Bi-directional chiral inversion of ketoprofen in CD-1 mice

Computer-aided analysis for identification of novel analogues of ketoprofen based on molecular docking, ADMET, drug-likeness and DFT studies for the treatment of inflammation

Computer-based drug design is increasingly used in strategies for discovering new molecules for therapeutic purposes. The targeted drug is ketoprofen (KTP), which belongs to the family of non-steroidal anti-inflammatory drugs, which are widely used for the treatment of pain, fever, inflammation and certain types of cancers. In an attempt to rationalize the search for 72 new potential anti-inflammatory compounds on the COX-2 enzyme, we carried out an in silico protocol that successfully combines molecular docking towards COX-2 receptor (5F1A), ADMET pharmacokinetic parameters, drug-likeness rules and molecular electrostatic potential (MEP). It was found that six of the compounds analyzed satisfy with the associated values to physico-chemical properties as key evaluation parameters for the drug-likeness and demonstrate a hydrophobic character which makes their solubility in aqueous media difficult and easy in lipids. All the compounds presented good ADMET profile and they showed an interaction with the amino acids responsible for anti-inflammatory activity of the COX-2 isoenzyme. The calculation of the MEP of the six analogues reveals new preferential sites involving the formation of new bonds. Consequently, this result allowed us to understand the origin of the potential increase in the anti-inflammatory activity of the candidates. Finally, it was obtained that six compounds have a binding mode, binding energy, and stability in the active site of COX-2 like the reference drug ketoprofen, suggesting that these compounds could become a powerful candidate in the inhibition of the COX-2 enzyme.Communicated by Ramaswamy H. Sarma.

Ecotoxicological properties of ketoprofen and the S(+)-enantiomer (dexketoprofen): Bioassays in freshwater model species and biomarkers in fish PLHC-1 cell line

The increased use of nonsteroidal anti-inflammatory drugs (NSAIDs) has resulted in their ubiquitous presence in the environment. The toxicological properties of these 2 widely prescribed NSAIDs, namely racemic ketoprofen and its enantiomer S(+)-ketoprofen (dexketoprofen), were evaluated, firstly, by acute and chronic toxicity tests using 3 representative model organisms (Vibrio fischeri, Pseudokirchneriella subcapitata, and Ceriodaphnia dubia) and, secondly, by evaluating the responses of biotransformation systems and multidrug resistance-associated proteins (MRP1/MRP2) using the Poeciliopsis lucida hepatocellular carcinoma 1 (PLHC-1) fish hepatic cell line. Toxicity data from both acute and chronic dexketoprofen exposure indicated higher sensitivity through inhibition of bioluminescence and algal growth and through increased mortality/immobilization compared to racemic ketoprofen exposure. The growth inhibition test showed that racemic ketoprofen and dexketoprofen exhibited different effect concentration values (240.2 and 65.6 μg/L, respectively). Furthermore, racemic ketoprofen and dexketoprofen did not exert cytotoxic effects in PLHC-1 cells and produced compound-, time-, and concentration-specific differential effects on cytochrome P450 1A (CYP1A) and glutathione S-transferase levels. For CYP1A, the effects of racemic ketoprofen and dexketoprofen differed at the transcriptional and catalytic levels. Exposure to racemic ketoprofen and dexketoprofen modulated MRP1 and MRP2 mRNA levels, and these effects were also dependent on compound, exposure time, and concentration of the individual drug. The present study revealed for the first time the interactions between these NSAIDs and key detoxification systems and different sensitivity to the racemic mixture compared to its enantiomer. Environ Toxicol Chem 2018;37:201-212. © 2017 SETAC.

