Pharmacokinetics of enantiomers of chiral non-steroidal anti-inflammatory drugs

R-ketorolac ameliorates cancer-associated cachexia and prolongs survival of tumour-bearing mice

BACKGROUND

Cancer-associated cachexia (CAC) is a debilitating syndrome associated with poor quality of life and reduced life expectancy of cancer patients. CAC is characterized by unintended body weight reduction due to muscle and adipose tissue loss. A major hallmark of CAC is systemic inflammation. Several non-steroidal anti-inflammatory drugs (NSAIDs) have been suggested for CAC treatment, yet no single medication has proven reliable. R-ketorolac (RK) is the R-enantiomer of a commonly used NSAID. The effect of RK on CAC has not yet been evaluated.

METHODS

Ten- to 11-week-old mice were inoculated with C26 or CHX207 cancer cells or vehicle control (phosphate-buffered saline [PBS]). After cachexia onset, 2 mg/kg RK or PBS was administered daily by oral gavage. Body weight, food intake and tumour size were continuously measured. At study endpoints, blood was drawn, mice were sacrificed and tissues were excised. Immune cell abundance was analysed using a Cytek® Aurora spectral flow cytometer. Cyclooxygenase (COX) activity was determined in lung homogenates using a fluorometric kit. Muscle tissues were analysed for mRNA and protein expression by quantitative real-time PCR and western blotting analysis, respectively. Muscle fibre size was determined on histological slides after haematoxylin/eosin staining.

RESULTS

Ten-day survival rate of C26-bearing animals was 10% while RK treatment resulted in a 100% survival rate (P = 0.0009). Chemotherapy resulted in a 10% survival rate 14 days after treatment initiation, but all mice survived upon co-medication with RK and cyclophosphamide (P = 0.0001). Increased survival was associated with a protection from body weight loss in C26 (-0.61 ± 1.82 vs. -4.48 ± 2.0 g, P = 0.0004) and CHX207 (-0.49 ± 0.33 vs. -2.49 ± 0.93 g, P = 0.0003) tumour-bearing mice treated with RK, compared with untreated mice. RK ameliorated musculus quadriceps (-1.7 ± 7.1% vs. -27.8 ± 8.3%, P = 0.0007) and gonadal white adipose tissue (-18.8 ± 49% vs. -69 ± 15.6%, P = 0.094) loss in tumour-bearing mice, compared with untreated mice. Mechanistically, RK reduced circulating interleukin-6 (IL-6) concentrations from 334 ± 151 to 164 ± 123 pg/mL (P = 0.047) in C26 and from 93 ± 39 to 35 ± 6 pg/mL (P = 0.0053) in CHX207 tumour-bearing mice. Moreover, RK protected mice from cancer-induced T-lymphopenia (+1.8 ± 42% vs. -49.2 ± 12.1% in treated vs. untreated mice, respectively). RK was ineffective in ameliorating CAC in thymus-deficient nude mice, indicating that the beneficial effect of RK depends on T-cells.

CONCLUSIONS

RK improved T-lymphopenia and decreased systemic IL-6 concentrations, resulting in alleviation of cachexia and increased survival of cachexigenic tumour-bearing mice, even under chemotherapy and independent of COX inhibition. Considering its potential, we propose that the use of RK should be investigated in patients suffering from CAC.

Narrative review shows that the short-term use of ketorolac is safe and effective in the management of moderate-to-severe pain in children

In June 2013, the European Medicine Agency recommended limiting codeine use in paediatric patients, creating a void in managing moderate pain. We reviewed the literature published in English (1985-June 2017) on the pharmacokinetic, pharmacodynamic and safety profile of ketorolac, a possible substitute for codeine and opioids, for treating moderate-to-severe pain. We found that gastrointestinal side effects were mainly reported with prolonged use, significant bleeding was reported in adenotonsillectomy, and adverse renal effects appeared to be limited to patients with specific coexisting risk factors.

CONCLUSION

The short-term use of ketorolac appears to be safe for children in many situations.

Enantiomer-specific ketorolac pharmacokinetics in young women, including pregnancy and postpartum period

Racemic ketorolac clearance (CL) is significantly higher at delivery, but S-ketorolac disposition determines the analgesic effects. The aim of this study was to investigate the effect of pregnancy and postpartum period on enantiomer-specific (S and R) intravenous (IV) ketorolac pharmacokinetics (PKs). Data in women shortly following cesarean delivery (n=39) were pooled with data in a subgroup of these women that was reevaluated in the later postpartum period (postpartum group, n=8/39) and with eight healthy female volunteers. All women received single IV bolus of 30 mg ketorolac tromethamine. Five plasma samples were collected at 1, 2, 4, 6, and 8 hours and plasma concentrations were determined using high performance liquid chromatography. Enantiomer-specific PKs were calculated using PKSolver. Unpaired analysis showed that distribution volume at steady state (Vss, L/kg) for S- and R-ketorolac was significantly higher in women shortly following cesarean delivery (n=31) compared to postpartum group (n=8) or to healthy female volunteers (n=8). CL, CL to body weight, and CL to body surface area (CL/BSA) for S- and R-ketorolac were also significantly higher in women following delivery. In addition, S/R-ketorolac CL/BSA ratio was significantly higher at delivery. Paired PK analysis in eight women shortly following delivery and in postpartum group showed the same pattern. Finally, the simultaneous increase in CL and Vss resulted in similar estimates for elimination half-life in both unpaired and paired analysis. In conclusion, pregnancy affects S-, R-, and S/R-ketorolac disposition. This is of clinical relevance since S-ketorolac (analgesia) CL is even more increased compared to R-ketorolac CL, and S/R-ketorolac CL ratio is higher following delivery compared to postpartum period or to healthy female volunteers.

