the 2 drugs were observed for the inhibition of beta-glu, the Emax for KTP being higher (P < 0.01) than for FXN. However, no differences were observed in other PD parameters. Both FXN and KTP inhibited bradykinin-induced swelling. Differences between the drugs were obtained for Emax, which was greater for FXN (P < 0.01) than for KTP. Equilibration half-life (T1/2Ke0) also differed, being much longer (P < 0.01) for FXN than for KTP. PK/PD modelling proved to be a useful and novel analytical technique for studying the pharmacodynamics of NSAIDs, with the advantage over classical in vitro methods that it provides data in the whole animal. By quantifying action-concentration interrelationships through PK-PD modelling, it is possible to shed light on molecular mechanisms of drug action, and establish probable differences in mechanisms of action between structurally similar drugs.(ABSTRACT TRUNCATED AT 400 WORDS)

Stereospecific high-performance liquid chromatographic assay of ketoprofen in human plasma and urine

A high-performance liquid chromatographic (HPLC) assay suitable for the analysis of the enantiomers of ketoprofen (KT), a 2-arylpropionic acid (2-APA) non-steroidal antiinflammatory drug (NSAID), in plasma and urine was developed. Following the addition of racemic fenoprofen as internal standard (I.S.), plasma containing the KT enantiomers and I.S. was extracted by liquid-liquid extraction at an acidic pH. After evaporation of the organic layer, the drug and I.S. were reconstituted in mobile phase and injected into the HPLC system. The enantiomers were separated at ambient temperature on a commercially available 250 x 4.6 mm amylose carbamate-packed chiral column (Chiralpak AD) column with hexane-isopropyl alcohol-trifluoroacetic acid (80:19.9:0.1, v/v/v) as the mobile phase pumped at 1.0 ml/min. The enantiomers of KT were quantified by ultraviolet detection with the wavelength set at 254 nm. The assay described allows for the direct quantitation of KT enantiomers without pre-column derivatization, and is suitable for clinical studies of KT enantiomers in human plasma and urine after administration of therapeutic doses.

Comparative metabolism of R(-)-fenoprofen in rats and sheep

The chiral inversion of 2-arylpropionic acids occurs in many species. It is a unique reaction specific to this group of drugs. In this study R-(-)-fenoprofen (R-(-)-FPF) was used as a model compound to investigate metabolic chiral inversion in sheep in vivo and in vitro to compare the data with the results obtained in rats. Metabolic inversion in sheep was 80%. The apparent mean values of Km and Vmax of thioester formation were: 392 microM and 2.08 nmol/min/mg in sheep and 500 microM and 22 nmol/min/mg in rats. For hydroxylation, the apparent mean values were Vmax: 0.02 nmol/min/mg in rats and 0.01 nmol/min/mg in sheep. There was no correlation between in vitro thioesterification and in vivo chiral inversion in sheep as compared to rats. In sheep most of the thioester formed underwent inversion (80%) while in rats, where in vitro thioesterification was greater, in vivo inversion was less (42%). In consequence, in rats other metabolic pathways for R(-)-FPF-CoA, such as incorporation into triacylglycerols and conjugation with amino acids, may be quantitatively more important.