Impact of chirality on the photoinduced charge transfer in linked systems containing naproxen enantiomers

The model reaction of photoinduced donor-acceptor interaction in linked systems (dyads) has been used to study the comparative reactivity of a well-known anti-inflammatory drug, (S)-naproxen (NPX) and its (R)-isomer. (R)- or (S)-NPX in these dyads is linked to (S)-N-methylpyrrolidine (Pyr) using a linear or cyclic amino acid bridge (AA or CyAA), to give (R)-/(S)-NPX-AA-(S)-Pyr flexible and (R)-/(S)-NPX-CyAA-(S)-Pyr rigid dyads. The donor-acceptor interaction is reminiscent of the binding (partial charge transfer, CT) and electron transfer (ET) processes involved in the extensively studied inhibition of the cyclooxygenase enzymes (COXs) by the NPX enantiomers. Besides that, both optical isomers undergo oxidative metabolism by enzymes from the P450 family, which also includes ET. The scheme proposed for the excitation quenching of the (R)- and (S)-NPX excited state in these dyads is based on the joint analysis of the chemically induced dynamic nuclear polarization (CIDNP) and fluorescence data. The (1)H CIDNP effects in this system appear in the back electron transfer in the biradical-zwitterion (BZ), which is formed via dyad photoirradiation. The rate constants of individual steps in the proposed scheme and the fluorescence quantum yields of the local excited (LE) states and exciplexes show stereoselectivity. It depends on the bridge's length, structure and solvent polarity. The CIDNP effects (experimental and calculated) also demonstrate stereodifferentiation. The exciplex quantum yields and the rates of formation are larger for the dyads containing (R)-NPX, which let us suggest a higher contribution from the CT processes with the (R)-optical isomer.

Preparation and the biopharmaceutical evaluation for the metered dose transdermal spray of dexketoprofen

The objective of the present work was to develop a metered dose transdermal spray (MDTS) formulation for transdermal delivery of dexketoprofen (DE). DE release from a series of formulations was assessed in vitro. Various qualitative and quantitative parameters like spray pattern, pump seal efficiency test, average weight per metered dose, and dose uniformity were evaluated. The optimized formulation with good skin permeation and an appropriate drug concentration and permeation enhancer (PE) content was developed incorporating 7% (w/w, %) DE, 7% (v/v, %) isopropyl myristate (IPM), and 93% (v/v, %) ethanol. In vivo pharmacokinetic study indicated that the optimized formulation showed a more sustainable plasma-concentration profile compared with the Fenli group. The antiinflammatory effect of DE MDTS was evaluated by experiments involving egg-albumin-induced paw edema in rats and xylene-induced ear swelling in mice. Acetic acid-induced abdominal constriction was used to evaluate the anti-nociceptive actions of DE MDTS. Pharmacodynamic studies indicated that the DE MDTS has good anti-inflammatory and anti-nociceptive activities. Besides, skin irritation studies were performed using rat as an animal model. The results obtained show that the MDTS can be a promising and innovative therapeutic system used in transdermal drug delivery for DE.

Analysis of chiral non-steroidal anti-inflammatory drugs flurbiprofen, ketoprofen and etodolac binding with HSA

The protein binding of non-steroidal anti-inflammatory drugs flurbiprofen, ketoprofen and etodolac with human serum albumin (HSA) was investigated using indirect chiral high performance liquid chromatography (HPLC) and ultrafiltration techniques. S-(–)-1-(1-naphthyl)-ethylamine (S-NEA) was utilized as chiral derivatization reagent and pre-column derivatization RP-HPLC method was established for the separation and assay of the three pairs of enantiomer. The method had good linear relationship over the investigated concentration range without interference. The average extraction efficiency was higher than 85% in different systems, and the intra-day and inter-day precisions were less than 15%. In serum albumin, the protein binding of etodolac enantiomers showed significant stereoselectivity that the affinity of S-enantiomer was stronger than R-enantiomer, and the stereoselectivity ratio reached 6.06; Flurbiprofen had only weak stereoselectivity in HSA, and ketoprofen had no stereoselectivity at all. Scatchard curves showed that all the three chiral drugs had two types of binding sites in HSA.