Drug metabolism and pharmacokinetics

In this article, aspects of absorption, distribution, metabolism, and excretion have been described bearing in mind the pathogenesis of allergic diseases and their possible therapeutic opportunities. The importance of the routes of administration of the different therapeutic groups has been emphasized. The classical aspects of drug metabolism and disposition related to oral administration have been reviewed, but special emphasis has been given to intranasal, cutaneous, transdermal, and ocular administration as well as to the absorption and the subsequent bioavailability of drugs. Drug-metabolizing enzymes and transporters present in extrahepatic tissues, such as nasal mucosa and the respiratory tract, have been particularly discussed. As marketed antiallergic drugs include both racemates and enantiomers, aspects of stereoselective absorption, distribution, metabolism, and excretion have been discussed. Finally, a new and promising methodology, microdosing, has been presented, although it has not yet been applied to drugs used in the treatment of allergic diseases.

Stereoselective glucuronidation and hydroxylation of etodolac by UGT1A9 and CYP2C9 in man

1. In vitro metabolic studies with etodolac were performed. S- and R-etodolac were converted to the acylglucuronide and hydroxylated metabolites by UDP-glucuronosyltransferase (UGT) and cytochrome P450 in microsomes. However, the stereoselectivities of UGT and P450 for the isomers were opposite. S-etodolac was glucuronidated preferentially than R-etodolac by UGT. In contrast, R-etodolac was hydroxylated preferentially than S-etodolac by P450. 2. Of several human P450 enzymes, CYP2C9 had the greatest activity for hydroxylation of R-etodolac. Sulfaphenazole, an inhibitor of CYP2C9, and anti-CYP2C9 antibody inhibited the hydroxylation of R-etodolac in human liver microsomes. CYP2C9 therefore contributes to the stereoselective hydroxylation of R-etodolac. 3. Of several human UGT enzymes, UGT1A9 had the greatest activity for glucuronidation of S-etodolac. Propofol and thyroxine, inhibitors of UGT1A9, inhibited the glucuronidation of S-etodolac in human liver microsomes. Therefore, UGT1A9 is mainly responsible for the stereoselective glucuronidation of S-etodolac. 4. Because S-etodolac was metabolized more rapidly than R-etodolac in human cryopreserved hepatocytes, the stereoselectivities of UGT1A9 for etodolac substantially influenced the overall metabolism of S- and R-etodolac in man.

Chiral inversion of RS-8359: a selective and reversible MAO-A inhibitor via oxido-reduction of keto-alcohol

RS-8359, (+/-)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]-pyrimidine is a selective and reversible MAO-A inhibitor. The (S)-enantiomer of RS-8359 has been demonstrated to be inverted to the (R)-enantiomer after oral administration to rats. In the current study, we investigated the chiral inversion mechanism and the properties of involved enzymes using rat liver subcellular fractions. The 7-hydroxy function of RS-8359 was oxidized at least by the two different enzymes. The cytosolic enzyme oxidized enantiospecifically the (S)-enantiomer with NADP as a cofactor. On the other hand, the microsomal enzyme catalyzed more preferentially the oxidation of the (S)-enantiomer than the (R)-enantiomer with NAD as a cofactor. With to product enantioselectivity of reduction of the 7-keto derivative, it was found that only the alcohol bearing (R)-configuration was formed by the cytosolic enzyme with NADPH and the microsomal enzyme with NADH at almost equal rate. The reduction rate was much larger than the oxidation rate of 7-hydroxy group. The results suggest that the chiral inversion might occur via an enantioselectivity of consecutive two opposing reactions, oxidation and reduction of keto-alcohol group. In this case, the direction of chiral inversion from the (S)-enantiomer to the (R)-enantiomer is governed by the enantiospecific reduction of intermediate 7-keto group to the alcohol with (R)-configuration. The enzyme responsible for the enantiospecific reduction of the 7-keto group was purified from rat liver cytosolic fractions and identified as 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) via database search of peptide mass data obtained by nano-LC/MS/MS.

A novel method for assessing inhibition of ibuprofen chiral inversion and its application in drug discovery

An inhibition assay to assess the potential for chiral inversion of compounds was developed using R(-)-ibuprofen as the probe substrate. Inhibition of the chiral inversion of R(-)-ibuprofen by structurally similar compounds in cyropreserved rat hepatocytes was studied using chiral HPLC and LC/MS methods for the chromatographic separation and detection of enantiomers. Concept validation of this assay was performed with three commercially available compounds and four Pfizer compounds. The results of these studies demonstrated that compounds that are structurally similar to ibuprofen inhibited the formation of S(+)-ibuprofen, suggesting that they may undergo similar enzymatic chiral inversion pathways or compete for the same enzyme active sites. Additionally, an application of this assay in early drug discovery for a specific class of compounds was demonstrated. Thirty-three in-house compounds were screened for their chiral inversion potential utilizing this assay to investigate the structure activity relationship (SAR) for this class of compounds.

Stereoselective Taurine Conjugation of (R)-Benoxaprofen Enantiomer in Rats: In Vivo and in Vitro Studies Using Rat Hepatic Mitochondria and Microsomes

PURPOSE

Identify (R)-BOP-T in rat bile after administration of (R)-BOT over a 12 h period.