Pharmacokinetics and pharmacodynamics of ketoprofen enantiomers in calves

The pharmacokinetics (PK) and pharmacodynamics (PD) of (S)- and (R)-ketoprofen (KTP) enantiomers were studied in calves after intravenous administration of each enantiomer at a dose of 1.5 mg/kg. Pharmacodynamic properties were evaluated using a model of acute inflammation, comprising subcutaneously implanted tissue cages stimulated by intracaveal injection of carrageenan. Chiral inversion of (R)-KTP to the (S)-antipode occurred. The R:S ratio in plasma was 33:1 5 min after administration, decreasing to 1:1 at 8 h. The calculated extent of inversion was 31 +/- 7%. The R:S ratio in inflammatory exudate was of the order 3:1 at all the sampling times and the ratio in transudate was approximately 2:1 for 6 h, declining to 1:1 at 30 h. Only (S)-KTP was detected in biological fluids after administration of this enantiomer. Elimination half-life was longer for the (S) (2.19 h) than the (R)-enantiomer (1.30 h) and volume of distribution was also somewhat higher for the (S)-enantiomer. Body clearance values were 0.119 l/kg/h for (S)-KTP and 0.151 l/kg/h for the (R)-antipode. For (R)-KTP effects obtained were considered as a hybrid, since they potentially reflect the actions of both enantiomers. Concentrations of LTB4 and the cytokines interleukin-1, interleukin-6, and tumor necrosis factor alpha, in exudate were not significantly affected by either (R)- or (S)-KTP treatments. Inhibition of ex vivo thromboxane B2 (TxB2) synthesis, exudate prostaglandin E2 (PGE2) synthesis, beta-glucuronidase release (beta-glu), and bradykinin-induced skin swelling was significant in both treated groups. PK/PD modelling was applied to the (S)-KTP treatment only. EC50 values for inhibition of serum TxB2, exudate PGE2 and beta-glu and BK-induced swelling were 0.047, 0.042, 0.101, and 0.038 microgram/ml, respectively. It is concluded that the low EC50 values for inhibition of TxB2 and PGE2 by (S)-KTP are likely to explain the effects produced by (R)-KTP administration, since concentrations of (S)-KTP in exudate of these calves following chiral inversion were at least 5 times higher than the EC50 at all sampling times. The data for beta-glu and bradykinin-induced swelling inhibition indicate possible inhibitory actions of (R)-KTP as well as (S)-KTP.

Stereospecific pharmacodynamics and pharmacokinetics of carprofen in the dog

The non-steroidal anti-inflammatory drug (NSAID) carprofen (CPF) contains a single chiral centre. It was administered orally to Beagle dogs as a racemate (rac-CPF) at a dose of 4 mg per kg body weight and as individual (-)(R) and (+)(S) enantiomers at 2 mg per kg body weight. Each of the enantiomers achieved similar plasma bioavailability following administration as the racemate as they did following their separate administration. Only the administered enantiomers were detectable when the drug was given in the (-)(R) or (+)(S) form, indicating that chiral inversion did not occur in either direction. Higher plasma concentrations of the (-)(R) (Cmax 18 micrograms/ml, AUC0-24 118 micrograms h/ml) than the (+)(S) (Cmax 14 micrograms/ml, AUC0-24 67 micrograms h/ml) enantiomer were achieved following administration of the racemate. Both enantiomers distributed into peripheral subcutaneous tissue cage fluids, but Cmax and AUC values were lower for both transudate (non-stimulated tissue cage fluid) and exudate (induced by the intracaveal administration of the irritant carrageenan) than for plasma. Drug concentrations in transudate and exudate were similar, as indicated by Cmax and AUC values, although CPF penetrated more rapidly into exudate than into transudate. Neither rac-CPF nor either enantiomer inhibited thromboxane B2 (T x B2) generation by platelets in clotting blood (serum T x B2), or prostaglandin E2 (PGE2) and 12-hydroxyeicosatetraenoic acid (12-HETE) synthesis in inflammatory exudate.(ABSTRACT TRUNCATED AT 250 WORDS)

Labeling of free carboxyl groups

The latest trends in the labeling of free carboxyl groups for high-performance liquid chromatography are reviewed. The labeling reagents for fluorescence detection are mainly discussed according to their reaction type (or functional group). Attention is also paid to the reagents used for ultraviolet detection and for enantiomeric separation. The reactivity and sensitivity of the reagents used for the labeling of carboxylic acids are described.

Enantiospecific determination of ibuprofen in rat plasma using chiral fluorescence derivatization reagent, (-)-2-[4-(1-aminoethyl)phenyl]-6- methoxybenzoxazole

A highly sensitive and reversed-phase high-performance liquid chromatographic method for the determination of the enantiomeric composition of ibuprofen in rat plasma is described. The method is based on the resolution of the diastereomeric amides formed on reaction of the ibuprofen enantiomers with (-)-2-[4-(1-aminoethyl)phenyl]-6-methoxybenzoxazole ((-)-APMB) in the presence of 2,2'-dipyridyl disulphide (DPDS) and triphenylphosphine (TPP) in dichloromethane. The reaction mixture was allowed to stand at room temperature for 5 min, and the reaction was completed by evaporation with a stream of nitrogen at 40 degrees C. The minimum quantifiable concentrations were 0.2 microgram/mL and 0.4 microgram/mL for S-ibuprofen and R-ibuprofen, respectively, in a 10 microL injection volume. The method was applied to the determination of enantiomeric ibuprofen in plasma after oral administration to rats.

