Biomedical subjects
Publications and source records attributed to J T Stewart.
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A stability-indicating HPLC method was developed to simultaneously determine cisatracurium besylate and propofol in mixtures. The effects of organic modifier, ionic strength and the pH of the mobile phase on resolution and retention were investigated. A baseline separation was achieved on an octadecylsilane column with an isocratic mobile phase of acetonitrile-ammonium formate (pH 5.2; 0.3 M) (50:50, v/v). Cisatracurium and propofol were confirmed by both retention time and mass-to-charge ratio using LC-MS. The degradation products of cistracurium were identified by ESI positive-ion detection as Hofmann elimination and ester hydrolysis products of cisatracurium. There were no propofol degradation products observed. The quantitation of the two drugs was accomplished using UV detection at 280 nm. This method showed linearity for cisatracurium besylate and propofol in the 9-128 and 37-592 micrograms ml-1 ranges, respectively. Accuracy and precision were in the 0.4-1.4 and 0.4-2.9% ranges respectively, for both analytes.
Mass Spectrometry has been used to determine the identity of a number of degradation products from the bulk drug form of Isradipine (DynaCirc). Liquid chromatography coupled with mass spectrometry (LC/MS) was used to analyze the degraded samples and tentative identifications were made based upon the known reactivity of the molecule, molecular weight measurements and mass spectral fragmentation patterns. Isradipine was found to be stable to heating, acidic and basic conditions, but susceptible to degradation from exposure to UV light and oxidative processes.
A stability indicating, reversed phase high-performance liquid chromatographic method utilizing a smallbore HPLC column has been developed for the determination of clonazepam in a commercial tablet dosage form. The use of a small bore column results in a substantial solvent savings, as well as a greater mass sensitivity, especially in the identification of degradation peaks in a chromatogram. The method involves ultraviolet detection at 254 nm and utilized a 150 x 3.0 mm i.d. column packed with 3 microm octyldecylsilane particles with a mobile phase of water methanol acetonitrile (40:30:30, v/v/v) at a flow rate of 400 microl min(-1) at ambient temperature, with and without the use of 1,2-dichlorobenzene as the internal standard. The current USP method for the analysis of clonazepam using a 300 x 3.9 mm i.d. conventional octyldecylsilane column was utilized as a comparison to the smallbore method. The retention times for clonazepam and the internal standard on the 3.0 mm i.d. column were 4.0 and 12.5 min, respectively. The intra- and interday RSDs on the 3.0 mm i.d. column were < 0.55% (n =4) using the internal standard, and < 0.19% (n = 4) without the internal standard at the lower limit of the standard curve, 50 microg ml(-1) and had a limit of detection of 24 ng ml(-1). The assay using the 3.0 mm i.d. column was shown to be suitable for measuring clonazepam in a tablet dosage form.
OBJECTIVES: This study sought to evaluate a biochemical approach to the early noninvasive assessment of reperfusion. BACKGROUND: In patients with an acute myocardial infarction, a rapid noninvasive method of detecting failure of intravenous thrombolytic therapy to restore early Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow in the infarct-related artery (IRA) is needed. METHODS: Serial blood samples were collected to assay creatine kinase-MB fraction (CKMB mass), cardiac troponin T and myoglobin concentrations in 105 patients with a myocardial infarction who underwent early angiography after intravenous streptokinase. The ratios of the 60- and 90-min concentrations to prethrombolytic values were used to determine an index that could identify failure to achieve TIMI grade 3 flow in the IRA at 90 min. RESULTS: Significant increases in serum concentrations of markers at 60 min were more likely with TIMI grade 3 flow (59 patients) than with TIMI grade 0 to 2 flow (46 patients). Ratios < or = 5 at 60 min after thrombolysis detected failure to achieve 90-min TIMI grade 3 flow with 92% to 97% sensitivity, 43% to 60% specificity and 63% to 76% positive and 86% to 94% negative predictive values. Ratios < or = 10 at 90 min showed 88% to 95% sensitivity, 49% to 65% specificity and 61% to 69% positive and 86% to 94% negative predictive values for TIMI flow grade < 3. The overall predictive values were thus similar for all three markers. CONCLUSIONS: In acute myocardial infarction treated with intravenous streptokinase, a simple measurement of increased serum concentrations of CKMB mass, cardiac troponin T or myoglobin at 60 and 90 min can accurately predict failure to achieve TIMI grade 3 flow in the IRA at 90 min.