METHODS

Each benoxaprofen (BOP) enantiomer was administered i.v. to bile duct-cannulated rats at a dose of 5 mg/kg. The optical isomers of BOP and its metabolites in plasma, urine, and bile were quantified using a chiral HPLC column. The amounts of BOP glucuronide (BOP-G), BOP taurine conjugate (BOP-T), and BOP enantiomers excreted into the bile over 12 h after administration of (R)-BOP were as follows: (R)-BOP-G and (S)-BOP-G, 2.1 +/- 0.5 and 6.2 +/- 1.4% of the dose; (R)-BOP-T and (S)-BOP-T, 5.6 +/- 1.8 and 0.7 +/- 0.3% of the dose; (R)-BOP and (S)-BOP, 0.7 +/- 0.1 and 1.7 +/- 0.2% of the dose, respectively, whereas after (S)-BOP administration, (S)-BOP-G and (S)-BOP were mainly excreted into the bile (14.3 +/- 1.8 and 3.0 +/- 0.4% of the dose, respectively). Only after (R)-BOP administration was the taurine conjugate of BOP found in the bile, and the configuration was R. BOP-T could not be found in the bile after (S)-BOP administration. To investigate the stereoselectivity of the conjugation enzymes responsible for BOP-T formation, in vitro studies were performed using rat hepatic organelles.

RESULTS

When (R)-BOP was used as a substrate, rat hepatic mitochondrial and microsomal fractions exhibited stereoselective BOP-T formation activity, with microsomal activity approximately 3.0 times greater than that of the mitochondria. That of (S)-BOP was approximately 2.1. Mean (R)/(S) ratios of BOP enantiomer for BOP-T formation in the mitochondrial and microsomal incubations were approximately 1.7 and 2.4, respectively.

CONCLUSION

Although in the in vivo studies, only (R)-BOP-T originated from (R)-BOP was found in the bile, the configuration of BOP-T formed by the incubations of (R)-BOP or (S)-BOP with rat hepatic mitochondria or microsomes was S for both.

Enantiospecific disposition of pranoprofen in beagle dogs and rats

The pharmacokinetic characteristics of pranoprofen enantiomer were examined and compared with the disposition of the corresponding isomer after the administration of racemic pranoprofen to beagle dogs and rats. The plasma levels of (+)-(S)-isomer were significantly higher than those of (-)-(R)-isomer in dogs and rats by either intravenous or oral administration. Although the oral bioavailability and absorption rate constant between the (-)-(R)- and (+)-(S)-form was the same, the elimination rate constant of the (+)-(S)-form was significantly lower than that of the (-)-(R)-form in both dogs and rats. This discrepancy can be explained on the basis of differences in protein binding and the metabolism of the two enantiomers. The (-)-(R)-isomer was predominantly conjugated depending on its higher free plasma level and its faster metabolic rate than the (+)-(S)-form, and thus was excreted more rapidly in the urine and bile in the form of pranoprofen glucuronide. Furthermore, a (-)-(R)- to (+)-(S)-inversion occurred to the extent of 14% in beagle dogs, but not in rats. This chiral inversion might be an important factor in the slow elimination of the (+)-(S)-form in dogs. The most efficient organ for chiral inversion was the liver, followed by kidney and intestine.

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.

Chiral inversion of (R)-ketoprofen: influence of age and differing physiological status in dairy cattle

The chiral inversion of ketoprofen has been previously demonstrated in cattle, but no studies have been performed on different ages and metabolic situations in the animals. The aim of this work was to study any modifications of the stereoconversion of ketoprofen that occur by reason of age, lactation or gestation in dairy cows. Holando Argentino cattle were divided into three groups: 8 cows in early lactation, 8 pregnant cows and 8 newborn calves. Four animals from each group received the enantiomer R-(-)-ketoprofen by intravenous administration; the other four animals received the S-(+) enantiomer, all at doses of 0.5 mg/kg. Blood samples were collected at standardized times after dosing and assayed for ketoprofen by high-performance reversed-phase liquid chromatography (HPLC). The percentage inversion of R-(-)-ketoprofen to S-(+)-ketoprofen was 50.5% (SD +/- 2.4) in the preruminants, 33.3% (SD +/- 1.7) in cows in early lactation and 26.0% (SD +/- 5.1) in cows in gestation. These results indicate a differing enantioselective metabolic behaviour for one compound in one species under different physiological situations.

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.

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.

Bioinversion of ibuprofen enantiomers after administration in dogs: estimation of a novel index

This study compares the pharmacokinetics and bioinversion of two chemical forms of ibuprofen administered intravenously or orally. Dogs were given the free acid form of the S(+) isomer p.o. or i.v., or the racemate, as the free acid or sodium salt, p.o., in a cross-over design. The main kinetic parameters were calculated and formation and bioinversion curves plotted. The values of Cmax, Tmax and AUC were higher for the S(+) isomer. The percentage bioinversion averaged between 35-70% according to the form. This study proposes a new index for the calculation of bioinversion, independently of any i.v. administration, and confirms its self-limiting nature.

Stereoselective disposition and chiral inversion of KE-298, a new antirheumatic drug, in rats

The present study was an attempt to elucidate the relationship between stereoselective pharmacokinetics and protein binding of KE-298 and its active metabolites, deacetyl-KE-298 (M-1) and S-methyl-KE-298 (M-2). Metabolic chiral inversion was also investigated. The levels of unchanged KE-298 in plasma after oral administration of (+)-(S)-KE-298 to rats were lower than those of (-)-(R)-KE-298, whereas the levels of M-1 and M-2 after administration of (+)-(S)-KE-298 were higher than after (-)-(R)-KE-298. In vitro, rat plasma protein binding of (+)-(S)-KE-298 was lower than that of (-)-(R)-KE-298. In contrast, the binding of (+)-(S)-M-1 and (+)-(S)-M-2 was higher than that of (-)-(R)-M-1 and (-)-(R)-M-2. Displacement studies revealed that the (+)-(S) and (-)-(R)- enantiomers of KE-298 and their metabolites bound to the warfarin binding site on rat serum albumin. These results suggested that the stereoselective plasma levels in KE-298 and its metabolites were closely related to enantiomeric differences in protein binding attributed to quantitative differences in binding to albumin rather than to the different binding sites. Unidirectional chiral inversion was detected after oral administration of either (-)-(R)-KE-298 or (-)-(R)-M-2 to rats both yielding (+)-(S)-M-2.