Enantioselective Pharmacokinetics of Ibuprofen and Involved Mechanisms

Although dexibuprofen (S-ibuprofen) was marketed in Austria and Switzerland, the racemate at various formulations is still extensively used worldwide, and there are no indications that the racemate will be replaced by the single enantiomer. Thus, elucidation of the characteristics and involved mechanisms of the chiral pharmacokinetics of racemic ibuprofen is of special importance for the understanding of the pharmacological and toxicological consequences, and for prediction of the clinically potential drug interactions and influence of the pathological states. Stereoselective pharmacokinetics and metabolism are common features for chiral nonsteroidal antiinflammatory drugs (NSAIDs) and especially for 2-arylpropionic acid derivatives characterized with a chiral center adjacent to the carboxyl group. Although the enantioselective pharmacokinetic characteristics of different NSAIDs should be treated case by case, they share similar mechanisms underlying the protein binding, metabolism and chiral inversion. Ibuprofen was the most extensively researched drug in terms of chiral characteristics and mechanisms. Therefore, elucidation of the mechanisms derived from research on ibuprofen may provide better understanding and prediction of other chiral drugs. This article attempts to elucidate the chiral pharmacokinetics and involved mechanisms of ibuprofen in comparison with other NSAIDs based on recent developments. Topics on history of ibuprofen, enantioselective analysis method, absorption, protein binding, conventional metabolism, metabolic chiral inversion, gene polymorphism, and biochemical developments were included. It is worth mentioning that some underlying biochemical mechanisms, especially for the metabolic chiral inversion and ethnic differences still remain to be seen. Further research is required to develop human-resourced researching model and to provide more evidence concerning the site of inversion, species variation, CYP450 gene polymorphisms, and biochemical mechanisms.

Characterization and quantification of metabolites of racemic ketoprofen excreted in urine following oral administration to man by1H-NMR spectroscopy, directly coupled HPLC-MS and HPLC-NMR, and circular dichroism

The identity of the human metabolites of ketoprofen (2-(3-benzoylphenyl)-propanoic acid) excreted via urine was investigated after a single oral dose of the racemic drug. Drug metabolites were concentrated and partially purified from urine using solid-phase extraction chromatography before separation and identification by directly coupled HPLC-MS and HPLC-NMR. The metabolites identified were the ester glucuronides of the parent drug and its phase I metabolites, 2-[3-(3-hydroxybenzoyl)phenyl]-propanoic acid, 2-[3-(4-hydroxybenzoyl)phenyl]-propanoic acid and 2-[3-(hydroxy(phenyl)methyl)phenyl]-propanoic acid, the latter formed by reduction of the ketone group of ketoprofen. In addition, two novel minor metabolites were identified as the ether glucuronides of 2-[3-(3-hydroxybenzoyl)phenyl]-propanoic acid and 2-[3-(4-hydroxybenzoyl)phenyl]-propanoic acid. These conjugates were all observed as diastereoisomeric pairs of unequal proportions. Purification of these metabolites by preparative chromatography allowed stereochemistry assignments. Metabolites were quantified by 1H-NMR spectroscopy after spectral simplification achieved by hydrolysis of the conjugates.

Drug disposition in three dimensions: an update on stereoselectivity in pharmacokinetics

Many marketed drugs are chiral and are administered as the racemate, a 50:50 combination of two enantiomers. Pharmacodynamic and pharmacokinetic differences between enantiomers are well documented. Because of enantioselectivity in pharmacokinetics, results of in vitro pharmacodynamic studies involving enantiomers may differ from those in vivo where pharmacokinetic processes will proceed. With respect to pharmacokinetics, disparate plasma concentration vs time curves of enantiomers may result from the pharmacokinetic processes proceeding at different rates for the two enantiomers. At their foundation, pharmacokinetic processes may be enantioselective at the levels of drug absorption, distribution, metabolism and excretion. In some circumstances, one enantiomer can be chemically or biochemically inverted to its antipode in a unidirectional or bidirectional manner. Genetic consideration such as polymorphic drug metabolism and gender, and patient factors such as age, disease state and concomitant drug intake can all play a role in determining the relative plasma concentrations of the enantiomers of a racemic drug. The use of a nonstereoselective assay method for a racemic compound can lead to difficulties in interpretation of data from, for example, bioequivalence or dose/concentration vs effect assessments. In this review data from a number of representative studies involving pharmacokinetics of chiral drugs are presented and discussed.

