Enantioselective pharmacodynamics and pharmacokinetics of chiral non-steroidal anti-inflammatory drugs

Engineering the promiscuous racemase activity of an arylmalonate decarboxylase

Variant G74C of arylmalonate decarboxylase (AMDase) from Bordatella bronchoseptica has a unique racemising activity towards profens. By protein engineering, variant G74C/V43A with a 20-fold shift towards promiscuous racemisation was obtained, based on a reduced activity in the decarboxylation reaction and a two-fold increase in the racemisation activity. The mutant showed an extended substrate range, with a 30-fold increase in the reaction rate towards ketoprofen. Molecular dynamics simulations and the substrate profile of the racemase indicate that the steric and polar effects of the substrate structure play a more dominant role on catalysis than mere kinetic α-proton acidity. The observation that the conversion of β,γ-unsaturated carboxylic acids does not lead to a rearrangement to form their α,β isomers indicates a concerted rather than a stepwise mechanism. Interestingly, a substrate bearing a nitro group instead of the carboxylic acid group on the α-carbon atom was also converted by the racemase.

Directed evolution of an enantioselective lipase with broad substrate scope for hydrolysis of alpha-substituted esters

A variant of Candida antarctica lipase A (CalA) was developed for the hydrolysis of alpha-substituted p-nitrophenyl esters by directed evolution. The E values of this variant for 7 different esters was 45-276, which is a large improvement compared to 2-20 for the wild type. The broad substrate scope of this enzyme variant is of synthetic use, and hydrolysis of the tested substrates proceeded with an enantiomeric excess between 95-99%. A 30-fold increase in activity was also observed for most substrates. The developed enzyme variant shows (R)-selectivity, which is reversed compared to the wild type that is (S)-selective for most substrates.

A fixed dose combination of ibuprofen and famotidine

The NSAID class of medications is frequently used for mild to moderate pain. While overall safe, NSAIDs have several important adverse effects including esophageal, gastric and duodenal ulceration which limit their use. This has led to the development of NSAIDs with either less gastrointestinal side effects or concurrent use of medications to prevent NSAID gastrointestinal side effects. While several classes of medications exist for the prevention of gastrointestinal side effects, few combination treatments are available in a single pill. Towards this end, a combination pill of ibuprofen and famotidine (HZT-501, Horizon Therapeutics, Skokie, IL. USA) has been developed.

Stereoselective flunoxaprofen-S-acyl-glutathione thioester formation mediated by acyl-CoA formation in rat hepatocytes

Flunoxaprofen (FLX) is a chiral nonsteroidal anti-inflammatory drug that was withdrawn from clinical use because of concerns of potential hepatotoxicity. FLX undergoes highly stereoselective chiral inversion mediated through the FLX-S-acyl-CoA thioester (FLX-CoA) in favor of the (R)-(-)-isomer. Acyl-CoA thioester derivatives of acidic drugs are chemically reactive species that are known to transacylate protein nucleophiles and glutathione (GSH). In this study, we investigated the relationship between the stereoselective metabolism of (R)-(-)- and (S)-(+)-FLX to FLX-CoA and the subsequent transacylation of GSH forming FLX-S-acyl-glutathione (FLX-SG) in incubations with rat hepatocytes in suspension. Thus, when hepatocytes (2 million cells/ml) were treated with (R)-(-)- or (S)-(+)-FLX (100 microM), both FLX-CoA and FLX-SG were detected by sensitive liquid chromatography-tandem mass spectrometry techniques. However, these derivatives were observed primarily from (R)-(-)-FLX incubation extracts, for which the formation rates of FLX-CoA and FLX-SG were rapid, reaching maximum concentrations of 42 and 2.8 nM, respectively, after 6 min of incubation. Incubations with (S)-(+)-FLX over 60 min displayed 8.1 and 2.7% as much FLX-CoA and FLX-SG area under the concentration versus time curves, respectively, compared with corresponding incubations with (R)-(-)-FLX. Coincubation of lauric acid (1000 microM) with (R)-(-)-FLX (10 microM) led to the complete inhibition of FLX-CoA formation and a 98% inhibition of FLX-SG formation. Reaction of authentic (R,S)-FLX-CoA (2 microM) with GSH (10 mM) in buffer (pH 7.4, 37 degrees C) showed the quantitative formation of FLX-SG after 3 h of incubation. Together, these results demonstrate the stereoselective transacylation of GSH in hepatocyte incubations containing (R)-(-)-FLX, which is consistent with bioactivation by stereoselective (R)-FLX-CoA formation.

Cytochrome P450 2C8 pharmacogenetics: a review of clinical studies

Cytochrome P450 (CYP) 2C8 is responsible for the oxidative metabolism of many clinically available drugs from a diverse number of drug classes (e.g., thiazolidinediones, meglitinides, NSAIDs, antimalarials and chemotherapeutic taxanes). The CYP2C8 enzyme is encoded by the CYP2C8 gene, and several common nonsynonymous polymorphisms (e.g., CYP2C8*2 and CYP2C8*3) exist in this gene. The CYP2C8*2 and *3 alleles have been associated in vitro with decreased metabolism of paclitaxel and arachidonic acid. Recently, the influence of CYP2C8 polymorphisms on substrate disposition in humans has been investigated in a number of clinical pharmacogenetic studies. Contrary to in vitro data, clinical data suggest that the CYP2C8*3 allele is associated with increased metabolism of the CYP2C8 substrates, rosiglitazone, pioglitazone and repaglinide. However, the CYP2C8*3 allele has not been associated with paclitaxel pharmacokinetics in most clinical studies. Furthermore, clinical data regarding the impact of the CYP2C8*3 allele on the disposition of NSAIDs are conflicting and no definitive conclusions can be made at this time. The purpose of this review is to highlight these clinical studies that have investigated the association between CYP2C8 polymorphisms and CYP2C8 substrate pharmacokinetics and/or pharmacodynamics in humans. In this review, CYP2C8 clinical pharmacogenetic data are provided by drug class, followed by a discussion of the future of CYP2C8 clinical pharmacogenetic research.

Effect of chirality on PVP/drug interaction within binary physical mixtures of ibuprofen, ketoprofen, and naproxen: a DSC study

We report on the thermal behavior of freshly prepared binary drug/polymer physical mixtures that contained ibuprofen, ketoprofen, or naproxen as a drug, and polyvinylpyrrolidone (PVP), hydroxyethylcellulose (HEC), or methylcellulose (MC) as excipient. At 6-10 degrees C/min heating rates the DSC detected a sharp, single endotherm that corresponds to the melting of drug. On heating physical mixtures of PVP and racemic ibuprofen or ketoprofen at lower heating rates, another endotherm was registered in front of the original one. To observe the additional endotherm, specific minimal values of the heating rate and of PVP weight fraction were needed; for ibuprofen and ketoprofen they were 1.5 and 2.0 degrees C/min, and 5 and 15% (w/w), respectively. At greater PVP weight fractions the top temperatures, T(mp), of both peaks were reduced almost linearly indicating strong solid-state interfacial reaction between the drug particles and PVP matrix. The additional endotherm was abolished at greater heating rates (2 degrees C/min for ibuprofen, 3 degrees C/min for ketoprofen), by replacing the racemate with respective S+-enantiomer and by replacing PVP with HEC and MC. Hence, the possible inclusion of enantioselective component within the PVP/drug interaction, responsible for the amorphization of physical mixture over storage, is assumed.