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

The R enantiomers of some of the 2-arylpropionic acid non-steroidal antiinflammatory drugs (NSAIDs) are known to undergo metabolic chiral inversion to their more pharmacologically active antipodes. This process is drug and species dependent and usually unidirectional. The S to R chiral inversion, on the other hand, is rare and has been observed, in substantial extents, only for ibuprofen in guinea pigs and 2-phenylpropionic acid in dogs. After i.p. administration of single doses of racemic ketoprofen or its optically pure enantiomers to male CD-1 mice and subsequent study of the concentration time-course of the enantiomers, we noticed substantial chiral inversion in both directions. Following racemic doses, no stereoselectivity in the plasma-concentration time courses was observed. After dosing with optically pure enantiomer, the concentration of the administered enantiomer predominated during the absorption phase. During the terminal elimination phase, however, the enantiomers had the same concentrations. Our observation is suggestive of a rapid and reversible chiral inversion for ketoprofen enantiomers in mice.

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.

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.

HPLC determination of ketoprofen enantiomers in human serum using a nonporous octadecylsilane 1.5 microns column with hydroxypropyl beta-cyclodextrin as mobile phase additive

A sensitive and stereospecific high-performance liquid chromatography (HPLC) method for the quantitation of ketoprofen enantiomers in human serum was developed. The assay involves the use of an octadecylsilane solid-phase extraction for serum sample clean-up prior to HPLC analysis. Chromatographic resolution of the ketoprofen enantiomers was performed on a nonporous octyldecylsilane column with hydroxypropyl beta-cyclodextrin as the mobile phase additive. The composition of the mobile phase was 98:2 v/v aqueous 0.1% trifluoroacetic acid (TFA), pH 4.00 (adjusted with triethylamine (TEA))/acetonitrile containing 10 mM hydroxypropyl beta-cyclodextrin (beta-CD) at a flow rate of 0.8 ml min-1. Recoveries of R(-)-ketoprofen was 95.4 +/- 2.16% and for S(+)-ketoprofen 96.2 +/- 1.31%. Linear calibration curves were obtained in the range 0.025-15 micrograms ml-1 range for each enantiomer in serum. The detection limit based on a S/N = 3 ratio was 10 ng ml-1 for each enantiomer in serum with ultraviolet detection at 220 nm. The limit of quantitation for each enantiomer was 25 ng ml-1. Precision calculated as % relative standard deviation (%R.S.D.) and accuracy calculated as % error were in the range 0.2-5.2% and 0.3-2.2%, respectively, for the R enantiomer and 0.3-6.2 and 0.2-3.2%, respectively, for the S enantiomer.

Preclinical enantioselective pharmacology of (R)- and (S)- ketorolac

Many of the nonsteroidal anti-inflammatory drugs (NSAIDs) are marketed as racemic mixtures, composed of (R)- and (S)- enantiomers. Racemic NSAIDs are potent cyclooxygenase (COX) inhibitors only through the action of the (S)- enantiomers, as the (R)- enantiomers do not exhibit COX inhibition. However, the (R)- enantiomer of ketoprofen exhibits potent analgesic activity and minimal ulcerogenic potential. To extend these observations, we examined the (R)- and (S)- enantiomers of RS- ketorolac, (S)- ketorolac exhibited potent COX1 and COX2 enzyme inhibition, whereas (R)- ketorolac was > 100-fold less active on both COX subtypes. Both enantiomers did not affect norepinephrine or serotonin uptake sites, and nitric oxidase or lipoxygenase activities, nor did they demonstrate any affinity for opioid receptors (mu, delta, or kappa). In experimental models, (S)- ketorolac exhibited about 10-fold greater activity than (R)- ketorolac in the murine phenylquinone writhing model. In this model, morphine sulfate was effective at much lower doses, however, and neither (R)- nor (S)- ketorolac showed any morphine-sparing effect. In the rat gait test for analgesia in the foot paw after injection of brewers yeast suspension, neither (R)- nor (S)- ketorolac affected paw volume. However, both provoked changes in gait scores, the (S)- enantiomer being 30-fold more potent than the (R)- enantiomer. A similar reduction was observed with respect to ulcerogenic potential, measured by direct microscopic changes after test conclusion. These findings suggest that (R)- ketorolac may possess analgesic activity that is independent of COX inhibition and may be associated with reduced ulcerogenic potential compared to effects exhibited by (S)- ketorolac.

Methods of analysis of chiral non-steroidal anti-inflammatory drugs

Although the analysis of the enantiomers of chiral non-steroidal anti-inflammatory drugs (NSAIDs) has been carried out for over 20 years, there often remains a deficit within the pharmaceutical and medical sciences to address this issue. Hence, despite world-wide therapeutic use of chiral NSAIDs the importance of stereoselectivity in pharmacokinetic, pharmacodynamic and pharmacological activity and disposition has often been ignored. This review presents both the general principles that allow separation of chiral NSAID enantiomers, and discusses both the advantages and disadvantages of the available chromatographic assay methods and procedures used to separately quantify NSAID enantiomers in biological matrices.