Dexketoprofen-induced antinociception in animal models of acute pain: Synergy with morphine and paracetamol

The antinociceptive activity of dexketoprofen was studied in mice using the acetic acid writhing test (acute tonic pain), the tail flick test (acute phasic pain) and the formalin assay (inflammatory pain). Isobolographic analysis was used to study the antinociceptive interactions between morphine and paracetamol co-administered with dexketoprofen. In the writhing test, the intraperitoneal administration of dexketoprofen or ketoprofen resulted in parallel dose-response curves with equal efficacy, but higher relative potency for dexketoprofen. In the tail flick test, the curves were parallel with similar efficacy and potency. The administration of morphine or paracetamol in both tests resulted in dose-response curves not parallel with that of dexketoprofen, which showed a potency between morphine and paracetamol. In the formalin assay, the antinociceptive activity of morphine during phase I was 122, 295 and 1695 times higher than dexketoprofen, ketoprofen and paracetamol, respectively. Isobolographic analysis demonstrated that the combination of sub-analgesic doses of dexketoprofen with morphine or with paracetamol was strongly synergic in all three tests. Synergistic drug combinations should improve effective pharmacological treatment of pain, minimizing drug specific adverse effects. These findings are undoubtedly worthy of additional controlled clinical trials in severe pain syndromes.

Role of racemization in optically active drugs development

U.S. Food and Drug Administration issues certain guidelines for marketing of optically active drugs as some enantiomers racemize into human body, leading to the generation of other antipodes, which may be toxic or ballast to the human beings. Moreover, racemization reduces the administrated dosage concentration as optically active enantiomer converted into its inactive counter part. Therefore, the study of racemization of such type of drugs is an important and urgent need of today. This article describes in vitro and in vivo racemization of optically active drugs. The racemization process of various optically active drugs has been discussed considering the effect of different variables i.e. pH, temperature, concentration of the drug, ionic concentration, etc. Attempts have also been made to discuss the mechanisms of racemization. Besides, efforts have been made to suggest the safe dosages of such type of drugs too.

Study on the mechanism of photosensitive dermatitis caused by ketoprofen in the guinea pig

To investigate the mechanism on photosensitive dermatitis caused by ketoprofen (KP) in humans, the following experiments were performed by topical application on guinea pigs. The phototoxicity study involving treatment with 10% solution of KP, its enantiomers (R-KP and S-KP), loxoprofen, and flurbiprofen revealed no phototoxic reactions. In the photoallergenicity study, KP and its enantiomers (0.5-2% solution) induced skin reaction at all dosages; however, loxoprofen and flurbiprofen (1-5% solution) did not induce such a photoallergenic reaction. These results suggest that the chemical structure of the benzophenone chromophore in KP would be one of the important factors for induction of the photoallergy since both loxoprofen and flurbiprofen do not possess this structure and hence lack photoallergenic potential. Furthermore, to assess time profiles of KP concentration in the skin and plasma, guinea pigs received a repeated topical application of R-KP and S-KP at a dosage of 40 mg/kg over a period of 3 days. Plasma KP concentrations were extremely low as compared to skin KP concentrations and were not detected at 72 h after the final dosing. At 24 h after the final dosing, KP concentrations in the skin with R-KP and S-KP treatment were 187.4 and 254.7 microg/g, respectively, and their half-lives were 80.5 and 84.4 h, respectively. KP concentrations at 336 h after final dosing were 11.3 microg/g for R-KP and 15.7 microg/g for S-KP treatment. The acylglycerol-combined KP concentrations at 336 h were 2% or less as compared to KP concentrations with R-KP and S-KP treatment. There were no differences in KP concentrations in the skin between R-KP and S-KP and in combined KP concentrations between the enantiomers. The present study indicates that photosensitive dermatitis after topical application of KP in humans, caused by photoallergenicity and not phototoxicity, can be reproduced in the animal testing, and suggests that the skin reaction may be caused by the long period of retention of KP in the skin.

