Separation of four isomeric tropane alkaloids from Schizanthus grahamii by non-aqueous capillary electrophoresis

The potential of non-aqueous capillary electrophoresis was investigated for the separation of four isomeric tropane alkaloids, namely 3alpha-senecioyloxy-7beta-hydroxytropane, 3alpha-hydroxy-7beta-senecioyloxytropane, 3alpha-hydroxy-7beta-angeloyloxytropane and 3alpha-hydroxy-7beta-tigloyloxytropane extracted from Schizanthus grahamii. The composition of the organic solvent and the nature of the electrolyte were of considerable importance with respect to selectivity. Different organic solvents (i.e. methanol, ethanol, acetonitrile, tetrahydrofuran) and mixtures thereof were investigated. Moreover, different electrolytes such as formate, acetate and trifluoroacetate were tested. After optimisation, an electrolyte consisting of 1 M trifluoroacetic acid and 25 mM ammonium trifluoroacetate in methanol:ethanol (40:60, v:v) was selected. It provided an efficient separation of the four positional isomers as well as a good repeatability of migration time (RSD < 0.2%). The method was successfully used with electrospray MS to confirm the molecular mass of the tropane alkaloids.

Development of a bioreactor based on trypsin immobilized on monolithic support for the on-line digestion and identification of proteins

The preparation and characterization of a new trypsin-based bioreactor is here described for on-line protein digestion and peptide analysis. Trypsin was immobilized on an epoxy-modified silica monolithic support with a single reaction step and the amount of immobilized enzyme was found to be 66.07 mg (+/-11.75 S.D.)/column (n = 6). The bioreactor was coupled through a switching valve to an analytical column for the on-line digestion, peptide separation and identification of test proteins by ESI-MS-MS. The influence of various parameters (flow rate, temperature, buffer pH and molarity, etc.) on enzymatic activity was investigated by an experimental design and the mostly significant factor was found to be the flow rate. The efficacy of the reported on-line bioreactor for tryptic mapping is reported for somatostatin and myoglobin, selected as model compounds. Tryptic peptide maps obtained by on-line digestion of myoglobin were compared to those obtained by traditional off-line digestion. Sequence coverage obtained with the on-line protocol (21 peptides, 75.16% coverage of myoglobin sequence) was found to be comparable to the one obtained with the off-line protocol (18 peptides, 76.47% coverage). Sensitivity for myoglobin digestion and identification was 0.1 mg/ml. The reproducibily of the peptide maps in terms of retention time was from 1.53 to 4.31%, R.S.D.

Use of large particles support for fast analysis of methadone and its primary metabolite in human plasma by liquid chromatography-mass spectrometry

A bioanalytical method was developed for the quantitation of methadone (MTD) and its primary metabolite, (EDDP) in plasma. The extraction step was performed within a capillary column packed with large particles (35x0.3 mm I.D.; d(p) 30 micrometer) at high flow-rate conditions (450 microliter/min). The separation was performed on a microbore analytical column (55x2 mm I.D.; d(p) 3 micrometer) coupled to a mass spectrometer (MS). This procedure was based on a column-switching unit. Analytes of interest were retained on the precolumn by hydrophobic interactions and backflushed from the precolumn to the analytical column. The detection was carried out with a MS single quadrupole equipped with an electrospray interface. The total analysis time was 6 min. The limits of quantification were evaluated at 10 and 25 ng/ml for MTD and EDDP, respectively. At this level, good accuracies were obtained for both analytes with repeatability values less than 18%.

Focused microwave-assisted extraction of cocaine and benzoylecgonine from coca leaves

Extraction of cocaine and benzoylecgonine from coca leaves was performed by focused microwave-assisted extraction (FMAE). Cocaine extraction was optimised with respect to the nature of the extracting solvent, the particle size distribution, the moisture of the sample, the applied microwave power and the radiation time. A central composite design was used to optimise the two latter parameters and to assess the robustness of the extraction method around the best conditions. FMAE generated extracts similar to those obtained by conventional solid-liquid extraction but in a more efficient manner, i.e. 30 s were sufficient to extract cocaine quantitatively from leaves. Analyses of cocaine and benzoylecgonine in coca leaves was carried out by capillary GC-FID and GC-MS for peak identification, as well as by capillary electrophoresis with UV detection.

New trends in extraction, identification and quantification of artemisinin and its derivatives

Artemisinin, a sesquiterpene lactone endoperoxide, and a number of its precursors, metabolites and semisynthetic derivatives have shown to possess antimalarial properties. Several methods have been reported for the measurement of artemisinin and its main derivatives in plant material and biological fluids. However, most of them are either not sufficiently sensitive and do not offer reliable results, or are difficult to apply in routine analyses. Therefore, new methods for the determination of these compounds, such as supercritical fluid extraction and chromatography, pressurized solvent extraction, microwave-assisted extraction, high-performance liquid chromatography coupled to mass spectrometry or evaporative light scattering detection, will be presented. Applications to plant material, pharmaceutical formulations and biological fluids will also be reviewed.

Calystegine distribution in some solanaceous species

The distribution of eight calystegines (A(3), A(5), B(1), B(2), B(3), B(4), C(1) and N(1)) and their content was investigated by gas chromatography coupled to mass spectrometry (GC-MS) in Datura metel, Atropa belladonna, Hyoscyamus albus, Mandragora autumnalis, Solanum sodomaeum, Withania somnifera, Withania frutescens and Brunfelsia nitida. The most frequently encountered calystegines were A(3), B(1), B(2) and B(3), while distribution of N(1) and C(1) was more limited. In all the investigated samples, calystegines A(5) and B(4) were never detected. This report focuses for the first time on calystegines in Withania and Brunfelsia genera and in Mandragora autumnalis and Solanum sodomaeum species.