Involvement of the rat gut epithelial and muscular layer, and microflora in chiral inversion and acyl-glucuronidation of R-fenoprofen

In the presence of excised human and rat gut, the pharmacologically inactive R enantiomers of both ibuprofen and fenoprofen (FN) are bioinverted to their anti-inflammatory antipodes. In an attempt to further localize the site of inversion, we incubated R-FN, in oxygenated (O2:CO2, 95:5, v/v) Krebs-Henseleit solution (37 degrees C, pH 7.4) for 3 h in the presence of the intestinal contents, epithelium and muscular layer of upper jejunum and everted jejunum sack of antibiotic treated (500 mg/kg neomycin and erythromycin b.i.d. for 3 days) and control adult female Sprague-Dawley rats. The formation of S-FN and acylglucuronidated FN was examined in the incubation medium using a stereospecific HPLC assay. The metabolic activities are reported per g of wet tissue. The extent of inversion by the everted rat gut was substantial (30.7 +/- 5.1%) but no significant differences between the control and germ-eradicated rats was observed. The epithelial cells were found to be the major site of inversion in the intestinal wall (37.5 +/- 4.7%) with the muscular layer (7.8 +/- 2.1%) and intestinal contents (5.7 +/- 2.2%) contributing only to a small extent to the process. Both enantiomers were substantially acyl-glucuconjugated in the epithelial and muscular layers, and the intestinal content.

Quantification of ketoprofen enantiomers in human plasma based on solid-phase extraction and enantioselective column chromatography

An HPLC method for the quantification of ketoprofen enantiomers in human plasma is described. Following extraction with a disposable C18 solid-phase extraction column, separation of ketoprofen enantiomers and I.S. (3,4-dimethoxy benzoic acid) was achieved using a chiral column [Chirex 3005; (R)-1-naphthylglycine 3,5-dinitrobenzoic acid] with the mobile phase, 0.02 M ammonium acetate in methanol, set at a flow-rate of 1.2 ml/min. Baseline separation of ketoprofen enantiomers and I.S., free from interferences, was achieved in less than 20 min. The calibration curves (n = 14) were linear over the concentration range of 0.16 to 5.00 micrograms/ml per enantiomer [mean r2 of 0.999 for both enantiomers, root mean square error were 0.015 for R(-) and 0.013 for S(+)]. The inter-day coefficient of variation for duplicate analysis of spiked samples was less than 7% and the accuracy was more than 93% over the over the concentration range of 0.2 to 4.0 micrograms/ml for individual enantiomer using 1 ml of plasma sample. This method has been applied to a pharmacokinetic study from healthy human volunteers following the administration of a ketoprofen extended release product (200 mg). This method is simple, fast and should find wide application in monitoring pharmacokinetic studies of ketoprofen.

Mechanistic studies on metabolic chiral inversion of 4-(4-methylphenyl)-2-methylthiomethyl-4-oxobutanoic acid (KE-748), an active metabolite of the new anti-rheumatic agent 2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (KE-298), in rats

The chiral inversion properties of 4-(4-methylphenyl)-2-methylthiomethyl-4-oxobutanoic acid (KE-748), an active metabolite of 2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanoic acid (KE-298), were compared with those of ibuprofen in rats. After administration of R(-)-[2 alpha-2H]KE-748, S(+)-KE-748 was present in the rat plasma, and the deuterium atoms of the S(+)-enantiomer were almost all replaced by hydrogen atoms. After administration of S(+)-[2 alpha-2H]KE-748, the deuterium content of S(+)-KE-748 in the plasma remained intact. In the in vitro study, using a cell-free system and rat liver homogenates, the chiral inversion of ibuprofen was apparent when both CoA and ATP were present; however, KE-748 was not inverted. In the study on isolated rat hepatocytes, the unidirectional chiral inversion from R(-)-to S(+)-enantiomer was observed for both ibuprofen and KE-748. When R(-)-ibuprofen was incubated with medium and long chain fatty acids (carbon chain length C6 to C16), using isolated hepatocytes, the chiral inversion decreased significantly. On the other hand, when R(-)-KE-748 was incubated with short and medium chain fatty acids (carbon chain length C3 to C8), chiral inversion was inhibited markedly. To induce hepatic microsomal long chain fatty acid CoA ligase, rats were treated with clofibric acid (CF rats). In both in vitro and in vivo experiments on CF rats, chiral inversion from R(-)-to S(+)-ibuprofen was enhanced significantly compared with that in controls, whereas the enhancement was not observed in the case of R(-)-KE-748. There was no influence of benzoic acid, a typical substrate on medium chain fatty acid CoA ligase in the mitochondrial matrix, on chiral inversion of R(-)-ibuprofen, using, isolated hepatocytes. In contrast, the chiral inversion from R(-)-to S(+)-KE-748 was strongly inhibited in the presence of benzoic acid. These results indicate that chiral inversion of R(-)-KE-748 may proceed via formation of the CoA-thioester intermediate with loss of the 2 alpha-methine proton, in a manner similar to that seem with R(-)-ibuprofen. However, the enzymes needed to form CoA-thioester of R(-)-KE-748 differ from those for R(-)-ibuprofen.

Pharmacokinetics and pharmacodynamics of ketoprofen enantiomers in the horse

Pharmacokinetic and pharmacodynamic parameters were established for enantiomers of the non-steroidal anti-inflammatory drug (NSAID) ketoprofen (KTP), each administered separately at a dose level of 1.1 mg/kg to a group of six New Forest geldings, in a three-period cross-over study using a tissue cage model of inflammation. For both S(+)-and R(-)-KTP, penetration into tissue cage fluid (transudate) and inflamed tissue cage fluid (exudate) was rapid, and clearances from exudate and transudate were much slower than from plasma. AUC values were, therefore, higher for exudate and, to a lesser degree, transudate than for plasma. Unidirectional chiral inversion of R(-)-to S(+)-KTP was demonstrated. Administration of both enantiomers produced marked, time-dependent inhibition of synthesis of serum thromboxane B2 and exudate prostaglandin E2, indicating non-selective inhibition of cyclo-oxygenase (COX) isoenzymes COX-1 and COX-2 respectively. Administration of both enantiomers also produced partial inhibition of beta-glucuronidase release into inflammatory exudate and of bradykinin-induced skin oedema. It is suggested that, although S(+)-KTP is generally regarded as the eutomer, R(-)-KTP was probably at least as active in inhibiting bradykinin swelling. Pharmacokinetic/pharmacodynamic (PK/PD) modelling of the data could not be undertaken following R(-)-KTP administration because of chiral inversion to S(+)-KTP, but pharmacodynamic parameters, Emax, EC50, N, keO and t1/2(keO). were determined for s(+)-KTP using the sigmoidal Emax equation. PK/DP modelling provided a novel means of comparing and quantifying several biological effects of KTP and of investigating its mechanisms of action.