Enantiomeric separation of amide derivatives of some 2-arylpropionic acids by HPLC on a cellulose-based chiral stationary phase

A reversed phase high-performance liquid chromatographic method has been developed for the determination of the R- and S-enantiomers of ibuprofen, flurbiprofen, ketoprofen and tiaprofenic acid. Separation has been achieved using a tris(4-methylbenzoate)cellulose phase after derivatization into their amides. Flurbiprofen could also be partially resolved into its enantiomers without prior derivatization.

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)

Limited extent of stereochemical conversion of chiral non-steroidal anti-inflammatory drugs induced by derivatization methods employing ethyl chloroformate

A potential problem with chiral derivatization is the possibility of stereochemical conversion during the derivatization reaction. This possibility has been examined using the non-steroidal anti-inflammatory drugs ibuprofen, ketoprofen, etodolac and flurbiprofen. To avoid possible interference from stereochemical impurities, male Sprague-Dawley rats were dosed intraperitoneally with the S enantiomer (100 mg/kg) of each drug and the R enantiomer of etodolac. Blood samples were taken 4 h afterwards. The plasma samples were analyzed using published stereospecific methods involving chiral derivatization with ethyl chloroformate followed by either R-(+)-alpha-phenylethylamine or L-leucinamide. For all the drugs examined, the percentage of formation of the antipode was between 1.0 and 5.8%. In vitro studies of the R and S enantiomers demonstrate that the apparent extent of conversion is inversely related to the concentration of ethyl chloroformate present during the derivatization reaction for ibuprofen, ketoprofen and flurbiprofen but not for etodolac. However, both the R and S enantiomers appear to be inverted to the same extent in the presence of ethyl chloroformate. These results suggest that the degree of stereochemical conversion induced by these assay procedures is small and would not contribute significantly to analytical error in the absence of a large difference in concentrations of the enantiomers.

Stereoselective protein binding of ketoprofen: effect of albumin concentration and of the biological system

Equilibrium dialysis was used to study in vitro the enantioselective binding of R, S, and racemic ketoprofen at physiological pH and temperature in human serum albumin (HSA) (1, 20, and 40 g/liter) and in plasma. The binding of enantiomers in a racemic mixture was studied to see the effect of each isomer on the other's interaction with the protein. The free fractions were determined by high-performance liquid chromatography. The binding of ketoprofen enantiomers to albumin was enantioselective, depending on both drug and protein concentrations. Enantioselectivity was observed in plasma too but was the opposite of that in HSA at 40 g/liter. The percentage of each isomer unbound was higher in the racemic mixture than with the isomer alone. The displacement of probes specific for HSA sites I and II, studied by spectrofluorimetry, suggests that all three preparations of ketoprofen are bound mainly to site I and secondarily to site II.

Enantiospecific gas chromatographic-mass spectrometric procedure for the determination of ketoprofen and ibuprofen in synovial fluid and plasma: application to protein binding studies

A method for the enantiospecific quantitation of two commonly prescribed non-steroidal anti-inflammatory drugs (ketoprofen and ibuprofen) is described. The method involves formation of a mixed anhydride of the drug with ethylchloroformate and subsequent conversion to an amide by reaction with optically active amphetamine. The subsequently formed diastereomers are separated by gas chromatography-mass spectrometry using selected-ion monitoring. The assay is capable of quantifying ketoprofen (2 ng/ml) and ibuprofen (3 ng/ml) enantiomers from a 200-microliters sample of synovial fluid or plasma and is particularly suitable for protein binding studies.