Renal d-Amino Acid Oxidase Mediates Chiral Inversion ofNG-Nitro-d-arginine

N(G)-nitro-d-arginine (d-NNA), i.v. injected into rats, produced a pressor response, and was presumed to act via chiral inversion into N(G)-nitro-l-arginine (l-NNA), an inhibitor of nitric oxide synthase. We examined the possible role of renal d-amino acid oxidase (DAAO) in the chiral inversion of d-NNA to l-NNA. In pentobarbital-anesthetized rats, l-NNA was detected via capillary electrochromatography in the blood immediately after i.v. injection of d-NNA. The time course of appearance of l-NNA paralleled the increase in blood pressure elicited by d-NNA. Unilateral renal ligation partially, and bilateral ligation completely, blocked the pressor response as well as the conversion of d-NNA to l-NNA. Furthermore, injection into conscious rats of sodium benzoate, a selective DAAO inhibitor, completely blocked the pressor response to naive d-NNA, but not pressor response to d-NNA preincubated with homogenates of the kidney. Homogenates of the kidneys, liver (lesser degree), and brain (much lesser degree) converted d-NNA to l-NNA, and the chiral inversion was blocked by the addition of benzoate. Moreover, d-NNA chiral inversion correlates with the activity of DAAO. Our results reveal a novel pathway of chiral inversion of d-amino acids where the renal DAAO plays an essential role that accounts for the biological activity of d-NNA.

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.

The stereospecificity of flobufen metabolism in isolated guinea pig hepatocytes

BACKGROUND

Flobufen (F) is an original nonsteroidal anti-inflammatory drug with one center of chirality. 4-Dihydroflobufen (DHF), compound with two chiral centers, is the main metabolite of F in microsomes and cytosol in all standard laboratory animals. This work describes the biotransformation of F enantiomers and DHF stereoisomers in isolated male guinea pig hepatocytes. Guinea pigs were chosen with respect to similarities in F metabolism as in Man found earlier. R-F, S-F, (2R;4S)-DHF, (2S;4R)-DHF, (2S;4S)-DHF and (2R;4R)-DHF, structurally very similar compounds, served as substrates in order to observe their interaction with enzymes. Stereospecificity of the respective enzymes was studied in vitro, using hepatocytes monolayer. Chiral HPLC using R,R-ULMO column as chiral stationary phase was used for detection and quantitation of metabolites.

RESULTS

(2R;4S)-DHF and (2S;4S)-DHF were the principle stereoisomers detected after incubation with rac-F, R-F and S-F. The ratio of (2R;4S)-DHF/(2S;4S)-DHF ranged from 1.1 to 2.4 depending on the substrate used. (2R;4S)-DHF was the major stereoisomer found after incubation with (2S;4S)-DHF and (2R;4R)-DHF. (2S;4S)-DHF was the principle stereoisomer found after incubation with (2R;4S)-DHF and (2S;4R)-DHF. Besides DHF stereoisomers, other metabolites (M-17203, UM-1 and UM-2) were also detected after incubation of hepatocytes monolayer with F. Interestingly, these metabolites were not found in incubation of all F forms and DHF with fresh liver homogenate.

CONCLUSIONS

Different activities and stereospecificities of the respective enzymes were observed for each substrate in primary culture of hepatocytes. Cell integrity is crucial for formation of secondary metabolites M-17203, UM-1 and UM-2.

Reduction of flobufen in pig hepatocytes: effect of pig breed (domestic, wild) and castration

Knowledge of the biotransformation processes of veterinary drugs and food supplements in food-producing animals is increasingly important. Residual levels of parent compounds or their metabolites in food of animal origin may differ with the breed, breeding conditions, and gender of animals. The nonsteroidal antiinflammatory drug flobufen, 4-(2',4'-difluorobiphenyl-4-yl)-2-methyl-4-oxobutanoic acid (racemic or its individual enantiomers) was used as a model to evaluate differences in activity, stereoselectivity, and stereospecificity of reductases in primary cultures of hepatocytes from intact male or castrated male domestic pigs (Sus scrofa domestica) or male wild pig (Sus scrofa scrofa). Time-dependent consumption of flobufen enantiomers and formation of dihydroflobufen (DHF) diastereoisomers as their principal metabolites in hepatocytes were measured using chiral HPLC. Flobufen reduction in hepatocytes from all three experimental groups of animals was stereoselective ((+)-R-flobufen was predominantly metabolized) and stereospecific (2R;4S-DHF and 2S;4S-DHF diastereoisomers were preferentially formed). Flobufen reductases activity in male domestic pigs was 30 times higher compared to castrated pigs. Flobufen reductases activity was similar in domestic and wild pigs. The stereospecificity and stereoselectivity of DHF production did not significantly differ with breed or castration of animal. Chiral inversion of flobufen enantiomers was also studied and differences between castrated and intact male pigs were seen.