Routine o-glycan characterization in nutritional supplements--a comparison of analytical methods for the monitoring of the bovine kappa-casein macropeptide glycosylation

Analytical procedures, including capillary isoelectric focusing (CIEF), high-performance anion-exchange chromatography coupled to amperometric detection (HPAEC-PAD) and normal-phase chromatography with fluorescence detection are presented for the characterization of a highly O-glycosylated caseinomacropeptide (CGMP) and the detection of subtle glycosylation differences between CGMP Batches obtained with two different preparation procedures. Modified two-step CIEF allowed monitoring of glycopeptide heterogeneity and determination of the isoelectric points of acidic glycoforms. The mixture of wide and narrow pH range ampholytes was optimized to improve glycoform resolution. The pI of the different CGMP glycoforms was evaluated with pI internal standards and found to range between 3.08 and 3.58, which indicates a very acidic glycopeptide. Moreover, the monosaccharide composition was determined with HPAEC-PAD after neutral and amino sugars release by using adequate acidic hydrolysis of CGMP. Results indicated a similar composition for Batches I and II, but the monosaccharide percentages were 3-4 fold higher in Batch I, particularly for galactose and glucose. This likely reflects a higher content in lactose in the case of Batch I. Finally, O-linked oligosaccharides were released with an automated hydrazinolysis and derivatized with a sensitive labelling reagent, 2-aminobenzamide. The derivatives were then analyzed by normal-phase HPLC coupled with fluorescence detection, and separated on the basis of hydrophilic interaction, which allowed oligosaccharide mapping of the two CGMP. It appeared that the two CGMP preparations had an almost identical O-glycan population, but CGMP Batch I was more glycosylated than Batch II. Additionally, the sizes of the separated glycans, expressed as the number of glucose units, were tentatively assigned using calibration with a partial hydrolysate of dextran. In conclusion, a combination of electrophoretic and chromatographic techniques was found powerful in studying glycoprotein heterogeneity and assessing batch-to-batch consistency.

On-line capillary electrophoresis-electrospray mass spectrometry for the stereoselective analysis of drugs and metabolites

The on-line combination of partial-filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the enantioseparation of pharmaceutical drugs and metabolites, namely amphetamines, methadone, venlafaxine and selected tropane alkaloids. The partial-filling technique proved to be a suitable and efficient approach to avoid mass spectrometry (MS) source contamination, as well as signal suppression due to nonvolatile additives. To achieve chiral separation, various chiral selectors were applied, including neutral and particularly negatively charged cyclodextrins. Because of the countercurrent contribution, charged cyclodextrins were found more suitable for the on-line MS detection of separated enantiomers. Hyphenation of capillary electrophoresis (CE) with mass spectrometry was found appropriate for the stereoselective analysis of methadone in real serum samples. Moreover, the use of MS in the selected ion monitoring mode resulted in a very high selectivity, as well as improved sensitivity compared to UV detection. Finally, with atropine as a model compound, the quantitative performances of the method were evaluated and showed high sensitivity, as well as good repeatability in terms of migration time and peak area ratio.

Experimental designs to investigate capillary electrophoresis-electrospray ionization-mass spectrometry enantioseparation with the partial-filling technique

An experimental design approach is described to evaluate the main electrophoretic parameters involved in the enantioseparation of pharmaceuticals by capillary electrophoresis (CE) coupled to electrospray ionization-mass spectrometry (ESI-MS). For all experiments, the partial-filling technique was applied to avoid the chiral selector entering in the mass spectrometer ion source with a negative effect on the electrospray performance. To carry out enantioseparation, a volatile buffer constituted of 20 mM ammonium acetate at pH 4.0, and a polyvinyl alcohol-coated capillary were used. Methadone was employed as the model compound and three different cyclodextrins (CDs), namely sulfobutyl ether-beta-CD, carboxymethylated-beta-CD and hydroxypropyl-beta-CD, were selected in order to study the countercurrent process. Two different experimental designs were chosen: (i) a full-factorial design to examine the effects and significance of the investigated factors, and (ii) a central composite face-centered design to establish the mathematical model of the selected responses in function of experimental factors. The chiral selector concentration, percentage of the capillary filled with the chiral selector, and drying gas nebulization pressure were three relevant factors taken into consideration. For each CD, the methadone enantiomeric resolution, apparent selectivity, and migration time of the second enantiomer were established as responses. The latter were systematically related to experimental parameters with the help of multiple linear regression. It is noteworthy that the behaviour was different in function of the chiral selector charge. Results revealed that the nebulization pressure involved in the electrospray process and the CD concentration had a significant effect on the enantiomeric resolution, while the effect of the separation zone length was less pronounced. Finally, response surfaces were drawn from the mathematical model and experimental conditions were selected to allow a robust determination of methadone enantiomers by CE-MS.

Parameters affecting microwave-assisted extraction of withanolides

Focused microwave-assisted extraction was applied to the extraction of three main withanolides from airdried leaves of Iochroma gesnerioides, namely, withaferin A, iochromolide and withacnistin. Six extraction variables, i.e. nature and volume of extracting solvent, sample moisture, extraction time, power of irradiation and particle size, were investigated with respect to the recovery of withanolides. The most favourable conditions were obtained by using powdered plant material (< 220 microns), previously impregnated with water for 15 min, and extracted with methanol for 40 s at 25 W. The results obtained using the optimised method were compared to those achievable with Soxhlet extraction.

Non-aqueous capillary electrophoresis with diode array and electrospray mass spectrometric detection for the analysis of selected steroidal alkaloids in plant extracts

Nonaqueous capillary electrophoresis coupled to UV detection is described for the separation and determination of steroidal alkaloids. After optimization of electrophoretic parameters, including the electrolyte nature and the organic solvent composition, a reliable separation of solasodine and solanidine was achieved in a methanol-acetonitrile (20:80, v/v) mixture containing 25 mM ammonium acetate and 1 M acetic acid. For quantitative purposes, a fused-silica capillary with a bubble cell was used and detection was performed at low wavelength (195 nm). Method performances, including migration time and peak area reproducibility, linearity, sensitivity and accuracy, were also evaluated. The method was applied to determine solasodine in Solanum elaeagnifolium berries and Solanum sodomaeum leaves and seeds. To further improve sensitivity in the analysis of solasodine-related compounds, solanidine, demissidine and tomatidine, the developed method was interfaced with electrospray ionization mass spectrometry. In the case of solasodine, the detection limit was estimated at 3 microg/ml for NACE-UV and at 0.05 microg/ml for NACE-MS, in the selected ion-monitoring mode.

HPLC-UV and HPLC-positive-ESI-MS analysis of the diterpenoid fraction from caper spurge (Euphorbia lathyris) seed oil

Caper spurge (Euphorbia lathyris L.) seed oil contains a series of diterpenoids known as Euphorbia factors, or L-factors, L1-L9. They are esters of several polyols (lathyrol, epoxylathyrol, hydroxylathyrol and ingenol) and account for about 3-5% of the oil. The percentage of ingenol-based L-factors is very low, less than 5% of the diterpenoid fraction, but some of them (factors L5 and L6) are responsible for the irritant and co-carcinogenic activities of the oil. This paper reports an HPLC-UV and HPLC-positive-ESI-MS analysis of the diterpenoid fraction of caper spurge seed oil before and after selective hydrolysis of ingenol-based L-factors. Separation of lathyrane polyols and esters, and ingenol and its esters was achieved using a chromatographic system consisting of a C18 stationary phase and acetonitrile: water as mobile phase. A new macrocyclic constituent, the deoxy Euphorbia factor L1, was identified in the oil.