Chiral kinetics and dynamics of ketorolac

It has been shown that the analgesic and cyclooxygenase inhibitor activity of ketorolac tromethamine (KT), which is marketed as the racemic mixture of (-)S and (+)R enantiomers, resides primarily with (-)S ketorolac and that the ulcerogenic activity of this agent also resides in (-)S ketorolac. Resolution of individual enantiomers for analysis in plasma samples has been accomplished by two methods: derivatization to form diastereomers that are separated by HPLC, or direct HPLC using a chiral phase column. When mice and rats were given oral solutions of (-)S and (+) KT, it was found that the kinetics and interconversion of the enantiomers were species and dose dependent. Interconversion was higher in mice than in rats; when (-)S KT was administered, 71% of the area under the concentration-time curve (AUC) was due to (+)R ketorolac in mice, compared with 12% in rats. More interconversion was observed at higher doses; the percent of AUC due to (-)S ketorolac when (+)R KT was administered increased from 12% to 25% in mice and from 2% to 8% in rats. In general, more interconversion occurred from (-)S to (+)R ketorolac in the animal studies. Human subjects were given single oral solution doses of racemic KT (30 mg), (-)S KT (15 mg), and (+)R KT (15 mg). The plasma concentrations of (-)S ketorolac were lower than (+)R ketorolac at all sample times after racemic KT (22% of the AUC was due to (-)S ketorolac). When (+)R KT was administered, (-)S ketorolac was not detectable and interconversion was essentially 0%. When (-)S KT was administered, significant levels of (+)R ketorolac were detectable and interconversion was 6.5%. After all doses, plasma half-life was shorter and clearance greater for (-)S ketorolac than for (+)R ketorolac. Thus, in humans very little or no interconversion of (+)R to (-)S was observed, and interconversion of (-)S to (+)R was minimal (6.5%). These data demonstrate that the kinetics and interconversion of the enantiomers of ketorolac is different in animals and humans as well as from most other NSAIDs. This may be due to more rapid excretion or metabolism of (-)S ketorolac and a different mechanism of interconversion.

Moment analysis of stereoselective enterohepatic circulation and unidirectional chiral inversion of ketoprofen enantiomers in rat

The stereoselective enterohepatic circulation (EHC) and the synchronous chiral inversion of ketoprofen enantiomer in rat were evaluated by moment analysis based on the recirculatory concept. (R)-(-)- and (S)-(+)-ketoprofen were independently administered into rats, and the plasma and bile concentrations of both enantiomers were determined by a column-switching HPLC. (S)-Ketoprofen was generated by the chiral inversion from (R)-ketoprofen, whereas (R)-ketoprofen was not generated from (S)-ketoprofen. Within 30 min after intravenous administrations, the plasma time courses of R- and S-enantiomers were almost the same between rats with laparotomy and those with bile-duct cannula. After 30 min, the plasma concentrations in rats with laparotomy were significantly higher than those in rats with bile-duct cannula. The Laplace-transformed equations for stereoselective EHC and the synchronous chiral inversion were derived by means of the transfer function method on the basis of the recirculatory theory. The global moments (AUC and MRT) which were derived directly from the transformed equations were related to the local moments for the single EHC. The recirculation ratios of (R)- and (S)-ketoprofen for the single EHC were estimated to be 15.4% and 63.6%, respectively. The absorption ratios of (R)- and (S)-ketoprofen for the absorption process from the gastrointestinal tract into the systemic circulation were 87.0% and 83.8%, respectively. The biliary excretion rations of (R)- and (S)-ketoprofen for the disposition process through the systemic circulation into the bile were 17.7% and 75.8%, respectively. The chiral inversion ratio from (R)-ketoprofen into (S)-ketoprofen was 59.5%. The complicated disposition of ketoprofen, i.e., the simultaneous EHC and chiral inversion, was able to be analyzed by a moment method in a simple way.

New insights into the site and mode of antinociceptive action of flurbiprofen enantiomers

The S-enantiomer of flurbiprofen has been shown to have both antiinflammatory and antinociceptive effects, whereas R-flurbiprofen is antinociceptive but not antiinflammatory. Importantly, only S-flurbiprofen inhibited prostaglandin biosynthesis in vitro at therapeutic concentrations. R-flurbiprofen did not undergo significant chiral inversion to S-flurbiprofen in rats and humans. A study was conducted to gain new insight into the possible sites and modes of action of flurbiprofen enantiomers. In a modified Randall Selitto assay, both enantiomers were antinociceptive in a dose-dependent manner after systemic administration. After local administration into the inflamed paw, only S-flurbiprofen produced significant dose-related antinociception. In a physiologic study, we recorded extracellularly from nociceptive spinal cord neurons that were rendered hyperexcitable. Intravenous administration of R- and S-flurbiprofen reduced responses of neurons to pressure applied to the inflamed knee and the noninflamed ankle and paw in a dose-dependent manner. When injected directly into the knee joint, only S-flurbiprofen but not R-flurbiprofen reduced responses to pressure. These results suggest a central site of antinociceptive action for R- and S-flurbiprofen and an additional peripheral site for S-flurbiprofen. The findings may be of clinical relevance, as it was demonstrated that both enantiomers also were antinociceptive in humans. Because R-flurbiprofen caused less toxicity in rats than the S-enantiomer or the racemic compound, a reduction in the quantitatively most important side effects in the gastrointestinal tract might be achieved with the use of R-flurbiprofen for pain therapy.