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.

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.

Stereospecificity and stereoselectivity of flobufen metabolic profile in male rats in vitro and in vivo: phase I of biotransformation

Flobufen (F) is the original nonsteroidal antiinflammatory drug (NSAID) containing two enantiomers. The aim of this investigation was to elucidate the biotransformation pathway of F at chiral level in phase I of biotransformation. Stereoselectivity and stereospecificity of the respective enzymes were studied in male rats in vitro (microsomal and cytosolic fractions, hepatocytes suspension) and in vivo. The rac-F, (+)-R-F and (-)-S-F were used as substrates. Amounts of F enantiomers, 4-dihydroflobufen diastereoisomers (DHF) and other metabolites (M-17203, UM) were determined with a chiral HPLC method in two chromatographic runs on R,R-ULMO and allyl-terguride bonded columns. Stereoselective biotransformation of the two enantiomers of F was observed at all tested levels and significant bidirectional chiral inversion of enantiomers of F was observed in hepatocytes. Mean enantiomeric ratios of F concentrations (S-/R-), after rac-F incubations, ranging from 1.09 in cytosolic fraction to 18.23 in hepatocytes. Stereospecificity of the respective F reductases was also observed. (2R;4S)-DHF and (2S;4S)-DHF are the principal metabolites of F in microsomes and hepatocytes. Neither DHF diastereoisomers nor M-17203 were found in cytosolic fraction. Only the nonchiral metabolite, M-17203, was found in all urine and feces samples after oral administration of F.

Disposition of suprofen enantiomers in the cat

Suprofen (SPF) is a non-steroidal anti-inflammatory drug (NSAID), which belongs to the 2-arylpropionic acids subclass. As a result of their chiral characteristics, these compounds have shown a marked enantioselective behaviour with a high degree of interspecies variation. They are mainly eliminated by glucuronidation. Plasma, biliary and urine disposition of SPF was investigated in the cat after intravenous administration of the racemate (dose 2 mg/kg). Both enantiomers exhibited similar disposition profiles in plasma with no evidence of chiral inversion. During bile sampling time, recovered acylglucuronides of R (-) and S (+) SPF were less than 1% of the total dose administered. Only free SPF was recovered in the urine, representing 0.12% of the administered racemic SPF dose. The results indicate that neither chiral inversion nor glucuronidation predominate in SPF disposition in cats.

Clinical Pharmacokinetics of Dexketoprofen

Dexketoprofen trometamol is a water-soluble salt of the dextrorotatory enantiomer of the nonsteroidal anti-inflammatory drug (NSAID) ketoprofen. Racemic ketoprofen is used as an analgesic and an anti-inflammatory agent, and is one of the most potent in vitro inhibitors of prostaglandin synthesis. This effect is due to the (S)-(+)-enantiomer (dexketoprofen), while the (R)-(-)-enantiomer is devoid of such activity. The racemic ketoprofen exhibits little stereoselectivity in its pharmacokinetics. Relative bioavailability of oral dexketoprofen (12.5 and 25mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50mg, respectively), as measured in all cases by the area under the concentration-time curve values for (S)-(+)-ketoprofen. Dexketoprofen trometamol, given as a tablet, is rapidly absorbed, with a time to maximum plasma concentration (tmax) of between 0.25 and 0.75 hours, whereas the tmax for the (S)-(+)-enantiomer after the racemic drug, administered as tablets or capsules prepared with the free acid, is between 0.5 and 3 hours. The drug does not accumulate significantly when administered as 25mg of free acid 3 times daily. The profile of absorption is changed when dexketoprofen is ingested with food, reducing both the rate of absorption (tmax) and the maximal plasma concentration. Dexketoprofen is strongly bound to plasma proteins, particularly albumin. The disposition of ketoprofen in synovial fluid does not appear to be stereoselective. Dexketoprofen trometamol is not involved in the accumulation of xenobiotics in fat tissues. It is eliminated following extensive biotransformation to inactive glucuroconjugated metabolites. No (R)-(-)-ketoprofen is found in the urine after administration of dexketoprofen, confirming the absence of bioinversion of the (S)-(+)-enantiomer in humans. Conjugates are excreted in urine, and virtually no drug is eliminated unchanged. The analgesic efficacy of the oral pure (S)-(+)-enantiomer is roughly similar to that observed after double dosages of the racemic compound. At doses above 7mg, dexketoprofen was significantly superior to placebo in patients with moderate to severe pain. A dose-response relationship between 12.5 and 25mg could be seen in the time-effects curves, the superiority of the 25mg dose being more a result of an extended duration of action than of an increase in peak analgesic effect. A plateau in the analgesic activity of dexketoprofen trometamol at the 25mg dose is suggested. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol. The drug was well tolerated.