Use of vancomycin silica stationary phase in packed capillary electrochromatography. II. Enantiomer separation of venlafaxine and O-desmethylvenlafaxine in human plasma

A capillary electrochromatography method, using vancomycin chiral stationary phase packed capillary, was optimized for the simultaneous chiral separation of the antidepressant drug venlafaxine and its main active metabolite O-desmethylvenlafaxine. Simultaneous baseline enantiomeric separation of the two compounds was obtained using a mobile phase composed of 100 mM ammonium acetate buffer pH 6/water/acetonitrile (5:5:90, v/v). The electrokinetic injection for sample introduction provided a limit of quantitation for both the compounds of 0.05 microg/ml racemate concentration suitable for the analysis of venlafaxine and metabolite in biological samples. The acetonitrile mobile phase concentration was found to modulate the analytes elution times, the enantiomeric resolution and the efficiency of the separation. The column was tested for repeatability and linearity showing RSD values (%) in the range of 0.13-0.24, 2.47-3.66 and 1.35-2.50 for migration time, sample/internal standard peak area ratio and enantiomeric resolution, respectively and correlation coefficients higher than 0.9990. The method was applied to the analysis of clinical samples of patients under depression therapy showing a stereoselective metabolism for venlafaxine.

Capillary electrophoresis and high-performance anion exchange chromatography for monitoring caseinoglycomacropeptide sialylation

Capillary zone electrophoresis was applied to separate caseinoglycomacropeptide glycoforms and characterize microheterogeneity of the glycopeptide. Particular attention was paid to the sialic acid content in caseinoglycomacropeptide obtained through different manufacturing processes. A chemometric approach was used to simultaneously study effects of acid concentration, hydrolysis time and temperature on sialic acid release from caseinoglycomacropeptide. Hydrolysis conditions that maximize sialic acid release were chosen. Sialic acid was determined using high performance anion exchange chromatography coupled with pulsed amperometric detection. Results were compared to those obtained by alternative techniques, such as colorimetric and enzymatic methods.

Nonaqueous capillary electrophoresis-mass spectrometry for separation of venlafaxine and its phase I metabolites

Aqueous and nonaqueous capillary electrophoresis (NACE) were investigated for separation of venlafaxine, a new second-generation antidepressant, and its three phase I metabolites. Working at basic pH, around the venlafaxine pKa value, was effective in resolving the investigated drugs, but created considerable peak tailing. To overcome electrostatic interactions between analytes and silanol groups, investigations were also carried out at acidic pH. However, despite the addition of up to 50% v/v of organic solvents (e.g., methanol or acetonitrile), complete separation of the studied compounds was not possible. NACE was found to be an appropriate alternative to resolve venlafaxine and its metabolites simultaneously. Using a conventional capillary (fused-silica, 64.5 cm length, 50 microm inner diameter), and a methanol-acetonitrile mixture (20/80 v/v) containing 25 mM ammonium formate and 1 M formic acid, complete resolution of these closely related compounds was performed in less than 3.5 min. Selectivity, efficiency and separation time were greatly affected by the organic solvent composition. As the electric current generated in nonaqueous medium was very low, the electric field was further increased by reducing the capillary length. This allowed a baseline resolution of venlafaxine and its three metabolities in 0.7 min. Selectivity was compared in aqueous and nonaqueous media in relation to the acid-base properties of the analytes as well as to the solvation degree. Finally, the method successfully coupled on-line to mass spectrometry with electrospray ionization interface allowed significant sensitivity enhancement.

Use of borate complexation for the separation of non-UV-absorbing calystegines by capillary electrophoresis

A capillary zone electrophoresis method was developed for the simultaneous analysis of seven closely related polyhydroxyalkaloids called calystegines. Successful results were obtained with a fused-silica capillary, 80 mM sodium tetraborate at pH 9.2 and temperature of 50 degrees C. Detection of non-UV-absorbing calystegines was achieved through in-situ complexation with borate ions. To further improve method sensitivity, a capillary with a bubble cell was used and detection performed at low wavelength (191 nm). Effects of buffer concentration, pH and temperature on migration times and efficiency are discussed. Migration behavior of selected compounds was significantly affected by their chemical structure (i.e., number and position of hydroxy groups). Under optimized conditions, baseline separation of the selected compounds was achieved in less than 12 min. Precision was evaluated by measuring repeatability and intermediate precision of migration times and corrected peak areas. Finally, the method was applied to the qualitative analysis of calystegines in plant extracts and results were confirmed by GC-MS.

Simultaneous analysis of some amphetamine derivatives in urine by nonaqueous capillary electrophoresis coupled to electrospray ionization mass spectrometry

A nonaqueous capillary electrophoresis method, coupled to UV and electrospray mass spectrometry (ESI-MS), is described for the simultaneous analysis of Ecstasy and other related derivatives. Several electrophoretic and ESI-MS parameters were systematically investigated, such as electrolyte nature and concentration, organic solvent and sheath liquid compositions, nebulization gas pressure and drying gas flow-rate. The best results were achieved with an acetonitrile-methanol (80:20, v/v) mixture containing 25 mM ammonium formate and 1 M formic acid, an applied voltage of 30 kV and a separation temperature of 15 degrees C. Under optimized CE-ESI-MS conditions, separation of the investigated drugs was performed in less than 6 min, with a high efficiency. Method precision based on migration time and peak area was determined and the limits of detection, which depend on the tested compound, were established between 20 and 70 ng ml(-1) in the selected ion monitoring mode. Finally, the described method was successfully applied to the analysis of amphetamines in urine after a liquid-liquid extraction.