The effects and safety of dexibuprofen compared with ibuprofen in febrile children caused by upper respiratory tract infection

AIM

To evaluate the antipyretic efficacy and tolerability of dexibuprofen compared with ibuprofen in children with fever caused by upper respiratory tract infection (URTI).

METHODS

The study population consisted of children aged 6 months to 14 years. At the time of visit to the hospital, the children had fever; the cause of fever was determined to be URTI by a paediatrician based on history taking and physical examination. The study was a multicentre, randomized, double-blind, controlled parallel group, comparative, Phase 3 clinical trial, conducted at three hospitals. By using a computer-based random assignment program, the subjects were allocated to the following three groups: 5 mg kg(-1) dexibuprofen group, 7 mg kg(-1) dexibuprofen group, and 10 mg kg(-1) ibuprofen group.

RESULTS

In the clinical trial of the antipyretic action of dexibuprofen in patients with fever caused by URTI, there was no statistically significant difference in maximal decrease of temperature and mean time to become apyrexial among the 5 mg kg(-1) dexibuprofen, 7 mg kg(-1) dexibuprofen and 10 mg kg(-1) ibuprofen groups (P > 0.05). There also was no significant difference in adverse drug reaction (P > 0.05).

CONCLUSIONS

Dexibuprofen is as effective and tolerable as ibuprofen. A dose of 5 mg kg(-1) and 7 mg kg(-1) dexibuprofen in place of 10 mg kg(-1) ibuprofen would be sufficient to control fever caused by URTI in children.

Stereoselective interaction between the CYP2C8 inhibitor gemfibrozil and racemic ibuprofen

OBJECTIVE

Ibuprofen, a nonsteroidal anti-inflammatory agent, is metabolised in vitro by cytochrome P450 (CYP) 2C8 and 2C9. We studied the possible effect of gemfibrozil, an in vivo inhibitor of CYP2C8, on the pharmacokinetics of ibuprofen in healthy volunteers.

METHODS

In a randomised two-phase crossover study, 10 healthy volunteers took 600 mg gemfibrozil or placebo orally twice daily for 3 days. On day 3, each subject ingested 400 mg of racemic ibuprofen. Plasma concentrations of ibuprofen enantiomers and gemfibrozil were measured.

RESULTS

Gemfibrozil raised the mean total area under the plasma concentration-time curve (AUC(0-infinity)) of R-ibuprofen by 34% (range -10 to 67%; P < 0.001). The elimination half-lives (t (1/2)) of R- and S-ibuprofen were increased by 54 and 34% (range 11-162% and 16-85%; P < 0.001) respectively. The other pharmacokinetic variables of R- and S-ibuprofen were not changed significantly. The AUC(0-infinity) ratio of R-ibuprofen to S-ibuprofen was increased by gemfibrozil (P < 0.001).

CONCLUSIONS

Gemfibrozil moderately increases the AUC(0-infinity) of R-ibuprofen and prolongs its t (1/2), indicating that R-ibuprofen is partially metabolised by CYP2C8. The interconversion of R- to S-ibuprofen can explain the small effect of gemfibrozil on the t (1/2) of S-ibuprofen. The gemfibrozil-ibuprofen interaction is of limited clinical significance.

Binding and photochemistry of enantiomeric 2-(3-benzoylphenyl)propionic acid (ketoprofen) in the human serum albumin environment

Global analysis of circular dichroism multiwavelength data and time resolved fluorescence was applied to investigate the interaction of R(-)- and S(+)-ketoprofen (KP) with human serum albumin (HSA) in buffer solution at neutral pH. The most stable drug:protein adducts of 1 : 1 and 2 : 1 stoichiometry were characterized as regards the stability constants and the absolute circular dichroism spectra. The spectra of the diastereomeric 1 : 1 conjugates are negative with minima at ca. 350 nm for R(-)-KP and 330 nm for S(+)-KP, those of the 2 : 1 complexes are both negative with minimum at 340 nm and quite similar in shape to each other, thereby showing that the protein loses chiral recognition capability upon multiple binding. HSA intrinsic time resolved fluorescence data obtained exciting at 295 nm point to Trp 214 being located in the secondary binding site for both KP enantiomers. The photodegradation of the S(+)- and R(-)-KP:HSA complexes was studied by steady state photolysis using lambda(irr) > 320 nm. No decrease of the photodegradation quantum yields was observed in 1 : 1 complexes. An induction time for the photodegradation course in 2 : 1 complexes was observed. Transient absorption spectroscopy at lambda(exc) = 355 nm showed that triplet KP species were formed with stereo-differentiated lifetimes and high quantum yields (0.7-0.9). Secondary transients were consistent with the occurrence of photodecarboxylation and/or photoreduction within the protein matrix.

Effects of the antifungals voriconazole and fluconazole on the pharmacokinetics of s-(+)- and R-(-)-Ibuprofen

Our objective was to study the effects of the antifungals voriconazole and fluconazole on the pharmacokinetics of S-(+)- and R-(-)-ibuprofen. Twelve healthy male volunteers took a single oral dose of 400 mg racemic ibuprofen in a randomized order either alone, after ingestion of voriconazole at 400 mg twice daily on the first day and 200 mg twice daily on the second day, or after ingestion of fluconazole at 400 mg on the first day and 200 mg on the second day. Ibuprofen was ingested 1 h after administration of the last dose of voriconazole or fluconazole. Plasma concentrations of S-(+)- and R-(-)-ibuprofen were measured for up to 24 h. In the voriconazole phase, the mean area under the plasma concentration-time curve (AUC) of S-(+)-ibuprofen was 205% (P < 0.001) of the respective control value and the mean peak plasma concentration (C(max)) was 122% (P < 0.01) of the respective control value. The mean elimination half-life (t(1/2)) was prolonged from 2.4 to 3.2 h (P < 0.01) by voriconazole. In the fluconazole phase, the mean AUC of S-(+)-ibuprofen was 183% of the control value (P < 0.001) and its mean C(max) was 116% of the control value (P < 0.05). The mean t(1/2) of S-(+)-ibuprofen was prolonged from 2.4 to 3.1 h (P < 0.05) by fluconazole. The geometric mean S-(+)-ibuprofen AUC ratios in the voriconazole and fluconazole phases were 2.01 (90% confidence interval [CI], 1.80 to 2.22) and 1.82 (90% CI, 1.72 to 1.91), respectively, i.e., above the bioequivalence acceptance upper limit of 1.25. Voriconazole and fluconazole had only weak effects on the pharmacokinetics of R-(-)-ibuprofen. In conclusion, voriconazole and fluconazole increased the levels of exposure to S-(+)-ibuprofen 2- and 1.8-fold, respectively. This was likely caused by inhibition of the cytochrome P450 2C9-mediated metabolism of S-(+)-ibuprofen. A reduction of the ibuprofen dosage should be considered when ibuprofen is coadministered with voriconazole or fluconazole, especially when the initial ibuprofen dose is high.

Optimization of gas chromatographic method for the enantioseparation of arylpropionic non-steroidal anti-inflammatory drug methyl esters

The gas chromatography (GC) method for enantioseparation of well-known non-steroidal anti-inflammatory drugs ibuprofen, fenoprofen and ketoprofen methyl esters mixture was developed. Best enantioseparation was performed on capillary column with heptakis-(2,3-di-O-methyl-6-O-t-butyldimethyl-silyl)-beta-cyclodextrin stationary phase and hydrogen used as a carrier gas. Initial temperature, program rate and carrier pressure were optimized to obtain best resolution between enantiomers.