Identification of a benzhydrolic metabolite of ketoprofen in horses by gas chromatography-mass spectrometry and high-performance liquid chromatography

A benzhydrolic metabolite of ketoprofen, formed by reduction of the keto group of the drug, has been identified by gas chromatography-mass spectrometry in equine plasma and urine. After partial synthesis, its structure has been confirmed by UV, IR and 1H NMR spectroscopy. The kinetics of ketoprofen and this metabolite have been monitored in plasma by high-performance liquid chromatography. The two products were quantified in plasma up to 4 and 3 h, respectively, and were detected in urine up to 72 and 24 h, respectively, after a single intravenous administration to horses at the dose of 2.2 mg/kg. Simultaneous detection of both compounds increases the reliability of antidoping control analysis.

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.

Chiral separation by high performance liquid chromatography. I. Review on indirect separation of enantiomers as diastereomeric derivatives using ultraviolet, fluorescence and electrochemical detection

The increased attention on the therapeutic implications of stereoisomerism has provided an impetus for the development of analytical methods for enantiomeric separation. The indirect method of separation of enantiomers as diastereomers using high performance liquid chromatography (HPLC) has emerged as an efficient and versatile approach. This is due mainly to the availability of numerous chiral derivatization reagents (CDRs). This article reviews CDRs useful for the development of an indirect HPLC method using ultraviolet, fluorescence and electrochemical detection. In addition, factors crucial for the development of the indirect method are discussed.

Stereospecific high-performance liquid chromatographic assay of pirprofen enantiomers in rat plasma and urine

A stereospecific high-performance liquid chromatographic method was developed for the assay of pirprofen enantiomers in rat plasma and urine. Following addition of internal standard (ketoprofen) and acidifier (L-ascorbic acid) to biological fluids, pirprofen was extracted into an isopropanol-isooctane (5:95) mixture. Diastereomers of pirprofen enantiomers, which were formed using L-leucinamide, were separated on a reversed-phase column with ultraviolet detection at 275 nm using 0.06 M KH2PO4-acetonitrile-triethylamine (64:36:0.1) as mobile phase. The limit of quantitation was 0.1 microgram/ml for each enantiomer, based on 100 microliters of rat plasma. No spontaneous oxidation of pirprofen to its pyrrole metabolite occurred during sample preparation and analysis. In three female rats which were dosed with 10 mg/kg racemic pirprofen orally, plasma concentrations of the enantiomers could be followed for 24 h. Pirprofen enantiomers in plasma were virtually unconjugated, and negligible concentrations of pyrrole metabolites were observed. Less than 10% of the total dose was recovered in urine as intact drug and its glucuroconjugates. The assay was found suitable for the study of the pharmacokinetics of pirprofen enantiomers in the rat.

Simultaneous determination of (R)- and (S)-naproxen and (R)- and (S)-6-O-desmethylnaproxen by high-performance liquid chromatography on a Chiral-AGP column

A high-performance liquid chromatographic method for the simultaneous determination of both enantiomers of naproxen and its metabolite 6-O-desmethylnaproxen has been developed. The separation is performed on a column containing alpha 1-acid glycoprotein as the chiral selector. The method has been used for the determination of the enantiomeric purity of the drug substance and the metabolite, and for the simultaneous determination of all four compounds in biological fluids.

Enantiospecific analysis of ketoprofen in plasma by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) assay for the determination of the R- and S-enantiomers of ketoprofen is described. Facile ketoprofen extraction from plasma and derivatization to the diastereomeric S-1-phenylethylamides was followed by normal-phase HPLC. The ketoprofen diastereomeric amides eluted within 8 min. The limit of quantification of the assay was 0.15 mg/l of each enantiomer (signal-to-noise ratio = 5).

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.

Simultaneous determination of ketoprofen enantiomers and probenecid in plasma and urine by high-performance liquid chromatography

A rapid, sensitive, stereospecific reversed-phase high-performance liquid chromatographic method was developed for simultaneous quantitation of ketoprofen enantiomers, probenecid and their conjugates in biological fluids. Following addition of the internal standard, indoprofen, the constituents were extracted into isooctane-isopropanol (95:5), water-washed, extracted with chloroform, then evaporated and the residue sequentially derivatized with ethyl chloroformate and L-leucinamide hydrochloride. The formed diastereomers were chromatographed on a reversed-phase column with a mobile phase of 0.06 M KH2PO4-acetonitrile-triethylamine (65:35:0.1) at a flow-rate of 1 ml/min and a detection wavelength of 275 nm. The minimum quantifiable concentration was 0.5 micrograms/ml in 100 microliters of rat plasma and urine samples. The intra- and inter-day coefficients of variation for this method are less than 10%. The assay is successfully applied to a pharmacokinetic study. The simultaneous analysis of probenecid with several other non-steroidal anti-inflammatory drugs was also successful.