A poly(ortho ester) designed for combined ocular delivery of dexamethasone sodium phosphate and 5-fluorouracil: subconjunctival tolerance and in vitro release

A viscous hydrophobic poly(ortho ester) (POE) has been developed as a biocompatible, biodegradable sustained release system for selected cases of glaucoma filtering surgery. Dexamethasone and 5-fluorouracil (5-FU) are frequently administered together post-operatively, for their anti-fibroblastic and anti-inflammatory properties, respectively. A combined sustained release of both drugs could be advantageously used. Drug release kinetics were studied using specially designed thermostated cells. Subconjunctival tolerance was evaluated on New Zealand albino rabbits by clinical evaluation. Due to its basicity, the addition of dexamethasone sodium phosphate (DEX-P) stabilized the polymer and prolonged 5-FU in vitro release from 2 to 4 days. Both therapeutic agents were released concomitantly, according to a linear profile. The presence of 5-FU only slightly affected the overall subconjunctival tolerance of POE in rabbits, whereas the addition of DEX-P markedly improved POE tolerance by reducing the hyperemia of the conjunctiva to a minimal grade.

Simultaneous stereoselective analysis of venlafaxine and O-desmethylvenlafaxine enantiomers in clinical samples by capillary electrophoresis using charged cyclodextrins

Capillary electrophoresis (CE) was used for the simultaneous chiral determination of venlafaxine (Vx), a new antidepressant drug and its main active metabolite. O-desmethyl venlafaxine (ODV). Among the charged cyclodextrins (CD) tested, phosphated gamma-CD was the most appropriate. Resolution of Vx and ODV was obtained with 50 mM phosphate buffer (pH 2.5) containing 20 mg/ml of phosphated gamma-CD. After optimisation of the method (including robustness), validation was carried out. Vx and ODV concentrations, as well as the enantiomeric ratio, were investigated in clinical samples. Chiral determination of Vx and ODV was performed after a simple liquid-liquid extraction (LLE). In the tested concentration range (25-500 ng/ml), coefficients of correlation were superior to 0.996. Within-day and between-day accuracy and precision were determined at three different concentrations for each enantiomer. Analyses of clinical samples (n = 16) exhibited non-racemic ratios for Vx and ODV, which suggests a stereoselective metabolism in humans.

Experimental design in supercritical fluid extraction of cocaine from coca leaves

An optimisation procedure for the supercritical fluid extraction (SFE) of cocaine from the leaves of Erythroxylum coca var. coca was investigated by means of experimental design. After preliminary experiments where the SFE rate-controlling mechanism was determined, a central composite design was applied to evaluate interactions between selected SFE factors such as pressure, temperature, nature and percentage of the polar modifier, as well as to optimise these factors. Predicted and experimental contents of cocaine were compared and robustness of the extraction method estimated by drawing response surfaces. The analysis of cocaine in crude extracts was carried out by capillary GC equipped with a flame ionisation detector (GC-FID), as well as by capillary GC coupled with a mass spectrometer (GC-MS) for peak identification.

Chiral stationary phases in HPLC for the stereoselective determination of methadone

An extensive study of the behavior of three chiral stationary phases (CSP) is presented for the stereoselective determination of methadone. The following chromatographic columns were selected: a cellulose, Chiralcel OJ; a modified cyclodextrin. Cyclobond I 2000 RSP, and a protein, Chiral-AGP. Retention factors, enantioselectivity, efficiency, and resolution were tested by modifying the composition of the mobile phase as well as the temperature. The mechanism for the chiral recognition of methadone on each support was discussed. Optimal chromatographic parameters were obtained for the three supports tested, and methadone enantiomers were separated in less than 20 minutes. The cellulose-based column gave the best resolution, but this CSP was not adapted to clinical analyses of methadone. Under optimized conditions, the cyclodextrin- and protein-based columns allowed an excellent separation of methadone enantiomers, but no interference with the primary metabolite was found only with Chiral-AGP.

Development and robustness testing of a nonaqueous capillary electrophoresis method for the analysis of nonsteroidal anti-inflammatory drugs

Nine non steroidal anti-inflammatory drugs were simultaneously separated by nonaqueous capillary electrophoresis with a methanol-acetonitrile (40:60, v/v) mixture containing 20 mM ammonium acetate. The effect of solvent composition, electrolyte nature and concentration on the electrophoretic behavior of the selected drugs was systematically studied. Investigated electrolytes were ammonium, lithium and sodium acetate. Modification of the solvent and/or the electrolyte composition was found to alter the migration order of the pharmaceutical drugs. Finally, to assess method robustness, three sensitive electrophoretic parameters as well as their interactions were evaluated using a full factorial design at two levels.

Enantioselective analysis of methadone in saliva by liquid chromatography-mass spectrometry

Saliva was tested and evaluated as a biological matrix for methadone (Mtd) monitoring. Conventional method using a narrow bore C18 column, and an enantioselective method using a narrow bore alpha1-acid glycoprotein column, were developed using liquid chromatography coupled with a mass spectromeric (MS) detector. After optimisation of MS conditions by flow injection analysis, selected ion monitoring detection was used to enhance sensitivity. The total Mtd concentration and the enantiomeric ratio in saliva were validated using an experimental design. The methods were applied to samples provided by heroin addicts undergoing a Mtd treatment. Results on total Mtd determination showed a very poor correlation between saliva and serum, whereas the enantiomeric ratios of Mtd gave a very good one.

Enantioseparation of atropine by capillary electrophoresis using sulfated beta-cyclodextrin: application to a plant extract

A capillary zone electrophoresis (CZE) method, with sulfated beta-CD as chiral selector, was optimized by means of an experimental design for the enantioseparation of atropine. In this study, a central composite design was used and the following factors were varied simultaneously: buffer concentration, buffer pH and sulfated beta-CD concentration. The resolutions between littorine and its positional isomer ((-)-hyoscyamine) and between atropine enantiomers, as well as the separation time and generated current were established as responses. A model was obtained for each response by linear multiple regression of a second-degree mathematical expression. The most favorable conditions were determined by maximizing the resolution between atropine enantiomers and by setting the other responses at threshold values. Successful results were obtained with a 55 mM phosphate buffer at pH 7 in the presence of 2.9 mM sulfated-beta-CD at 20 degrees C and 20 kV. Under these optimized conditions, a baseline separation of littorine and atropine enantiomers was achieved in less than 5 min. Finally, the method allowed the enantiomeric separation of atropine in a pharmaceutical formulation and was also found to be suitable for the enantiomeric purity evaluation of (-)-hyoscyamine in plant extracts, in relation with the extraction procedure. It was demonstrated that supercritical fluid extraction induced less racemization than classical liquid-solid extraction procedures.