Stereospecific determination of tiaprofenic acid in plasma: problems with drug degradation

A sensitive stereospecific high-performance liquid chromatographic assay for the quantification of tiaprofenic acid in human plasma was developed. The procedure involved extraction of tiaprofenic acid from acidified plasma into hexanediethyl ether (8:2, v/v). Stereospecific separation was achieved with a prepacked alpha1-acid glycoprotein column without derivatization. The mobile phase consisted of 2% 2-propanol in 0.01 M phosphate buffer, pH 6.5. Tiaprofenic acid was detected at 317 nm. The limit of quantification was found to be 25 ng/ml for each enantiomer using a 0.5 ml plasma sample. The assay was reproducible and accurate to be applied to the stereoselective pharmacokinetic analysis of tiaprofenic acid in plasma. Because of photoinstability of tiaprofenic acid plasma sampling and sample extraction should be performed under light protection.

Preclinical and clinical development 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 pharmacokinetic profile of ketoprofen and its enantiomers was assessed in several animals species and in human volunteers. In humans, the relative bioavailability of oral dexketoprofen trometamol (12.5 and 25 mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50 mg, 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. Peak plasma concentrations of 1.4 and 3.1 mg/L are reached after administration of dexketoprofen trometamol 12.5 and 25 mg, respectively. From 70 to 80% of the administered dose is recovered in the urine during the first 12 hours, mainly as the acyl-glucuronoconjugated parent drug. No R(-)-ketoprofen is found in the urine after administration of dexketoprofen [S(+)-ketoprofen], confirming the absence of bioinversion of the S(+)-enantiomer in humans. in animal studies, the anti-inflammatory potency of dexketoprofen was always equivalent to that demonstrated by twice the dose of ketoprofen. Similarly, animal studies showed a high analgesic potency for dexketoprofen trometamol. The R(-)-enantiomer demonstrated a much lower potency, its analgesic action being apparent only in conditions where the metabolic bioinversion to the S(+)-enantiomer was significant. The gastric ulcerogenic effect of dexketoprofen at various oral doses (1.5 to 6 mg/kg) in the rat do not differ from those of the corresponding double doses (3 to 12 mg/kg) of racemic ketoprofen. Repeated (5-day) oral administration of dexketoprofen as the trometamol salt causes less gastric ulceration than was observed after the acid form of both dexketoprofen and the racemate. In addition, single dose dexketoprofen as the free acid at 10 to 20 mg/kg does not show a significant intestinal ulcerogenic effect in rats, while racemic ketoprofen 20 or 40 mg/kg is clearly ulcerogenic to the small intestine. The analgesic efficacy of oral dexketoprofen trometamol 10 to 20 mg is superior to that of placebo and similar to that of ibuprofen 400 mg in patients with moderate to serve pain after third molar extraction. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol than in those treated with ibuprofen 400 mg. Dexketoprofen trometamol was well tolerated, with a reported incidence of adverse events similar to that of placebo.

Moment analysis of stereoselective biliary excretion and chiral inversion of ketoprofen enantiomers in perfused rat liver

The stereoselective local disposition of ketoprofen was evaluated by the single-pass perfusion experiment following a bolus injection of R(-)- or S(+)-ketoprofen into the liver from the portal vein. The elution time profiles of enantiomers into the hepatic vein and the excretion time profiles into the bile were kinetically assessed by local moment analysis. The hepatic recovery ratios (FH) of both enantiomers were < 1%, and the mean hepatic transit times (tH) were approximately 7 s. After the injection of S-ketoprofen into the liver, the biliary excretion ratio (Fb) of total S-ketoprofen was 68% (15% S-ketoprofen and 53% glucuronide) and the mean biliary transit time (tb) of S-ketoprofen was 10 min. R-Ketoprofen inversion from S-ketoprofen was not observed in either the perfusate or in the bile. After the injection of R-ketoprofen, the Fb of total R-ketoprofen was 12% (3% R-ketoprofen and 9% glucuronide), and tb of R-ketoprofen was 8 min. The Fb of total S-ketoprofen inverted from R-ketoprofen was 24% (7% S-ketoprofen and 17% glucuronide), and the tb of inverted S-ketoprofen was 17 min. Forty-six percent of R-ketoprofen was inverted to S-ketoprofen during a single pass through the rat liver, and the mean inversion time was 7.5 min. It was concluded that the unidirectional chiral inversion of ketoprofen was stereospecific, and the hepatic uptake and biliary excretion were stereo-nonspecific.

Stereochemical aspects of pharmacotherapy

Over the past 15 years stereoselectivity has become a well-recognized consideration in clinical pharmacology. Drugs that have an asymmetric center or plane of symmetry within their molecular structure are said to be chiral. They are available as pairs of nonsuperimposable mirror images, called enantiomers, that share essentially the same physicochemical properties. These three-dimensional structural differences, however, can translate into enantiospecific pharmacologic or pharmacokinetic properties, which may be important in understanding the clinical pharmacology of chiral drugs. Most chiral drugs are available as the racemate, in which equal proportions of the two enantiomers are administered concurrently. The pharmacologic and disposition properties of many chiral drugs are documented to be stereospecific, and this has influenced the regulatory requirements for the approval of new drug candidates. Due to this influence on new drug development, the possible issues surrounding racemic drugs will undoubtedly affect the types of pharmaceuticals that are used clinically in the next century. Accordingly, considerable advances have been made in producing optically pure drug. It should be emphasized, however, that stereochemically pure drugs are not necessarily superior to the respective racemates.