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.

Pharmacological aspects of chiral nonsteroidal anti-inflammatory drugs

Most NSAIDs are chiral molecules: they exist under 2 configurations of non-superimposable mirror images which are termed enantiomers or optical isomers or optical antipodes. Direct or indirect (resolution) methods are used to separate this equal mixture of compounds. Some of the enantiomers of the NSAIDs are able to undergo chiral inversion from the inactive R(-) to the active S(+) form. The pharmacokinetics in terms of absorption, distribution, metabolism, protein binding and elimination may be different for the 2 enantiomers, leading to interindividual variability in clinical response and drug toxicity.

Pharmacokinetics of ketoprofen enantiomers in cholecystectomy patients: influence of probenecid

Ketoprofen (KT), a 2-arylpropionic acid nonsteroidal antiinflammatory drug, is administered as a racemate. Previous reports suggest stereoselective biliary excretion of KT enantiomers. This hypothesis was tested by administering 50 mg racemic KT to five patients who required bile drainage following cholecystectomy surgery. Subsequently, to study the influence of probenecid (PB), an inhibitor of KT renal elimination, on the biliary excretion, 1000 mg PB was administered 1.5 h before KT to the same patients. The unchanged and conjugated (as glucuronides) KT enantiomers were measured in plasma, urine and bile. In general, KT enantiomers had different plasma concentration-time curves. As compared to normal subjects, these patients had comparable AUCs and shorter t1/2s. Biliary concentrations of conjugated S-KT were greater than R-KT. Nevertheless, the total cumulative biliary excretion of conjugated KT did not exceed 2% of the dose ruling out this pathway as a significant route of KT elimination. There was a positive and significant correlation between the cumulative urinary excretion of conjugated KT enantiomers and creatinine clearance. Although PB did not influence the pattern of stereoselectivity of KT, it increased AUC and prolonged t1/2 of the enantiomers. While reducing cumulative urinary excretion, PB increased total biliary elimination of conjugated KT enantiomers. This, however, did not totally compensate for the reduced urinary excretion. It is suggested that the impaired conjugation of KT caused by PB administration may result in the augmentation of other, otherwise minor, metabolic pathways.

Application of a stereospecific high-performance liquid chromatography assay to a pharmacokinetic study of etodolac enantiomers in humans

An HPLC assay suitable for pharmacokinetic analysis of enantiomers of etodolac [(+/-)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b] indole-1-acetic acid] was developed. Following addition of internal standard (IS), (+/-)-2-(4-benzoylphenyl)butyric acid, the constituents were extracted from the specimen into a mixture of isooctane:isopropanol (95:5). The organic layer was evaporated and the drug and IS were sequentially derivatized with ethyl chloroformate and iota(-)-alpha-phenylethylamine. The diastereoisomers thus formed were extracted and chromatographed on a normal-phase column, with a mobile phase consisting of hexane:ethyl acetate:isopropanol (85:15:0.2) at a flow rate of 2 mL/min. The etodolac diastereoisomers were separated with a resolution factor of 6.4 and detected at a wavelength of 280 nm. Excellent linear relationships were found between the peak area ratios (etodolac:IS) and the plasma and urine concentrations (0.2-20 mg/L), with intra- and interday variations of less than 10.1%. The assay was applied to a preliminary pharmacokinetic study following seven repeated oral administrations of 200 mg/12 h of racemic etodolac to two healthy subjects. The plasma concentrations of the active S-(+)-enantiomer were considerably less than those of the inactive antipode (AUC S:R, 2.5:30.9 mg.L-1.h-1) due to a greater volume of distribution of the latter (S, 101 and 135 L versus R, 24 and 17 L). Considerable concentrations of conjugated enantiomers were also found in plasma (AUC conjugated: intact: S, 1.1; R, 0.23).