The effect of a dexibuprofen mouth rinse on experimental gingivitis in humans

OBJECTIVES

The pharmacodynamic properties of ibuprofen are related nearly exclusively to the S(+)enantiomer (dexibuprofen). This study investigated the effect of a 1.5% dexibuprofen mouth rinse in an experimentally induced gingivitis.

MATERIALS AND METHODS

The trial was a randomized, double-blinded, placebo-controlled, two-period and two-sequence parallel group cross-over study in 24 healthy volunteers aged 21-30 years (16 males, eight females). Customized guards were worn during tooth brushing to prevent any plaque removal from the experimental area (first and second pre-molars and molars in one upper quadrant). After 22 days of plaque accumulation, the mouth rinses (1.5% dexibuprofen and placebo) were administered under supervision three times daily (rinsing for 1 min. with 15 ml) for 8 days. The wash-out time between the two study periods was 14 days. Parameters evaluated at days 0, 7, 14, 22, and 30 were the Löe & Silness gingival index (GI) and the Quigley & Hein plaque index (QHI). Data were tested for treatment, period, and carry-over effects (parametric cross-over analysis).

RESULTS

There was no statistically significant difference (p=0.240) in GI between placebo and dexibuprofen. However, the decrease in QHI was significantly greater (p=0.019) with dexibuprofen as compared with the placebo.

CONCLUSION

In the present study, a 1.5% dexibuprofen mouth rinse had no effect on gingivitis whereas an anti-plaque effect was demonstrated.

The pharmacokinetics of vedaprofen and its enantiomers in dogs after single and multiple dosing

Vedaprofen is a chiral nonsteroidal anti-inflammatory drug that has been developed as a gel formulation for oral administration to dogs and horses. The pharmacokinetics of vedaprofen and its enantiomers were studied in beagle dogs after single (intravenous solution and oral gel) and multiple (oral gel) dosing at a dosage of 0.5 mg/kg body weight. Plasma concentrations of vedaprofen and its enantiomers were analysed by HPLC. The plasma protein binding of vedaprofen was studied by ultrafiltration. The absorption of vedaprofen was rapid (tmax 0.63 +/- 0.14 h) and almost complete after oral administration (bioavailability 86 +/- 7%). The terminal half-lives after intravenous and oral administration, 16.8 +/- 2.2 and 12.7 +/- 1.7 h respectively, were of the same order of magnitude. Enantioselective analysis showed that the R(-) enantiomer predominated in plasma. The change in the plasma time course of the plasma R(-)/S(+) enantiomer concentration ratio over time was similar after single intravenous and oral dosing, with R(-)/S(+) ratios in the AUC of 1.7 +/- 0.5 and 1.9 +/- 0.2 respectively. Plasma protein binding of vedaprofen and its enantiomers was high (> 99.5%). Vedaprofen is absorbed rapidly from the gastrointestinal tract, has a high bioavailability and does not accumulate in plasma in dogs following repeated oral administration.

Pharmacodynamics and pharmacokinetics of nonsteroidal anti-inflammatory drugs in species of veterinary interest

This review summarises selected aspects of the pharmacokinetics (PK) and pharmacodynamics (PD) of nonsteroidal anti-inflammatory drugs (NSAIDs). It is not intended to be comprehensive, in that it covers neither minor species nor several important aspects of NSAID PD. The limited objective of the review is to summarise those aspects of NSAID PK and PD, which are important to an understanding of PK-PD integration and PK-PD modelling (the subject of the next review in this issue). The general features of NSAID PK are: usually good bioavailability from oral, intramuscular and subcutaneous administration routes (but with delayed absorption in horses and ruminants after oral dosing), a high degree of binding to plasma protein, low volumes of distribution, limited excretion of administered dose as parent drug in urine, marked inter-species differences in clearance and elimination half-life and ready penetration into and slow clearance from acute inflammatory exudate. The therapeutic effects of NSAIDs are exerted both locally (at peripheral inflammatory sites) and centrally. There is widespread acceptance that the principal mechanism of action (both PD and toxicodynamics) of NSAIDs at the molecular level comprises inhibition of cyclooxygenase (COX), an enzyme in the arachidonic acid cascade, which generates inflammatory mediators of the prostaglandin group. However, NSAIDs possess also many other actions at the molecular level. Two isoforms of COX have been identified. Inhibition of COX-1 is likely to account for most of the side-effects of NSAIDs (gastrointestinal irritation, renotoxicity and inhibition of blood clotting) but a minor contribution also to some of the therapeutic effects (analgesic and anti-inflammatory actions) cannot be excluded. Inhibition of COX-2 accounts for most and possibly all of the therapeutic effects of NSAIDs. Consequently, there has been an intensive search to identify and develop drugs with selectivity for inhibition of COX-2. Whole blood in vitro assays are used to investigate quantitatively the three key PD parameters (efficacy, potency and sensitivity) for NSAID inhibition of COX isoforms, providing data on COX-1:COX-2 inhibition ratios. Limited published data point to species differences in NSAID-induced COX inhibition, for both potency and potency ratios. Members of the 2-arylpropionate sub-groups of NSAIDs exist in two enantiomeric forms [R-(-) and S-(+)] and are licensed as racemic mixtures. For these drugs there are marked enantiomeric differences in PK and PD properties of individual drugs in a given species, as well as important species differences in both PK and PD properties.

The efficacy of pain control following nonsurgical root canal treatment using ibuprofen or a combination of ibuprofen and acetaminophen in a randomized, double-blind, placebo-controlled study

AIM

To compare ibuprofen, to an ibuprofen/acetaminophen combination in managing postoperative pain following root canal treatment. It is hypothesized that the drug combination will provide more postoperative pain relief than the placebo or ibuprofen alone.

METHODOLOGY

Patients presenting at the Texas A&M Baylor College of Dentistry's graduate endodontic clinic, experiencing moderate to severe pain, were considered potential candidates. Fifty-seven patients were included based on established criteria. Following administration of local anaesthesia, a pulpectomy was performed. The patients were administered a single dose of either: (i) placebo; (ii) 600 mg ibuprofen; or (iii) 600 mg ibuprofen and 1000 mg of acetaminophen. Patients recorded pain intensity following treatment on a visual analogue scale and a baseline four-point category pain scale as well as pain relief every hour for the first 4 h then every 2 h thereafter for a total of 8 h. A general linear model (GLM) analysis was used to analyse the outcome.

RESULTS

Based upon the GLM analysis, there was a significant difference between the ibuprofen and the combination drug group, and between placebo and combination drug groups. There was no significant difference between the placebo and the ibuprofen.

CONCLUSION

The results demonstrate that the combination of ibuprofen with acetaminophen may be more effective than ibuprofen alone for the management of postoperative endodontic pain.

Dexibuprofen: pharmacology, therapeutic uses and safety

Dexibuprofen is the single pharmacologically effective enantiomer of rac-ibuprofen. Racibuprofen and dexibuprofen differ in their physico-chemical properties, in terms of their pharmacological properties and their metabolic profiles. Several clinical trials and post-marketing surveillance studies were performed to broaden the findings on dexibuprofen. In the last 5 years 4836 patients have been exposed to dexibuprofen in clinical trials and PMS trials. Only in 3.7% of patients adverse drug reactions have been reported and 3 serious adverse drug reactions (0.06%) were observed. In the dose ratio of 1 : 0.5 (rac-ibuprofen vs. dexibuprofen) at least equivalent efficacy was proven in acute mild to severe somatic and visceral pain models. Dexibuprofen has proven at least comparable efficacy to diclofenac, naproxen and celecoxib and has shown a favourable tolerability. The results suggest that dexibuprofen processed in a special crystal form is a safe and effective treatment for different pain conditions.