Dose-dependency of flurbiprofen enantiomer pharmacokinetics in the rat

Flurbiprofen is a chiral 2-arylpropionate used clinically as a racemate. Previously a significant pharmacokinetic interaction between the enantiomers of flurbiprofen has been reported in both rats and humans. The possible mechanism for this interaction was believed to involve competitive protein binding between the enantiomers. In addition, the saturable binding of flurbiprofen enantiomers in vitro in human plasma has been demonstrated. In this study different doses of racemic flurbiprofen were administered to rats to create differing extents of competition for protein binding sites between the enantiomers. There was a statistically significant dose-dependent increase in total body clearance and volume of distribution of both the R and S enantiomers. However, there was no change in either the S/R AUC ratio or the elimination rate constants for (R)- or (S)-flurbiprofen with increasing dose. These results are consistent with the hypothesis that the increasing amount of (R)- and (S)-flurbiprofen in the body causes displacement of flurbiprofen enantiomers from their protein binding sites, resulting in their increased total body clearance and volume of distribution. Further, the data suggest that previously reported extents of R to S enantiomeric inversion for other 2-arylpropionates may not be accurate if the enantiomers exhibit nonlinear kinetics or there is a significant kinetic interaction between the enantiomers.

Enantiospecific analysis: applications in bioanalysis and metabolism

Enantiospecific analysis has a significant role in modern drug development from discovery-chemistry to the clinical evaluation of novel compounds. Chromatographic techniques, involving the use of either chiral derivatizing agents or chiral stationary phases, represent the most commonly used approaches to enantiospecific analysis. The advantages and limitations of these two techniques are examined using the analysis of the enantiomers of the 2-arylpropionic acids (tiaprofenic acid and ibuprofen) and the chiral N-oxides of N-ethyl-N-methylaniline and pargyline, as representative examples for each approach. The potential of biosensors in enantiospecific analysis is addressed and some preliminary results on the development of an enantioselective biosensor for the analysis of (S)-warfarin are presented.

Etodolac clinical pharmacokinetics

Etodolac is a chiral nonsteroidal anti-inflammatory drug (NSAID) that is marked as the racemate. Currently, the drug is available in several countries for the treatment of arthritis and the alleviation of pain. Etodolac possesses several unique disposition features mainly due to its stereoselective pharmacokinetics. In plasma, the concentrations of the 'inactive' R-enantiomer are about 10-fold higher than those of the active S-enantiomer, an observation that is novel among the chiral NSAIDs. In common with other NSAIDs, the drug is highly plasma protein bound, and undergoes virtually complete biotransformation to oxidised metabolites and acyl-glucuronides. Etodolac is well absorbed, with maximal plasma concentrations attained within 1 to 2 hours in healthy volunteers. The area under the plasma concentration-time curve of racemic etodolac increases linearly with doses used clinically. The elimination half-life of etodolac is between 6 and 8 hours in plasma, and is similar for both enantiomers. The volume of distribution (Vd) of racemic etodolac is higher than that of most other NSAIDs mainly because of the extensive distribution of the S-enantiomer. The very large Vd of the S-enantiomer, compared with its antipode is, at least in part, due to its less extensive plasma protein binding. In addition to the unchanged drug, substantial concentrations of the acyl-glucuronides of etodolac are found in both plasma and the synovial fluid of patients with arthritis. A limited amount of conjugated etodolac is found in the bile of patients following cholecystectomy. Hepatic cirrhosis has no effect on the pharmacokinetics of racemic etodolac, although the effect of hepatic dysfunction on the pharmacokinetics of the individual enantiomers has yet to be determined. In elderly non-arthritic individuals with excellent kidney function, aging does not affect the pharmacokinetics of etodolac. The pharmacokinetics of the drug in patients with renal failure have not been published, and may be important because the acyl-glucuronides are renally cleared.

Evidence of absorption rate dependency of ibuprofen inversion in the rat

Ibuprofen (IB) is a chiral 2-arylpropionic acid derivative used as a nonsteroidal antiinflammatory drug (NSAID). It undergoes substantial R to S chiral inversion in humans and rats. In addition to systemic inversion, presystemic chiral inversion has been suggested for IB in humans but only after administration of formulations with slow absorption rates. In search for a suitable animal model, the absorption rate dependency of the extent of inversion was examined in male Sprague-Dawley rats given 20 mg/kg of racemic IB in aqueous solution (Tmax, 0.6 h), suspension (Tmax, 1 h) or as sustained release granules (Tmax, 2.3 h). In addition, (R)-IB (5 mg/liter) was incubated in the presence of everted rat gut segments in an organ bath at 37 degrees. After sustained release granules, the S:R AUC ratios (7.3 +/- 1.5) were significantly higher than suspension (3.6 +/- 1.1) and solution (3.5 +/- 0.2). Accordingly, AUCS and AUCR, as percent of the total AUC (S+R), significantly increased and decreased, respectively, after administration of the sustained released granules as compared with the solution and suspension. A significant positive linear correlation was found between the S:R AUC ratios and the corresponding Tmax for (R)-IB (r = 0.82). In vitro, (R)-IB was inverted by everted jejunum (12.2 +/- 1.6%), ileum (14.2 +/- 2.0%), and colon (4.4 +/- 0.6%) segments. IB was also glucuronidated in the presence of the intestinal segments. Therefore, similar to earlier observations made in humans, in the rat, the S:R AUC ratio was positively and significantly correlated with the absorption rate from the dosage form.(ABSTRACT TRUNCATED AT 250 WORDS)