Rapid and sensitive high-performance liquid chromatographic assay of tiaprofenic acid enantiomers in human plasma and urine

A sensitive stereospecific high-performance liquid chromatographic assay of tiaprofenic acid (TA) enantiomers in human plasma and urine was developed. The biological specimens are acidified, and the drug and internal standard, (+/-)-2-(4-benzoylphenyl)butyric acid, extracted with an isooctane-isopropanol (95:5) mixture (plasma) or chloroform (urine), followed by sequential reaction of the enantiomers with trichloroethyl chloroformate and L-leucinamide. The reactions were complete at ambient temperature in less than 3 min. The diastereoisomers of TA and internal standard were then extracted into chloroform. The organic layer was evaporated, and the reconstituted residue chromatographed at ambient temperature on a C18 reversed-phase column with a mobile phase consisting of 0.06 M monopotassium phosphate-acetonitrile-triethylamine (65:35:0.02) at a flow-rate of 1 ml/min. The TA diastereoisomers were detected at 310 nm, free of interfering peaks, with a resolution factor of 2.1. Within the examined plasma and urine enantiomeric concentration ranges of 0.2-20 and 10-100 mg/l, respectively, an excellent linear relationship was obtained between the peak-area ratios and the corresponding concentrations. The assay was reproducible and sufficiently accurate to be applied to the stereoselective pharmacokinetic analysis of TA enantiomers in plasma and urine following administration of therapeutic doses of the drug.

Pharmacokinetics of ketoprofen enantiomers in young and elderly arthritic patients following single and multiple doses

Ketoprofen (KT), a chiral nonsteroidal anti-inflammatory drug (NSAID), is marketed and used as a racemic mixture. In healthy volunteers, negligible differences have been reported between the plasma time courses of KT enantiomers. Using a stereospecific high-performance liquid chromatographic (HPLC) assay measuring (R)- and (S)-KT in plasma and urine, pharmacokinetics of the enantiomers following single (50 mg) and then multiple (50 mg every 6 h for 3 d) doses were delineated in nine young and nine elderly arthritic patients. There were no significant differences between pharmacokinetic indices calculated after single and multiple doses, or between the two groups. In plasma, there were no significant differences between intact enantiomers in either patient group. However, significantly more conjugated (S)-KT was found in elderly patient plasma. Similar to findings in healthy volunteers, elimination of conjugated KT in both patient groups was more extensive for the (S)-, as compared with the (R)-isomer. It is suggested that age-dependent impaired elimination of conjugated (S)-KT, along with preferential biliary excretion of conjugated (R)-KT, is responsible for these observations.

Pharmacokinetics of ketoprofen enantiomers in healthy subjects following single and multiple doses

Ketoprofen (KT; m-benzoylhydratropic acid), a 2-arylpropionic acid (2-APA) nonsteroidal anti-inflammatory drug (NSAID), is marketed and used as a racemic mixture. Although generally the activity of 2-APAs is suggested to be mainly due to the S-enantiomer, information on KT pharmacokinetics is based on measurement of total concentrations of S- and R-enantiomers. In this work, using a crossover fashion, the pharmacokinetics of KT enantiomers following single (50 mg, po) and then multiple (50 mg, q6h for 3 d) doses were delineated in eight healthy subjects. A sensitive stereospecific HPLC assay was used to measure KT enantiomers in plasma and urine, and conjugated KT enantiomers in urine. There were no significant differences between the pharmacokinetic indices calculated after single and multiple administration of KT. In plasma, small but significant differences were found between concentrations of the enantiomers (mean S:R ratios of 0.81 +/- 0.19 after single and 0.87 +/- 0.11 after repeated doses). Negligible amounts of unchanged KT enantiomers were found in urine. More than 80% of the given doses was found in urine as conjugated S- and R-KT, the predominant enantiomer being S-KT (mean S:R ratios of 1.19 +/- 0.05 after single and 1.17 +/- 0.05 after repeated doses). No significant difference between the elimination t1/2 of the enantiomers was observed. It is suggested that stereoselective conjugation followed by preferential biliary excretion of the conjugated R-KT enantiomer is responsible for the observed stereoselectivity in the pharmacokinetics of the drug.