Stereoselective pharmacokinetics and metabolism of flobufen in guinea pigs

Stereoselective aspects of pharmacokinetics and metabolism of a chiral nonsteroidal antiinflammatory drug, flobufen, 4-(2', 4'-difluorobiphenyl-4-yl)-2-methyl-4-oxobutanoic acid, were studied in male guinea pigs after p.o. administration of racemic flobufen (rac-flobufen) at a dose of 10 mg/kg. Blood samples were collected at intervals over 16 h after the administration of rac-flobufen for the quantification of flobufen enantiomers and their respective metabolites in plasma by chiral high-performance liquid chromatography (HPLC). Compartmental pharmacokinetic analysis was used to determine pharmacokinetic parameters of R- and S-flobufen. The plasma concentrations of the S- and R-enantiomers differed significantly during the experimental period. The S/R-enantiomeric ratio in 7plasma reached a maximum value of 10.1 at 240 min postdose. The oral clearance value of R-flobufen was five times higher than S-flobufen. The other pharmacokinetic parameters (K(e), T(1/2), V(SS)/F, MRT) of the enantiomers also differed substantially. All four stereoisomers of the dihydrometabolite of flobufen were detected in plasma with varying concentrations. Metabolite 17203 [4-(2,4-difluorophenyl)-phenylacetic acid] exhibited a relatively longer residence time compared to that noted for the enantiomers of the parent compound. Pharmacokinetics of the flobufen enantiomers were stereoselective in guinea pigs. The metabolism of flobufen was complex. However, metabolite 17203 seemed to be the main metabolite of flobufen that may be responsible for its relatively long-lasting antiphlogistic and immunomodulatory effects.

Influence of age on the enantiomeric disposition of ibuprofen in healthy volunteers

AIMS

To determine the influence of age on the enantioselective disposition of ibuprofen in humans.

METHODS

Healthy young (n = 16; aged 20-36 years) and elderly (n = 16; aged 66-84 years) volunteers were given a 400-mg oral dose of racemic ibuprofen, and blood and urine samples were collected for 24 h post drug administration. Serum concentrations, total and free, and urinary excretion of both enantiomers of ibuprofen together with the urinary excretion of the stereoisomers of the two major metabolites of the drug, both free and conjugated, were determined by high-performance liquid chromatography.

RESULTS

Ageing had little effect on the distribution and metabolism of R-ibuprofen, unbound clearance of the R-enantiomer via inversion being approximately two-fold that via noninversion mechanisms in both age groups. In contrast, the free fraction of S-ibuprofen was significantly greater [33%; young 0.48 +/- 0.10%; elderly 0.64 +/- 0.20%] mean difference -0.16; 95% confidence interval (CI) -0.05, -0.27; P < 0.01; and the unbound clearance of the drug enantiomer was significantly lower (28%; young 15.9 +/- 2.2 l min-1; elderly 11.5 +/- 4.1 l min-1; mean difference 4.4; 95% CI 2.12, 6.68; P < 0.001) in the elderly. The metabolite formation clearances of S-ibuprofen via glucuronidation, and oxidation at the 2- and 3- positions of the isobutyl side chain decreased by 24, 28 and 30%, respectively, in the elderly compared with the young, the differences between the two age groups being significant in each case (P < 0.05).

CONCLUSIONS

Following administration of racemic ibuprofen age-associated stereoselective alterations in drug disposition have been observed, with the elderly having increased free concentrations and lower unbound clearance of the S-enantiomer in comparison with the young. In contrast, the handling of the R-enantiomer is essentially unaltered with age. The results of this study indicate that the elderly have an increased exposure to the active ibuprofen enantiomer and thus some caution may be required when using this drug in this age group.

Pharmacodynamics, chiral pharmacokinetics and PK-PD modelling of ketoprofen in the goat

There have been few studies of the pharmacodynamics of nonsteroidal antiinflammatory drugs (NSAIDs) using PK-PD modelling, yet this approach offers the advantage of defining the whole concentration-effect relationship, as well as its time course and sensitivity. In this study, ketoprofen (KTP) was administered intravenously to goats as the racemate (3.0 mg/kg total dose) and as the single enantiomers, S(+) KTP and R(-) KTP (1.5 mg/kg of each). The pharmacokinetics and pharmacodynamics of KTP were investigated using a tissue cage model of acute inflammation. The pharmacokinetics of both KTP enantiomers was characterized by rapid clearance, short mean residence time (MRT) and low volume of distribution. The penetration of R(-) KTP into inflamed (exudate) and noninflamed (transudate) tissue cage fluids was delayed but area under the curve values were only slightly less than those in plasma, whereas MRT was much longer. The S(+) enantiomer of KTP penetrated less readily into exudate and transudate. Unidirectional inversion of R(-) to S(+) KTP occurred. Both rac-KTP and the separate enantiomers produced marked inhibition of serum thromboxane B2 (TxB2) synthesis (ex vivo) and moderate inhibition of exudate prostaglandin E2 (PGE2) synthesis (in vivo); pharmacodynamic variables for S(+) KTP were Emax (%) = 94 and 100; IC50 (microg/mL) = 0.0033 and 0.0030; N = 0.45 and 0.58, respectively, where Emax is the maximal effect, IC50 the plasma drug concentration producing 50% of Emax and N the slope of log concentration/effect relationship. The IC50 ratio, serum TxB2:exudate PGE2 was 1.10. Neither rac-KTP nor the individual enantiomers suppressed skin temperature rise at, or leucocyte infiltration into, the site of acute inflammation. These data illustrate for KTP shallow concentration-response relationships, probable nonselectivity of KTP for cyclooxygenase (COX)-1 and COX-2 inhibition and lack of measurable effect on components of inflammation.

Ketoprofen in the cat: pharmacodynamics and chiral pharmacokinetics

The non-steroidal anti-inflammatory drug ketoprofen (KTP) was administered as the racemate to cats intravenously (IV) and orally at clinically recommended dose rates of 2 and 1 mg/kg, respectively, to establish its chiral pharmacokinetic and pharmacodynamic properties. After IV dosing, clearance was more than five times greater and elimination half-life and mean residence time were approximately three times shorter for R(-) KTP than for S(+) KTP. Absorption of both S(+) and R(-) enantiomers was rapid after oral dosing and enantioselective pharmacokinetics was demonstrated by the predominance of S(+) KTP, as indicated by plasma AUC of 20.25 (S(+)KTP) and 4.09 (R(-)KTP) microg h/mL after IV and 6.36 (S(+)KTP) and 1.83 (R(-)KTP) microg h/mL after oral dosing. Bioavailability after oral dosing was virtually complete. Reduction in ex vivo serum thromboxane (TX)B(2) concentrations indicated marked inhibition of platelet cyclo-oxygenase (COX)-1 for 24 h after both oral and IV dosing and inhibition was statistically significant for 72 h after IV dosing. Both oral and IV rac-KTP failed to affect wheal volume produced by intradermal injection of the mild irritant carrageenan but wheal skin temperature was significantly inhibited by IV rac-KTP at some recording times. Possible reasons for the disparity between marked COX-1 inhibition and the limited effect on the cardinal signs of inflammation are considered. In a second experiment, the separate enantiomers of KTP were administered IV, each at the dose rate of 1mg/kg. S(+)KTP again predominated in plasma and there was unidirectional chiral inversion of R(-) to S(+)KTP. Administration of both enantiomers again produced marked and prolonged inhibition of platelet COX-1 and, in the case of R(-)KTP, this was probably attributable to S(+)KTP formed by chiral inversion.