Simultaneous stereoselective analysis of tramadol and its main phase I metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry

On-line combination of partial filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the simultaneous enantioseparation of tramadol and its main phase I metabolites. The partial filling technique was efficient at avoiding MS contamination by the chiral selector. Different experimental factors were investigated, including the chiral selector nature and concentration, plug length as well as the separation temperature. The best enantioseparation of the investigated compounds was achieved with a coated polyvinyl alcohol capillary and a 40 mM ammonium acetate buffer, pH 4.0, adding sulfobutyl ether beta-cyclodextrin (2.5 mg/ml) as the chiral selector. The charged cyclodextrin not only allowed enantioseparation of tramadol and its metabolites, but also improved the selectivity of compounds with the same molecular mass. Finally, CE-electrospray ionisation-MS was successfully applied to the stereoselective analysis of tramadol and its main metabolites in plasma after a simple liquid-liquid extraction.

Experimental design for enantioselective separation of celiprolol by capillary electrophoresis using sulfated beta-cyclodextrin

A capillary zone electrophoresis method was developed for the enantioseparation of celiprolol enantiomers, using a sulfated beta-cyclodextrin (beta-CD) as a chiral selector. The use of a coated capillary was necessary to achieve stable and reproducible enantioseparations. A central composite design was applied to optimize the method and four parameters were selected for this study: the buffer pH, the buffer concentration, the sulfated beta-CD concentration and the temperature. Resolution between celiprolol enantiomers as well as analysis time and generated current were established as responses. For each response, a model was obtained by a second-degree mathematical expression. From the models, the most favorable conditions were determined by optimizing the resolution between celiprolol enantiomers and by setting the two other responses at threshold values. Response surfaces were also used to assess the robustness of the analytical method around the optimal region. Successful results were obtained with a 52 mM acetate buffer at pH 4.0 in the presence of 3.0 mM sulfated beta-CD at a temperature of 19.5 degrees C. Under these optimized conditions, baseline separation of the celiprolol enantiomers was achieved in less than 10 min. The method showed good validation data in terms of precision, accuracy and linearity, and was found to be suitable in determining celiprolol enantiomers in pharmaceutical preparations and in biological fluids.

Capillary electrophoresis-diode array detection--electrospray mass spectrometry for the analysis of selected tropane alkaloids in plant extracts

Capillary zone electrophoresis, coupled to UV and interfaced with electrospray ionization mass spectrometry (ESI-MS), is described for the simultaneous analysis of hyoscyamine and scopolamine. On-line UV detection occurred at 22 cm from the inlet of the capillary and ESI-MS monitoring was performed along the entire length of the capillary (85 cm). An alkaline solution of 40 mM ammonium acetate at pH 8.5 was suitable for the analysis of the alkaloids under consideration. Under the optimized conditions, including CE and ESI-MS parameters, the two alkaloids were resolved within a short time and with very high sensitivity. The differentiation of hyoscyamine and its positional isomer littorine, commonly encountered in plant material, is also presented using up-front collision-induced dissociation. Finally, the developed method was applied to the analysis of these alkaloids in Belladonna leaf extract and in Datura candida x D. aurea hairy root extract.

Nonaqueous versus aqueous capillary electrophoresis for the dosage of N-butylscopolamine in various pharmaceutical formulations

A simple nonaqueous capillary electrophoresis method is described for the separation of several atropine and scopolamine related drugs. The analysis of these pharmaceutical compounds was performed in a methanol-acetonitrile (25/5, v/v) mixture containing 25 mM ammonium acetate and 1 M acetic acid. The robustness was proved using a full factorial design at two levels. The method was validated and successfully applied for the determination of N-butylscopolamine in different pharmaceutical preparations. Results were compared to those obtained by a capillary electrophoresis method based on aqueous media.

Binding constant dependency of amphetamines with various commercial methylated beta-cyclodextrins

Cyclodextrins play an important role in enantioselective separations. They represent the major class of chiral selectors used by capillary electrophoresis. Unfortunately, the purity of commercial cyclodextrins is often not well characterized, and similar selectors sold by various suppliers may show totally different enantioselectivities. In this study, the composition of several commercial methylated-beta-cyclodextrins is evaluated by means of previously developed analytical methods. Then, different calculation methodologies, such as graphical determinations, as well as nonlinear or linear regression approaches, are evaluated in order to calculate the binding constants of inclusion complexes formed by some amphetamine derivatives with methylated-beta-cyclodextrins. The nonlinear curve-fitting methodology proves to be the most suitable for these determinations. Comparisons are made between the different selectors and several hypotheses are proposed concerning the formation of the inclusion complex. Finally, enantiomeric resolutions are evaluated for these selectors and conclusions drawn about the knowledge of selector composition.

Concomitant and controlled release of dexamethasone and 5-fluorouracil from poly(ortho ester)

A viscous bioerodible and hydrophobic poly(ortho ester) has been developed as a biocompatible, sustained drug release system for an ophthalmic application in intraocular proliferative disorders. The combination of wound healing modulators such as 5-fluorouracil and dexamethasone is a major advantage since these drugs act at different stages of these diseases. Since 5-fluorouracil is an acidic, water-soluble compound and dexamethasone exists in three chemical forms, i.e. the water-insoluble base, the highly hydrophobic acetate ester or the basic phosphate salt, it was of interest to investigate whether the physicochemical properties of the drugs have an influence on their release rates, and whether a concomitant and sustained release of both 5-fluorouracil and dexamethasone could be achieved. It has been found that lipophilicity and acidobasicity play a major role in controlling drug release rates and polymer degradation. The combination of 5-fluorouracil and dexamethasone phosphate allows a sustained and concomitant release of both drugs, due to the basic characteristics of the corticosteroid which stabilize the polymer. This system appears to be promising for concomitant and controlled drug delivery aimed at the pharmacological treatment of intraocular proliferative disorders.

Development of validated stereoselective methods for methadone determination in clinical samples

A stereoselective analysis of methadone (Mtd) in whole blood and serum was developed using liquid chromatography on a protein based chiral stationary phase. Liquid-liquid extraction (LLE) and solid phase extraction methods were applied before chromatographic analysis. The extraction procedure, as well as the choice of the biological matrix, showed significant differences in the extraction yield and in the precision of the assays. Serum was selected for this assay and LLE was chosen as the preparation step because of its simplicity and rapidity. The total procedure was validated and applied to clinical samples. Samples taken from 45 heroin-addicted patients were analyzed. A correlation was found between the dose administered and Mtd concentration (total and R-form), but interindividual variability of the total normalized Mtd was seen (concentration varied from 90 to 530 ng/ml). Furthermore, two populations were apparently observed with a mean Mtd concentration of 200 and 475 ng/ml, respectively. Stereoselective analyses showed that more than 50% of the patients presented a nonracemic ratio, and particularly about 25% showed a preferential metabolism of the active R-Mtd enantiomer. Therefore, the stereoselective determination of Mtd is necessary to improve the quality of the treatment of heroin addiction.