Validation of a high-performance liquid chromatographic method for the determination of ibuprofen enantiomers in plasma of broiler chickens

To characterise the pharmacokinetic properties of each enantiomer of ibuprofen in broiler chickens, a stereospecific HPLC method based on a alpha1-acid glycoprotein bonded chiral stationary phase has been validated. S-(+)-naproxen was used as internal standard. Enantiomers of ibuprofen and S-(+)-naproxen were baseline separated using a mobile phase consisting of 0.1 M phosphate buffer pH = 7 and 0.4% 2-propanol. The method is precise, specific, accurate and reproducible. Recoveries were higher than 80% and the limits of quantification for R-(-)- and S-(+)-ibuprofen were 1.16 and 1.37 microg ml(-1), respectively. The method seemed suitable for the pharmacokinetic studies of ibuprofen in chickens.

Differential effects of spinal (R)-ketoprofen and (S)-ketoprofen against signs of neuropathic pain and tonic nociception: evidence for a novel mechanism of action of (R)-ketoprofen against tactile allodynia

The spinal activity of racemic ketoprofen and its enantiomers in models of neuropathic and tonic pain was explored in rats. Tactile allodynia and thermal hyperalgesia were induced by tight ligation of the L(5)/L(6) spinal nerves. Tonic pain was modeled by the formalin-induced flinch response. The spinal injection of (S)-ketoprofen alone or of morphine alone did not produce antiallodynic activity. A 1:1 combination of these drugs produced a robust dose-dependent antiallodynic action, consistent with previous observations where (S)-ketorolac combined with morphine also produced antiallodynia. (R)-ketoprofen given alone spinally produced a dose-dependent antiallodynia, but its activity was not augmented by spinal morphine. Conversely, (S)-ketoprofen, but not (R)-ketoprofen, blocked the second phase of the formalin-induced flinch response; neither enantiomer significantly blocked phase one of the formalin response. Again, (S)-, but not (R)-ketoprofen, interacted synergistically with spinal morphine in suppressing the phase II formalin response. These results are consistent with a spinal COX inhibitory action of (S)-ketoprofen. These results also point to a novel, as yet undefined, mechanism of action of (R)-ketoprofen against signs of neuropathic pain that does not appear to involve COX inhibition. The ability to modulate tactile allodynia is of special interest as this represents an aspect of clinical neuropathic pain that is very difficult to treat adequately.

Stereospecific pharmacokinetics and toxicodynamics of ketorolac after oral administration of the racemate and optically pure enantiomers to the rat