Resolution of enantiomers of ketoprofen by HPLC: a review

Today, a heightened awareness of the applicability of enantiomers in medicine and clinical practice has been gene-rated due to the continuous evolvement of the field of chirality. In this context, this article provides a review of separation of ketoprofen, an important drug, in a popular class of non-steroidal anti-inflammatory drugs (i.e. profens). This review highlights various methodologies, logistical considerations for separation and provides an exhaustive list of applications mainly focusing on the pharmacokinetic aspects. Clearly, the application of enantioselective methods for drug racemates paves the way to understand the in vivo behavior of individual enantiomer and hence an opportunity for an alternate and/or better option for treating the disease.

Enantioselective analysis of ibuprofen in human plasma by anionic cyclodextrin-modified electrokinetic chromatography

This paper reports the development of a rapid method for the enantioselective analysis of the nonsteroidal anti-inflammatory drug ibuprofen in human plasma by capillary electrophoresis employing the anionic cyclodextrin-modified electrokinetic chromatography mode. Sample cleanup was carried out by acidification with HCl followed by liquid-liquid extraction with hexane:isopropanol (99:1 v/v). The complete enantioselective analysis was performed within 10 min, using 100 mmol L(-1) phosphoric acid/triethanolamine buffer, pH 2.6, containing 2.0% w/v sulfated beta-cyclodextrin as chiral selector; fenoprofen, another nonsteroidal anti-inflammatory drug, was used as internal standard. The calibration curves were linear over the concentration range of 0.25-125.0 microg mL(-1) for each enantiomer of ibuprofen. The mean recoveries for ibuprofen enantiomers were up to 85%. The enantiomers studied could be quantified at three different concentrations (0.5, 5.0 and 50.0 microg mL(-1)) with a coefficient of variation and relative error not higher than 15%. The quantitation limit was 0.2 microg mL(-1) for (+)-(S)- and (-)-(R)-ibuprofen using 1 mL of human plasma. The plasma endogenous compounds and other drugs did not interfere with the present assay. The analysis of real plasma samples obtained from a healthy volunteer after administration of 600 mg of racemic ibuprofen showed a maximum plasma level of 29.6 and 39.9 microg mL(-1) of (-)-(R)- and (+)-(S)-ibuprofen, respectively, and the area under plasma concentration-time curve AUC(0-infinity) (+)-(S)/AUC(0-infinity) (-)-(R) ratio was 1.87.

Clinical efficacy and pharmacokinetics of carprofen in the treatment of dogs with osteoarthritis

Six medium to large breed dogs with osteoarthritis were treated with 2 mg/kg of racemic carprofen, mixed with their morning feed, daily for 28 days. The treatment significantly (P < 0.01) reduced their mean lameness score, measured on a visual analogue scale, and there was a trend (P = 0.11) for the peak vertical forces exerted on a forceplate to be increased in the most severely affected limb. The plasma concentration-time relationships of the S(+) and R(-) enantiomers were studied for 24 hours after the first dose and after seven days and 28 days. There were no significant differences between the mean pharmacokinetic parameters measured on the three occasions, suggesting that carprofen was not accumulated and that tolerance to the drug did not develop. Although the pharmacokinetic parameters of the S(+) and R(-) enantiomers were generally very similar, there were wide variations both between and within dogs.

Chirality: a blueprint for the future

The chirality that is inherent in the enzyme systems of living organisms results in an abundance of enantiopure organic molecules in the living world. In addition to the optical properties first noticed by Pasteur, stereospecific interactions at recognition sites result in differences in both biological and toxicological effects. This fact underlies the continuing growth in chiral chemistry, rooted as it is in fundamental biochemistry. The pharmaceutical industry has undergone a strategic shift and embraced the wide spectrum of asymmetrical synthetic methods now available. The use of these processes in developmental synthesis and large-scale manufacturing has provided new challenges in drug discovery, motivated by a desire to improve industrial efficacy and decrease the time from the conception of a new drug to the market. The economic impact of the industrial production of chiral drugs is now huge--more than 50% of the 500 top-selling drugs were single-enantiomers in 1997. Sales have continued to increase by more than 20% for the past 6 yr and worldwide annual sales of enantiomeric drugs exceeded US$100 billion for the first time in the year 2000, chiral drugs representing close to one-third of all sales worldwide. While some 'chiral switches' may be of less apparent benefit, or indeed detrimental in some cases, encouragement by the regulatory agencies and the ability to extend the life cycle of a drug coming off patent promotes the trend. However, it may turn out to be the ability to provide chiral templates, and thereby attack the key targets of selectivity and specificity, that will lead to the greatest benefits. Research into new chemical entities that can interact specifically with enzyme families may potentially lead to new therapies for complex disease processes. As Richards has stated, the approach is designed to create a made to measure product, rather than one off the peg.

Biotransformation of flobufen enantiomers in ruminant hepatocytes and subcellular fractions

Flobufen (F), a new antiinflammatory drug, has one chiral and one prochiral center in its structure. Reduction of rac-F, the principal biotransformation pathway, leads to the formation of four diastereoisomers of 4-dihydroflobufen (DHF). F was chosen as a model substrate for interspecies comparison of activity, stereospecificity, and stereoselectivity of biotransformation enzymes in fallow bucks, red deer stags, and roe bucks in vitro. Formation of F metabolites was examined in hepatocyte suspension and in subcellular fractions of liver homogenate. (+)-R-F, (-)-S-F and rac-F were used as substrates. After incubation of substrates, the amounts and ratios of DHF diastereoisomers and F enantiomers were assessed by HPLC, with (R,R)-ULMO and terguride-bonded columns. Considerable interspecies differences in stereoselectivity and stereospecificity of F reductases were found at the cellular and subcellular levels, although these ruminants are closely related. Chiral inversion of F enantiomers to their antipodes was detected in vitro in all ruminants tested, but individual species also differed in the direction and rate of this inversion.

Influence of a polymeric formulation of ketoprofen on its diffusion into cerebrospinal fluid in rats

Poly(D,L)lactide nanocapsules (NCs) have been proposed as an alternative carrier for many drugs. We investigated the influence of this formulation on the pharmacokinetics of ketoprofen in the plasma and cerebrospinal fluid (CSF). Male Wistar rats were given intraperitoneal dose of ketoprofen (5 mg/kg) in a suspension of NCs or in a carboxymethylcellulose (CMC) solution (reference preparation). Blood and CSF samples were collected at different times up to 24 h after dosing. The unbound fraction of ketoprofen in plasma (f(u)) was determined using ultrafiltration. The total (C(T)) and free (C(F)) concentrations of ketoprofen in plasma and the simultaneous CSF concentrations (C(CSF)) were measured by a HPLC method and the areas under the curve (AUC(T), AUC(F), AUC(CSF)) were calculated. AUC(T) of ketoprofen-loaded NCs in plasma was similar to that of the reference solution, while AUC(F) of the former (5.41 mg/l x h) was higher than that produced by the latter (4.03 mg/l x h). Accordingly, the unbound fraction (f(u)) was higher after administration of NCs than that of the solution (2.5 and 1.8%, respectively). Finally, AUC(CSF) were identical for both formulations. These findings suggest that the binding of ketoprofen to plasma proteins is not the major factor that governs its blood-to-CSF exchanges.