Simultaneous stereoselective analysis by capillary electrophoresis of tramadol enantiomers and their main phase I metabolites in urine

Capillary zone electrophoresis was successfully applied to the enantiomeric resolution of racemic tramadol and its six phase I metabolites using carboxymethylated beta-cyclodextrin (CMB) added to the background electrolyte (BGE). Baseline resolution of tramadol and its metabolites was obtained in less than 30 min using a 50 mM phosphate buffer (pH 2.5) containing 5 mM of CMB. Chiral determinations of tramadol and its main three metabolites, O-demethyltramadol (M1), N-demethyltramadol (M2) and O-demethyl-N-demethyltramadol (M5), were performed in urine after a simple double liquid-liquid extraction of 200 microliters of biological material. In the tested concentration range (0.5-20 micrograms/ml, except for M2: 0.5-10 micrograms/ml) coefficients of correlation superior than 0.994 were obtained. Within-day variation determined on three different concentrations for each enantiomers showed accuracies ranging from 95.4% to 103.2%. The relative standard deviation (RSD) of these assays was determined to be less than 10.0%. Day-to-day variation presented accuracies ranging from 96.3% to 106.5% with a RSD less than 9.0%. After oral administration of 100 mg of tramadol hydrochloride to an healthy volunteer, the urinary excretion was monitored during 30 h. About 15% of the dose was excreted as unchanged tramadol. The enantiomeric ratios of all the excreted analytes, T, M1, M2 and M5, were found to be very different to 1.0, showing that a stereoselective metabolism of tramadol clearly occurred.

Development and validation of liquid chromatography and capillary electrophoresis methods for acarbose determination in pharmaceutical tablets

Liquid chromatography and capillary zone electrophoresis, respectively coupled to an evaporative light scattering detector and a UV detector have been developed for the analysis of acarbose without any derivatization procedure. The electrophoretic separation of acarbose anomers was achieved through the manipulation of the working temperature. Both methods were validated and showed good validation data in terms of precision, accuracy and linearity. The validated methods were successfully applied to the dosage of acarbose in commercially available Glucobay tablets.

Capillary electrophoresis for the analysis of tropane alkaloids: pharmaceutical and phytochemical applications

Three capillary electrophoresis methods, using UV detection, were developed for the simultaneous determination of several tropane alkaloids, including atropine, scopolamine and synthetic derivatives. After optimization, the validated capillary zone electrophoresis methods were applied to the determination of these compounds in various pharmaceutical forms, such as ophthalmic and injection solutions, tablets, suppositories and aerosols. Capillary electrophoresis in the micellar mode was found to be more appropriate for the analysis of hyoscyamine and scopolamine in plant material. These two compounds are generally found together with other tropane alkaloids which present similar structures and charge to mass ratio. Furthermore, the separation of positional isomers, such as hyoscyamine and littorine generally encountered in plant extracts, was also considered. The developed method was applied to the analysis of hairy root extracts of Datura candida x Datura aurea, Datura quercifolia and Hyoscyamus albus.

Selectivity manipulation using nonaqueous capillary electrophoresis. Application to tropane alkaloids and amphetamine derivatives

Non-aqueous capillary electrophoresis was investigated for its potential in the analysis of pharmaceutical compounds, namely tropane alkaloids and amphetamine derivatives. The separation of these drugs was compared in aqueous and organic media such as methanol and/or acetonitrile. Selectivity, migration times and efficiency were critically affected by the composition of the methanol/acetonitrile mixture, as well as by the nature and the concentration of the electrolyte. In particular, the migration orders of two positional isomers, littorine and hyoscyamine, were inverted in the presence of trifluoroacetic acid in the nonaqueous medium. The same behavior was observed for amphetamine-methamphetamine and for two methylenedioxyamphetamine derivatives.

Use of cyclodextrins in capillary electrophoresis: resolution of tramadol enantiomers

Capillary zone electrophoresis was successfully applied to the enantiomeric resolution of racemic tramadol. Both uncoated and polyacrylamide-coated capillaries were tested for method optimization using either negatively charged or native cyclodextrins (CD) added to the background electrolyte (BGE). The resolution was strongly influenced by the CD type and concentration as well as by the pH and the concentration of the BGE. Among the CDs tested, carboxymethylated-beta-cyclodextrin allowed the baseline separation of tramadol enantiomers. After the method was optimized, it was validated in a coated capillary for enantiomeric analysis of tramadol enantiomers in pharmaceutical formulation, including specificity and elution order, linearity, accuracy and precision, determination of limit of detection (LOD) and quantification (LOQ), enantiomeric purity linearity, freedom from interference, and stability of sample solutions. Precision at the target concentration was less than 2%, with an accuracy higher than 99%. Furthermore, the method was able to detect 0.3% and to quantify 1% of the minor enantiomer in the presence of the major one at the target value.

2C-B: a new psychoactive phenylethylamine recently discovered in Ecstasy tablets sold on the Swiss black market

This study sought to identify, by means of several analytical methods (GC-MS, HPLC-DAD, CE-DAD, FTIR, and NMR), 4-bromo-2,5-dimethoxyphenethylamine (2C-B), which was found in two sets of tablets obtained from the Swiss black market. Unequivocal identification of 2C-B was only achieved by a combination of mass spectrometric and NMR analysis. Quantitation of 2C-B was performed by HPLC-DAD and CE-DAD. The amounts of 2C-B found in the tablets (3-8 mg) were in the range of the minimum quantity required to induce the effects characteristic of this drug.

Validated capillary electrophoresis method for the determination of atropine and scopolamine derivatives in pharmaceutical formulations

The simultaneous determination of atropine and scopolamine derivatives, which have similar structures, was investigated by using capillary zone electrophoresis. The effects of buffer pH, buffer concentration and hydroxypropyl-beta-cyclodextrin concentration on migration time and resolution of the investigated compounds were systematically studied. The selected electrophoretic buffer consisted of a 80 mM sodium citrate pH 2.5, containing 2.5 mM hydroxypropyl-beta-cyclodextrin as the complexing agent. Quantitative analysis was validated by testing the reproducibility of the method, giving a relative standard deviation less than 1 and 2% for the intermediate precision of migration times and peak area ratios, respectively. The linearity of the method was assessed between 50 and 150% of the theoretical content (coefficient of correlation greater than 0.99). The proposed method was found to be suitable and accurate for the determination of these basic drugs in pharmaceutical preparations.