To determine the stereospecific pharmacokinetics and gastrointestinal permeability (GI) changes (surrogate measures of toxicity) in the rat following oral administration of S, R, and racemic ketorolac (KT), optically pure enantiomers (S and R 2.5 mg/kg), and racemic KT (5 mg/kg) were administered orally to male Sprague-Dawley rats and plasma samples were collected for 6 h post-dose for pharmacokinetic assessments. KT-induced changes in GI permeability were assessed using sucrose and 51Cr-EDTA as markers of gastroduodenal and distal intestinal permeability, respectively. After the racemate, R-KT was predominant in plasma (AUC S/R, 0.45). No significant differences in pharmacokinetic indices were evident following administration of the racemate as compared with individual enantiomers. In plasma, there was only negligible S-KT after administration of R-KT. After S-KT, on the other hand, AUC of R-KT was found to be 6.7% of that of S-KT. Both permeability markers showed considerable interanimal variability. Gastroduodenal permeability was significantly increased from baseline by the racemate but not by either of the two enantiomers administered alone. Permeability to 51Cr-EDTA was not significantly increased above baseline for any of the treatments. The plasma concentration of R-KT found after administration of S-KT may be from the < 2% chiral impurity which appears magnified due to its slower clearance as compared with its antipode. There is no evidence of a pharmacokinetic interaction between the enantiomers. Since 2.5 mg/kg S-KT is somewhat less toxic on the gastroduodenum than 5 mg/kg racemate, it may be a safer alternative to the latter, at least in the rat model.

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.

Bioavailability of racemic ketoprofen in healthy horses following rectal administration

Ketoprofen (KTP) is a chiral non-steroidal anti-inflammatory drug (NSAID) of the propionic acid class, approved by the FDA for the allevation of pain associated with musculoskeletal disorders in horses. The present study was designed to examine the bioavailability of ketoprofen enantiomers after rectal administration of the racemate to healthy horses. One gram of racemic ketoprofen was injected intravenously and administered rectally as a fat based suppository in a cross-over design study (n = 4). Blood samples were analysed for KTP enantiomers using HPLC. After IV administration, the S(+) enantiomer concentrations in plasma were higher than the R(-) enantiomer concentrations and the AUC(0-12 h) for the S(+) enantiomer was significantly higher than for the R(-) enantiomer. Following rectal administration C(max) and AUC(0-12 h) were significantly higher for the S(+) than for the R(-) enantiomer. Bioavailability after rectal administration was low. Since there was no significant difference in bioavailability between the two enantiomers, it is assumed that no pre-systemic inversion from R(-) to S(+) occurred after rectal administration of racemic KTP to horses.

Epimerization of moxalactam by albumin and simulation of in vivo epimerization by a physiologically based pharmacokinetic model

We investigated the mechanism of epimerization (R to S or S to R) of moxalactam in serum of rats, dogs, and humans. The epimerization of moxalactam occurred in the serum of these animals, but not in the serum filtrate. The albumin fraction of human serum purified by gel filtration catalysed the epimerization of moxalactam at an identical rate to serum, but other fractions (i.e., lipoproteins and globulins) showed slower epimerization. alpha 1-acid glycoprotein, which was eluted in the same fraction with albumin by G-200 gel filtration, did not epimerize moxalactam. The presence of 2 mM warfarin decreased the binding of R- and S-moxalactam and decreased the epimerization of moxalactam in human serum. These results demonstrate moxalactam was epimerized on the warfarin binding site on albumin in serum. Additionally, a physiologically based pharmacokinetic model shows that the epimerization of moxalactam after administration in dogs is simulated by the epimerization in serum.

HPLC on Chiralcel OJ-R for enantiomer separation and analysis of ketoprofen, from horse plasma, as the 9-aminophenanthrene derivative

Racemic ketoprofen is a non-steroidal anti-inflammatory drug used to treat musculoskeletal and colic conditions in horses. The enantioselective chiral inversion of ketoprofen administered to horses has been studied by use of cellulose tris(4-methylbenzoate), also known as Chiralcel OJ-R, as chiral stationary phase; acetonitrile - 0.02 M perchlorate buffer (pH 2.0)-methanol, 60:15:25 (v/v/v) was used as mobile phase. Before chromatography, to effect adequate chiral interaction with the chiral stationary phase ketoprofen was derivatized with 9-aminophenanthrene, under acid conditions, after solid-phase (C18) extraction and then liquid-liquid extraction, to ensure effective removal of endogenous plasma materials. The 9-aminophenanthrene derivative of S-ibuprofen was used as internal standard. The enantiomers of ketoprofen were separated to baseline (Rs = 6.44, alpha = 1.76) within a short analysis time. The results indicate that the bio-inversion of R-ketoprofen to the S isomer is significant in equine species. However, considerable differences in pharmacokinetic parameters were observed, indicating large inter-animal variation.