Stereochemistry and drug efficacy and development: relevance of chirality to antidepressant and antipsychotic drugs

Many drugs contain a chiral center or a center of unsaturation, or such centers result during metabolism of these drugs. Often such drugs are marketed as a mixture of the resultant enantiomers (racemates) or of geometric isomers, respectively. These enantiomers (molecules that are not superimposible on their mirror image) or geometric isomers may differ markedly from each other with regard to their pharmacodynamic and/or pharmacokinetic properties. This review deals primarily with drugs with chiral centers, and possible complications arising from the use of racemates are discussed. Recent developments in resolution of enantiomers, increased knowledge of the molecular structure of specific drug targets and a heightened awareness of several possible advantages of using single enantiomers rather than racemic mixtures of drugs have led to an increased emphasis on understanding the role of chirality in drug development. This has resulted in increased investigation of individual enantiomers early on in the development of drugs and in 'chiral switching', i.e. the replacement of a racemate of a drug which has already been approved or marketed by a single enantiomer. Although stereochemistry is an important matter to consider in drugs of virtually all classes, this review focuses on the relevance of chirality to antidepressant and antipsychotic drugs. Examples of the effects of chiral centers on the properties of antidepressants (tricyclics, selective serotonin reuptake inhibitors, monoamine oxidase inhibitors, viloxazine, bupropion, mianserin, venlafaxine, mirtazapine and reboxetine), antipsychotics and/or some of their metabolites are discussed.

Comparative pharmacology of S(+)-ibuprofen and (RS)-ibuprofen

Racemic ibuprofen, which contains equal quantities of R(-)-ibuprofen and S(+)-ibuprofen, has been used as an anti-inflammatory and analgesic agent for over 30 years. Although the S(+)-enantiomer is capable of inhibiting cyclooxygenase (COX) at clinically relevant concentrations, R(-)-ibuprofen is not a COX inhibitor. The two enantiomers of ibuprofen are therefore different in terms of their pharmacological properties and may be regarded as two different 'drugs'. They also differ in terms of their metabolic profiles. For example, R(-)-ibuprofen becomes involved in pathways of lipid metabolism and is incorporated into triglycerides along with endogenous fatty acids. S(+)-Ibuprofen does not appear to become involved in these unusual metabolic reactions, which is why S(+)-ibuprofen is regarded as being metabolically 'cleaner' than racemic ibuprofen. When racemic ibuprofen is given to humans, a substantial fraction of the dose of R(-)-ibuprofen (50%-60%) undergoes 'metabolic inversion' to yield S(+)-ibuprofen. On this basis, it has been argued that to obtain clinical effects that are comparable to those of a given dose of racemic ibuprofen, the dose of S(+)-ibuprofen would need to be about 75% of the dose of the racemate. However, this 'pharmacokinetic' rationale does not take into account the fact that inversion is not instantaneous, that there is variability in the extent of inversion between individuals, and that the kinetics of inversion may differ depending on the dosing situations. For example, the extent of inversion appears to be reduced when the racemate is given to patients experiencing acute pain. Recent studies have demonstrated that the clinical benefits of racemic ibuprofen can be derived from the administration of the single S(+)-enantiomer at a dose that is half that of the racemate. For example, 200 mg of S(+)-ibuprofen has been found to be superior or at least equivalent to 400 mg of the racemate in the relief of dental pain. Possible explanations for this higher than expected efficacy of S(+)-ibuprofen are considered.

Pharmacodynamics and pharmacokinetics of ketoprofen enantiomers in sheep

OBJECTIVE

To establish pharmacokinetic and pharmacodynamic properties of a racemic mixture and individual R(-) and S(+) enantiomeric forms of ketoprofen (KTP) in sheep and determine pharmacodynamic variables of KTP by pharmacokinetic-pharmacodynamic modeling.

ANIMALS

8 female Dorset crossbred sheep.

PROCEDURE

A tissue cage model of inflammation was used. Carrageenan was administered into tissue cages. Time course of cyclooxygenase (COX)-2 inhibition was determined in vivo by measurement of exudate prostaglandin E2 (PGE2) concentrations. Time course of COX-1 inhibition was determined ex vivo by measurement of serum thromboxane B2 (TXB2) concentrations. In addition, plasma concentration-time course and penetration of KTP enantiomers into inflammatory exudate and transudate (noninflamed tissue cage fluid) were investigated. Four treatments were compared: placebo, racemic mixture (rac-KTP [3 mg/kg of body weight, IV]), S(+) KTP (1.5 mg/kg, IV),and R(-) KTP (1.5 mg/kg, IV).

RESULTS

Both KTP enantiomers had elimination half-life and mean residence time measurements that were short and volume of the central compartment and steady state volume of distribution that were low. Clearance was rapid, particularly for R(-) KTP Elimination of both enantiomers from exudate was > 10 times slower than from plasma. Both rac-KTP and the individual enantiomers significantly inhibited serum TXB2 concentrations for 12 hours. Rac-KTP and S(+) KTP, but not R(-) KTP, also significantly inhibited PGE2 synthesis in exudate for 12 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

Inhibition of serum TXB2 concentration and exudate PGE2 synthesis for similar time courses after S(+) KTP administration indicates that it is a nonselective inhibitor of COX in sheep.

Chiral bioequivalence: effect of absorption rate on racemic etodolac

BACKGROUND

For many racemic drugs, bioequivalence assessment based on isomer-nonspecific assays is appropriate because enantiomeric area under the concentration-time curve (AUC) exposure ratios are close to unity. Use of nonspecific methods in cases in which the ratio is substantially greater or less than 1, however, may obscure real therapeutic differences among formulations, especially if the enantiomers exhibit differing pharmacological potencies.

OBJECTIVE

To examine the influence of absorption rate on etodolac bioequivalence as measured by total [(R,S)-] and (S)-etodolac.

DESIGN

Single dose, 3-period, crossover, pharmacokinetic study in 24 healthy volunteers in which the administration rate of etodolac was varied.

METHODS

Participants received etodolac 400mg in solution, given as a single dose over 1 minute or as divided doses over 30 and 90 minutes. Unresolved and enantiomer concentrations of etodolac were measured by a validated HPLC assay. The enantiomer ratio was similarly measured by HPLC.

RESULTS

Bioequivalence parameters derived for both unresolved and (S)etodolac indicate that peak plasma drug concentration (Cmax) was not bioequivalent. By delaying absorption, bioequivalence was lost.

CONCLUSIONS

Collectively, these data demonstrate that bioequivalence between 2 products of etodolac based on enantiomerically nonspecific criteria alone may not generalise to the pharmacologically relevant (S)-enantiomer. This suggests that enantiospecific assays are necessary for bioequivalence assessments.

Chiral inversion of R(-) fenoprofen and ketoprofen enantiomers in cats

The chiral inversion process is a characteristic metabolic pathway for different aryl-2-propionic acids or profens. Important variations have been observed between these individual compounds as well as between animal species. In this study, R(-) fenoprofen [R(-)FPF] and R(-) ketoprofen [R(-) KTF] were used to investigate their comparative stereoconversion in cats. After intravenous (i.v.) administration of R(-) FPF, the percentage of chiral inversion was 93.20+/-13.70%. A highly significant correlation (r: 0.978) was observed between the clearance of R(-) FPF and the chiral inversion process. After i.v. administration of R(-) KTF, the percentage of inversion was only 36.73+/-2.8%. No correlation between the clearance of R(-) KTF and this process was observed. R(-) FPF was metabolized by the pathways of thioesterification - chiral inversion processes. For R(-) KTF, the competitive metabolic pathways, glucuronidation and hydroxylation may be involved. However, these metabolic steps are saturable or less functional in cats. Moreover, the thioesterification of R(-) KTF in in vitro studies has been shown to be important in carnivores. The lack of correlation between clearance and chiral inversion process of R(-) KTF may be finally explained by deviation of thioesterification to other metabolic pathways of lipids and/or aminoacid conjugation, particulary glicine derivatives.