Automated on-line dialysis and liquid chromatography of methylenedioxylated amphetamines in plasma and serum samples

An automated on-line dialysis coupled to a trace enrichment method has been developed for the separation and quantification of four methylenedioxylated amphetamines in serum and plasma, using liquid chromatography coupled to a fluorimetric detector. The on-line dialysis method was optimized and validated on fresh human serum and plasma samples. This sample preparation method allowed the quantification of methylenedioxylated amphetamines in serum or plasma, at concentrations as low as ca. 10 ng ml-1, with good repeatability, reproducibility and accuracy. The automated on-line dialysis method took less than 30 min. This method was applied to seven toxicological cases and results showed that the concentration of methylenedioxylated amphetamines in blood was in the range of 20-484 ng ml-1.

Optimized release of dexamethasone and gentamicin from a soluble ocular insert for the treatment of external ophthalmic infections

In the case of external ophthalmic infections, repeated instillations of antibiotics are required to reach therapeutic level, above the minimal inhibitory concentration (MIC). An additional administration of a corticosteroid is often needed, in order to limit the precorneal damages caused by the infection. However, repeated administration of a corticosteroid can increase intraocular pressure and thus lead to glaucoma. To overcome the disadvantages of separated and repeated instillations of two products and to avoid the side effects of dexamethasone, a soluble insert containing gentamicin sulfate and dexamethasone phosphate was developed. The new system ensures the concomitant release of the two drugs during the first 10 h of treatment, followed by an adequate concentration of gentamicin sulfate, above the MIC of 4.0 microgram ml-1, during 50 h, due to a combination of gentamicin sulfate with cellulose acetate phthalate, which reduces the solubility of gentamicin.

Development of a capillary zone electrophoresis method for caseinoglycomacropeptide determination

Caseinoglycomacropeptide (CGMP) is a polypeptide of 64 amino acid residues, derived from the C-terminal part of bovine kappa-casein. A sensitive and selective capillary zone electrophoresis method has been developed and validated for the analysis and quantitation of CGMP. Separation is carried out at 30 kV, using an uncoated fused-silica capillary and 20 mM sodium citrate buffer at acidic pH 3.5. The described method allows the separation of various CGMP subcomponents. The validation data proves that the method has the requisite selectivity, sensitivity, reproducibility and linearity for CGMP assay and for quality control during CGMP manufacturing (batch-to-batch reproducibility).

Sensitive and selective determination of methylenedioxylated amphetamines by high-performance liquid chromatography with fluorimetric detection

A rapid, sensitive and selective liquid chromatographic method with fluorimetric detection was developed for the separation and quantification of four methylenedioxylated amphetamines without interference of other drugs of abuse and common substances found in illicit tablets. The method was validated by examining linearity, precision and accuracy as well as detection and quantification limits. Methylenedioxylated amphetamines were quantified in eight tablets from illicit drug seizures and results were quantitatively compared to HPLC-UV analyses. To demonstrate the better sensitivity of the fluorimetric detection, methylenedioxylated amphetamines were analyzed in serum after a liquid-liquid extraction procedure and results were also compared to HPLC-UV analyses.

Extraction of artemisinin and artemisinic acid from Artemisia annua L. using supercritical carbon dioxide

Artemisinin (an antimalaric compound) and its major precursor artemisinic acid, isolated as the active principles of the medicinal plant Artemisia annua L., were extracted by supercritical fluid extraction (SFE) and analyzed by supercritical fluid chromatography (SFC) using a capillary column, coupled with a flame ionization detector (FID). With optimized operating conditions, artemisinin and artemisinic acid were quantitatively extracted at a flow-rate of 2 ml min-1 in less than 20 min. The supercritical fluid was composed of carbon dioxide and 3% methanol with temperature and pressure fixed at 50 degrees C and 15 MPa, respectively. From the kinetic curves, it appears that the extraction of artemisinin is not limited by the diffusion of the analyte from the plant into the extraction fluid but rather by the elution process. These conditions avoided degradation of the analyte and gave clean extracts ready to be analyzed by SFC. The SFE-SFC-FID method was successfully applied to six samples of A. annua containing various concentrations of artemisinin and artemisinic acid. Results were compared with two conventional liquid solvent extraction processes.

Development and validation of a capillary zone electrophoresis method for the determination of atropine, homatropine and scopolamine in ophthalmic solutions

A capillary zone electrophoresis method is described for the simultaneous determination of atropine, homatropine and scopolamine. Successful results were obtained after optimization of the electrophoretic parameters such as buffer composition and pH. The best separation was achieved using a 100 mM Tris-phosphate running buffer at pH 7. The validation data proved that the method had the requisite selectivity, sensitivity, reproducibility and linearity to be used for the assay of these compounds in pharmaceutical formulations. Dosage of the separate drugs in ophthalmic preparations is also presented.

Central composite design in the chiral analysis of amphetamines by capillary electrophoresis

We have studied a central composite design for the chiral separation of amphetamines using capillary electrophoresis. Five variables, i.e., buffer concentration, pH, chiral selector concentration, temperature, and applied voltage, were investigated. Enantiomeric resolutions as well as analysis time and generated power were established as responses for each experiment. A model of each response was obtained by multiple regression of a quadratic-degree mathematical expression. From the models, we determined the most favorable conditions for the chiral separation by optimizing the resolution and setting the other responses at threshold values. Results were compared with a previous study in which a systematic investigation of the operating parameters was carried out. In order to visualize the robustness of the method, response surfaces were drawn for the significant variables. We have concluded that experimental designs offer a rapid means of optimizing several variables and provide an efficient test for the robustness of the analytical method.

Determination of dexamethasone in tears by capillary electrophoresis

A selective capillary zone electrophoresis (CZE) microassay was developed for the simultaneous determination of dexamethasone phosphate and its major metabolite, dexamethasone, in tears. The calibration was carried out in the biological matrix with indoprofen as an internal standard which allowed the separation of dexamethasone phosphate and dexamethasone from the tear constituents. The limits of detection and quantification of the assay were 0.5 and 2.0 microg ml(-1), respectively. This quantification method is essential for the in vivo determination of dexamethasone concentration-time profiles in tears after application of the antiinflammatory drug.

[Ecstasy--the status in French-speaking Switzerland. Composition of seized drugs, analysis of biological specimens and short review of its pharmacological action and toxicity]

Methylenedioxy-N-methylamphetamine (MDMA, "Ecstasy") and other related phenylethylamines are nowadays used extensively in Western Switzerland at dance clubs and raves. There is a widely held belief among teenagers and misusers that ecstasy is safe. In the last years however, an increasing number of reports of MDMA-related deaths has been reported. Acute clinical toxicity problems following MDMA ingestion include hyperthermia, convulsions and arrhythmias. There is also growing concern that these phenylethylamines are neurotoxic and cause long-term damage to serotonineric nerve terminals in animal brains. Qualitative analyses by GC-MS of street samples of ecstasy showed that only a part of them contain MDMA or related phenylethylamines (MDA, MDEA, MBDB and 2C-B). Most of them were mixed with caffeine and an excipient (sugars or polyols [e.g. mannitol]). Amphetamine cut with caffeine and other drugs (e.g. testosterone), stimulants (e.g. pseudoephedrine) and other drugs unrelated to stimulants and phenylethylamines (e.g. LSD, chloroquine, vasodilators) were also detected. Quantitative determinations performed by HPLC-DAD or EC-DAD reveal huge fluctuations in the amount of active substance(s) per tablet. MDMA and related compounds display unique psychoactive properties, acting as a stimulant and inducing feelings of empathy. The effects of MDMA intake are very likely the results of the large release of serotonin (5-HT) in the synaptic cleft, of the inhibition of the re-uptake inactivation of 5-HT and of the inhibition of a key-enzyme involved in the biosynthesis of 5-HT. Forensic investigations performed at our institute showed significant blood levels of MDMA, MDEA and MDA in samples drawn from people suspected of driving under the influence of psychoactive drugs. Up to now, no death could be attributed to MDMA intoxication only because our analyses always revealed the additional presence of toxic amounts of other psychoactive drugs (e.g. opiates, cocaine). Our study shows that because of the variable composition of ecstasy tablets, unpredictable types and amounts of drugs may be taken by MDMA misusers. Moreover, there is considerable concern that traffic accidents may be caused by MDMA-abusers. MDMA intake could result in severe intoxication and even death, especially when combined with other types of drugs.

Detection of human growth hormone doping in urine: out of competition tests are necessary

The misuse of human growth hormone (hGH) in sport is deemed to be unethical and dangerous because of various adverse effects. Thus, it has been added to the International Olympic Committee list of banned substances. Until now, the very low concentration of hGH in the urine made its measurement difficult using classical methodology. Indeed, for routine diagnosis, only plasma measurements were available. However, unlike blood samples, urine is generally provided in abundant quantities and is, at present, the only body fluid allowed to be analysed in sport doping controls. A recently developed enzyme-linked immunosorbent assay (Norditest) makes it now possible, without any extraction, to measure urinary hGH (u-hGH) in a dynamic range of 2-50 ng hGH/l. In our protocol, untreated and treated non-athlete volunteers were followed. Some of them received therapeutical doses of recombinant hGH (Norditropin) for one week either intramuscularly (three increasing doses) or subcutaneously (12 i.u. every day). The u-hGH excretion after treatment showed dramatic increases of 50-100 times the basal values and returned to almost the mean normal level after 24 h. u-hGH was also measured in samples provided by the anti-doping controls at major and minor competitions. Depending on the type of efforts made during the competition, the hGH concentration in urine was dramatically increased. Insulin-like growth factor binding proteins and beta 2-microglobulins in urine and/or in blood could be necessary for the correct investigation of any hGH doping test procedure.

Stereoselective determination of methadone in serum by HPLC following solid-phase extraction on disk

A solid-phase extraction (SPE) technique for methadone has been developed using a mixed-mode solid-phase extraction disk which contains both hydrophobic and cation-exchange functional groups. The SPE technique was used to isolate the drug from the biological matrix and to prepare a cleaner sample prior to stereoselective analysis by HPLC on a silica column with covalently bound alpha 1-acid glycoprotein (Chiral-AGP) followed by ultraviolet detection at 205 mm. The within-run precision was less than 5% for the complete method over the therapeutic range. The quantification limit was 25 ng ml-1. The between-run precision was less than 15% at the quantification limit. The between-run precision at other concentrations was less than 8.5% with an accuracy of more than 95%. The mean recovery for R-methadone was 78.5% and the mean recovery for S-methadone was 73.4%. The complete procedure has been validated. This method was successfully used for the analysis of 15 clinical cases.

Stereoselective interaction between piroxicam and acenocoumarol

1. An open-label study was performed to assess the effect of piroxicam on the pharmacokinetics of acenocoumarol enantiomers. 2. Eight healthy male volunteers received an oral dose of 4 mg rac-acenocoumarol on days 1 and 8, plus 40 mg piroxicam orally 2 h before the anticoagulant on day 8. R- and S-acenocoumarol, piroxicam and their metabolites were measured in plasma over a 24 h interval. 3. The pharmacokinetics of R-acenocoumarol were markedly modified by piroxicam: Cmax+28.0% (s.d.23.8), P < 0.05; AUC(0, 24 h)+47.2% (21.5), P < 0.005; and t1/2 +38.0% (34.5), P < 0.01. A concomitant decrease of CL/F was observed: -30.8% (10.0), P < 0.0001. A similar, but statistically non-significant trend, was observed on the S-enantiomer: Cmax: +9.5% (s.d.36.6), AUC(0, 24 h): + 15.4% (23.4), t1/2: +19.9% (42.0), and CL/F: -9.8% (20.5). V/F remained unchanged for both enantiomers. 4. Piroxicam plasma AUC(0, 24 h) correlated closely with R- and S-acenocoumarol AUCs on day 1 (r = 0.901, P < 0.005 and r = 0.797, P < 0.05, respectively), as well as with the difference of AUC between days 1 and 8 for R-acenocoumarol (r = 0.903, P < 0.001) and S-acenocoumarol (r = 0.711, P < 0.05). 5. Piroxicam markedly reduced acenocoumarol enantiomer clearance, with a greater effect on the more active R-isomer. This interaction, which occurs in addition to the well documented pharmacodynamic one (effect on platelets), is expected to result in increased anticoagulant effect.