Synthesis, chromatographic resolution and chiroptical properties of carboxyibuprofen stereoisomers: major metabolites of ibuprofen in man

The chromatographic resolution of the four stereoisomers of carboxy-ibuprofen, a major metabolite of ibuprofen in man, was achieved using a Chiralpak AD chiral stationary phase (CSP) (J.T. Baker, Milton, Keynes, UK). The elution order of the stereoisomers was determined to be 2'S,2R;2'R,2R;2'R,2S;2'S,2S by a combination of stereoselective synthesis of diastereoisomeric mixtures and analysis of the two diastereoisomers isolated from human urine following the administration of (S)-ibuprofen. The individual stereoisomers were isolated by semipreparative chiral phase chromatography and characterized by circular dichroism spectroscopy.

Enantiospecific analysis by capillary electrophoresis: applications in drug metabolism and pharmacokinetics

Enantiospecific analysis has an important role in drug metabolism and pharmacokinetic investigations and its now no longer acceptable to determine total drug, or metabolite, concentrations following the administration of a racemate. Inspite of the fact that capillary electrophoresis (CE) has become an essential technique in pharmaceutical and enantiospecific analysis, the chromatographic methodologies remain the most commonly used approach for the determination of the enantiomeric composition of drugs in biological fluids. The application of CE to bioanalysis has been slow, which is in part associated with the complexity of biological matrices together with the relatively poor concentration limits of detection achievable. However, as a result of its versatility, high separation efficiency, minimal sample requirements, speed of analysis and low consumable expense CE is likely to play an increasingly significant role in the area. This review present an overview of enantiospecific CE in bioanalysis in which the approaches to enantiomeric resolution and the problems associated with biological matrices are briefly discussed. The application of enantiospecific CE to samples of biological origin is illustrated using examples where the methodology has either solved an analytical problem, or provided a useful alternative to the currently available chromatographic methods. Such improvements in methodology are associated with either the high separation efficiency and/or microanalytical capabilities of the technique. Enantiospecific CE will not replace the chromatographic methodologies but does provide the bioanalyst with a useful addition to his armamentarium.

Choosing the right nonsteroidal anti-inflammatory drug for the right patient: a pharmacokinetic approach

Effective use of the growing number of nonsteroidal anti-inflammatory drugs (NSAIDs), a group that has recently been augmented by the introduction of the selective cyclo-oxygenase-2 inhibitors, requires adequate knowledge of their pharmacokinetics. After oral administration, the absorption of NSAIDs is generally rapid and complete. NSAIDs are highly bound to plasma proteins, specifically to albumin (>90%). The volume of distribution of NSAIDs is low, ranging from 0.1 to 0.3 L/kg, suggesting minimal tissue binding. NSAID binding in plasma can be saturated when the concentration of the NSAID exceeds that of albumin. Most NSAIDs are metabolised by the liver, with subsequent excretion into urine or bile. Enterohepatic recirculation occurs when a significant amount of an NSAID or its conjugated metabolites are excreted into the bile and then reabsorbed in the distal intestine. NSAID elimination is not dependent on hepatic blood flow. Hepatic NSAID elimination is dependent on the free fraction of NSAID within the plasma and the intrinsic enzyme activities of the liver. Renal elimination is not an important elimination pathway for NSAIDs, except for azapropazone. The plasma half-life of NSAIDs ranges from 0.25 to >70 hours, indicating wide differences in clearance rates. Hepatic or renal disease can alter NSAID protein binding and metabolism. Some NSAIDs with elimination predominantly via acylglucuronidation can have significantly altered disposition. Pharmacokinetics are also influenced by chronobiology, and many NSAIDs exhibit stereoselectivity. There appear to be relationships between NSAID concentration and effects. At therapeutically equivalent doses, NSAIDs appear to be equally efficacious. The major differences between NSAIDs are their therapeutic half-lives and safety profiles. NSAIDs undergo drug interactions through protein binding displacement and competition for active renal tubular secretion with other organic acids. When choosing the right NSAID for the right patient, individual patient-specific and NSAID-specific pharmacokinetic principles should be considered.

Enantiospecific pharmacokinetics and pharmacodynamics of ketoprofen in sheep

Pharmacokinetic and pharmacodynamic parameters were established for the enantiomers of the 2-arylpropionic acid (APA) nonsteroidal anti-inflammatory drug (NSAID), ketoprofen (KTP). Each enantiomer was administered separately (1.5 mg/kg) and in a racemic mixture (3 mg/kg) intravenously (i.v.) to a group of eight sheep in a four-way, four-period cross-over study using a tissue cage model of inflammation. Plasma disposition of each KTP enantiomer was similar following separate administration of the pure compounds compared to administration of the racemic mixture. S(+)KTP volume of distribution (Vd(area)) was higher and clearance (ClB) faster than those of R(-)KTP. S(+) and R(-)KTP achieved relatively low concentrations in exudate and transudate. Unidirectional limited chiral inversion of R(-) to S(+)KTP was demonstrated. After R(-)KTP administration S(+)KTP was detected in plasma, but not in either exudate or transudate. Pharmacokinetic/pharmacodynamic (PK/PD) modelling of the data could not be undertaken following R(-)KTP administration because of chiral inversion to S(+)KTP, but the pharmacodynamic parameters, calculated maximum effect (Emax), concentration producing 50% effect (EC50), Hill's coefficient (N), rate constant of elimination of drug effect from the compartment (KeO) and mean equilibration half-life (t1/2KeO) were determined for S(+)KTP after administration of the racemic mixture as well as the pure compound.

Stereoselective pharmacokinetics of flobufen in rats

Stereoselectivity of the pharmacokinetics of the nonsteroidal anti-inflammatory drug flobufen, 4-(2', 4'-difluorobiphenyl-4-yl)-2-methyl-4-oxobutanoic acid, was studied in male Wistar rats after intravenous administration. Pharmacokinetic parameters and chiral inversion of flobufen enantiomers were studied after a bolus injection of the racemate and individual enantiomers (5 mg/kg). Determinations of the enantiomers in rat plasma were performed using chiral HPLC (terguride column). After i.v. administration of flobufen racemate, plasma levels of R-enantiomer decreased more rapidly. The S-/R-enantiomer ratio of AUCs after rac-flobufen was 13.3. The total plasma clearance value of S-flobufen was more than 10-fold lower than R-flobufen. The other pharmacokinetic parameters of the enantiomers were also significantly different. While only traces of R-enantiomer (less than 1%) were detected in rat plasma after S-flobufen administration, considerable conversion to the S-enantiomer was found after injection of R-flobufen (R-enantiomer AUC/S-enantiomer AUC = 0.52). The results indicate substantial stereoselectivity in the disposition of flobufen enantiomers in the rat, which is, at least in part, attributed to chiral bioconversion.

Chromatographic resolution, chiroptical characterization and preliminary pharmacological evaluation of the enantiomers of butibufen: a comparison with ibuprofen

Enantiomeric resolution of butibufen has been achieved on a cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase with hexane-isopropanol-trifluoroacetic acid, 100:1.2:0.02 (v/v/v) as mobile phase at a flow rate of 1.0 mL min(-1). Semi-preparative isolation of the enantiomers then chiroptical characterization indicated that the order of elution was (-)-R- before (+)-S-butibufen. When tested for their effects on the cyclooxygenase and 5-lipoxygenase pathways of eicosanoid metabolism in calcium ionophore-activated rat peritoneal leukocytes it was found that (+)-S-butibufen inhibited generation of thromboxane B2 (TXB2) and prostaglandin E2 (PGE2) (cyclooxygenase pathway), with an IC50 of 1.5 microM (approx.), whereas the (-)-R enantiomer was essentially inactive. Neither enantiomer inhibited the 5-lipoxygenase pathway. In this regard, (+)-S-butibufen was approximately five times less potent as a cyclooxygenase inhibitor than (+)-S-ibuprofen. These results show the enantiomeric specificity and pathway selectivity of this novel non-steroidal anti-inflammatory drug.

In vitro stimulation of equine articular cartilage proteoglycan synthesis by hyaluronan and carprofen

The effects of hyaluronan and carprofen (both racemic mixture and separate R and S enantiomers) on proteoglycan (PG) synthesis by equine cultured chondrocytes and cartilage explants were examined. Hyaluronan stimulated PG synthesis in both cell and explant cultures. The concentration-response curve of the latter was bell-shaped. Racemic carprofen and R and S enantiomers also stimulated PG synthesis, although concentration-response relationships varied for each preparation and high concentrations inhibited synthesis. It was concluded that (a) hyaluronan exerts a stimulatory effect on PG synthesis at low concentrations and (b) stimulatory effects of carprofen on PG synthesis are, to some degree, enantioselective with the carprofen S-enantiomer exerting the greatest effect. Hyaluronan and carprofen are used clinically despite incompletely understood mechanisms of action. These results suggest (a) hyaluronan and carprofen might exert an anti-arthritic action through stimulation of PG synthesis and (b) there is possible justification for therapeutic administration of enantiomeric rather than racemic carprofen.

Inhibition of cytokine production and adhesion molecule expression by ibuprofen is without effect on transendothelial migration of monocytes

The present study focusses on the effects of ibuprofen and its enantiomers on cytokine production by peripheral blood monocytes and endothelial cells as well as on the potential modulation of ADM-expression by human umbilical vein endothelial cells and the concomitant effects on monocyte transendothelial migration as measured by a cell migration assay system. This consists of an endothelial cell monolayer on a solid collagen substrate, i.e. an artificial vessel wall construct. We observed a significant inhibition by 100 microg/ml ibuprofen of VCAM-1 expression by endothelial cells while ELAM-1 and ICAM-1 expression was not influenced. However, we could not see any concomitant inhibitory effects on the spontaneous migration of monocytes after preincubating the endothelial cell monolayer with ibuprofen up to concentrations of 100 microg/ml and activating with suboptimal and optimal concentrations of TNF-alpha. Our monocyte transendothelial migration system reflects very sensitively endothelial cell-activation even by very low TNF-alpha concentrations. (S)- and (R)-ibuprofen were equal in their inhibitory/activating effects on cytokine production, with the exception of stronger IL-8 induction in endothelial cells by (R)-ibuprofen as compared to its chiral analogue.

Chirality and drugs used in psychiatry: nice to know or need to know?

1. Many drugs used to treat psychiatric disorders contain a chiral center or a center of unsaturation and are marketed as a mixture of the resultant enantiomers or geometric isomers, respectively. These enantiomers or geometric isomers may differ markedly with regard to their pharmacodynamic and/or pharmacokinetic properties. 2. Examples of the effects of chiral centers or geometric centers on such properties are given for drugs from the following classes: antidepressants (tricyclics, selective serotonin reuptake inhibitors, monoamine oxidase inhibitors, viloxazine, bupropion, trazodone, mianserin, venlaflaxine); benzodiazepines, zoplicone, and antipsychotics. 3. As described in this review, there are several notable examples of psychiatric drugs currently available where the individual enantiomers or geometric isomers differ considerably with regard to factors such as effects on amine transport systems, interactions with receptors and metabolizing enzymes, and clearance rates from the body. Indeed, relatively recent developments in analytical and preparative resolution of racemic and geometric drug mixtures and increased interest in developing new drugs which interact with specific targets, which have been described in detail at the molecular level, have resulted in increased emphasis on stereochemistry in drug development.

A pharmacodynamic and pharmacokinetic study with vedaprofen in an equine model of acute nonimmune inflammation

The pharmacodynamics and enantioselective pharmacokinetics of vedaprofen were studied in six ponies in a two period cross-over study, in which a mild acute inflammatory reaction was induced by carrageenan soaked sponges implanted subcutaneously in the neck. Vedaprofen, administered intravenously at a dosage of 1 mg/kg, produced significant and prolonged inhibition of ex vivo serum thromboxane B2 (TXB2) synthesis and short-lived inhibition of exudate prostaglandin E2 (PGE2) and TXB2 synthesis. Vedaprofen also partially inhibited oedematous swelling and leucocyte infiltration into exudate. Vedaprofen displayed enantioselective pharmacokinetics, plasma concentrations of the R(-) enantiomer exceeding those of S(+) vedaprofen. The plasma concentration ratio, R:S, increased from 69:31 at 5 min to 96:4 at 3 h and plasma mean AUC values were 7524 and 1639 ng x h/mL, respectively. Volume of distribution was greater for S(+) vedaprofen, whilst elimination half-life (t(1/2beta)) and mean residence time were greater for R(-) vedaprofen. The penetration of vedaprofen into inflammatory exudate was also enantioselective. For R(-) and S(+) vedaprofen maximum concentration (Cmax) values were 2950 and 1534 ng/mL, respectively, and corresponding AUC values were 9755 and 4400 ng x h/mL. Vedaprofen was highly protein bound (greater than 99%) in both plasma and exudate. The significance of these data for the therapeutic use of vedaprofen is discussed.

Passage of S-(+)- and R-(-)-ketoprofen across the human isolated perfused placenta

Ketoprofen is a chiral non-steroidal anti-inflammatory drug (NSAID) available as a racemic (rac) mixture of S-(+)- and R-(-)-isomers. Its inhibitory effect on prostaglandin biosynthesis resides virtually in the S-form. Interestingly, R-ketoprofen does not undergo substantial metabolic inversion in humans. Though contraindicated during the last trimester of pregnancy, NSAIDs, including ketoprofen, are used as tocolytic agents in some cases. The S/R plasma concentration ratio was reported to average 2.3 in premature neonates whose mothers were given rac-ketoprofen and to be close to 1 in the maternal plasma. Thus, we investigated the placental transfer of rac-ketoprofen in vitro using Schneider's perfused human cotyledon model. Glucosed Earle solutions with and without human serum albumin (HSA) were used. Several maternal perfusates were tested with different rac-ketoprofen concentrations together with 20 mg L-1 of antipyrine as a reference substance. Ketoprofen enantiomers were assayed by a specific HPLC method with derivatization procedure. HSA concentrations in maternal perfusate influenced the placental transfer of ketoprofen enantiomers. In the absence of HSA in the maternal perfusate, the S-(+)/R-(-) concentration ratio was close to 1 in the fetal perfusate. By contrast, this ratio averaged 1.44 after addition of HSA 10 g L-1 on the maternal side. Similar results were found for dialysis experiments using an inert Spectrapor 2 membrane suggesting that the S-(+)-free concentration is superior to the R-(-)-free concentration in the presence of HSA. Direct measurements of the free concentrations by centrifugal ultrafiltration confirmed this hypothesis. Accordingly, the data observed in vivo may result, at least in part, from the stereoselective protein binding of ketoprofen.