Psychiatric and behavioral problems are present in most patients with dementia and are usually the clinician's main focus of management. Differential diagnosis of these problems can be challenging, but the effort is essential for planning appropriate therapy. Pharmacologic interventions are available for treatment of depression, agitation, aggression, psychotic symptoms, wandering, and sleep disorders. Given the less than favorable risk-benefit ratio of most psychotropic drugs in the population of older patients with dementia, the importance of nonpharmacologic strategies and limiting treatment goals should not be overlooked.
A sensitive and stereospecific HPLC method was developed for the analysis of (-)- and (+)-pentazocine in human serum. The assay involves the use of a phenyl solid-phase extraction column for serum sample clean-up prior to HPLC analysis. Chromatographic resolution of the pentazocine enantiomers was performed on a octadecylsilane column with sulfated-beta-cyclodextrin (S-beta-CD) as the chiral mobile phase additive. The composition of the mobile phase was aqueous 10 mM potassium dihydrogenphosphate buffer pH 5.8 (adjusted with phosphoric acid)-absolute ethanol (80:20, v/v) containing 10 mM S-beta-CD at a flow-rate of 0.7 ml/min. Recoveries of (-)- and (+)-pentazocine were in the range of 91-93%. Linear calibration curves were obtained in the 20-400 ng/ml range for each enantiomer in serum. The detection limit based on S/N=3 was 15 ng/ml for each pentazocine enantiomer in serum with UV detection at 220 nm. The limit of quantitation for each enantiomer was 20 ng/ml. Precision calculated as R.S.D. and accuracy calculated as error were in the range 0.9-7.0% and 1.2-6.2%, respectively, for the (-)-enantiomer and 0.8- 7.6% and 1.2-4.6%, respectively, for the (+)-enantiomer (n=3).
A sensitive and stereospecific method for the quantitation of trimipramine enantiomers in human serum was developed. The assay involves the use of a novel mixed-mode disc solid-phase extraction for serum sample clean-up prior to HPLC analysis and is also free of interference from the enantiomers of desmethyltrimipramine, 2-hydroxytrimipramine, and 2-hydroxydesmethyltrimipramine, the three major metabolites of trimipramine. Chromatographic resolution of trimipramine enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OD-R) under isocratic conditions using a mobile phase consisting of 0.3 M aqueous sodium perchlorate-acetonitrile (58:42, v/v) at a flow-rate of 0.5 ml/min. Recoveries for R- and S-trimipramine enantiomers were in the range of 93-96% at 25-185 ng/ml levels. Intra-day and inter-day precisions calculated as R.S.D. were in the ranges of 0.30-8.00% and 1.60-10.20% for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.01-2.10% and 1.00-3.00% ranges for both enantiomers, respectively. Linear calibration curves were in the concentration range 15-250 ng/ml for each enantiomer in serum. The limit of quantification of each enantiomer was 15 ng/ml. The detection limit for each enantiomer in serum using a UV detector set at 210 nm was 10 ng/ml (S/N=2). In addition, separation of the enantiomers of desmethyltrimipramine, 2-hydroxytrimipramine, and 2-hydroxydesmethyltrimipramine were investigated. The desmethyltrimipramine enantiomers could be resolved on the Chiralcel OD-R column under the same chromatographic conditions as the trimipramine enantiomers, but the other two metabolite enantiomers required different mobile phases on the Chiralcel OD-R column to achieve satisfactory resolution with Rs values of 1.00.
Benzene is a ubiquitous occupational hematotoxin and leukemogen, but people vary in their response to this toxic agent. To evaluate the impact of interindividual variation in enzymes that activate (i.e., CYP2E1) and detoxify (i.e., NQO1) benzene and its metabolites, we carried out a case-control study in Shanghai, China, of occupational benzene poisoning (BP; i.e., hematotoxicity), which we show is itself strongly associated with subsequent development of acute nonlymphocytic leukemia and the related myelodysplastic syndromes (relative risk, 70.6; 95% confidence interval, 11.4-439.3). CYP2E1 and NQO1 genotypes were determined by PCR-RFLP, and CYP2E1 enzymatic activity was estimated by the fractional excretion of chlorzoxazone (fe(6-OH)) for 50 cases of BP and 50 controls. Subjects with both a rapid fe(6-OH). and two copies of the NQO1 609C-->T mutation had a 7.6-fold (95% confidence interval, 1.8-31.2) increased risk of BP compared to subjects with a slow fe(6-OH) who carried one or two wild-type NQO1 alleles. In contrast, the CYP2E1 PstI/RsaI polymorphism did not influence BP risk. This is the first report that provides evidence of human susceptibility to benzene-related disease. Further evaluation of susceptibility for hematotoxicity and hematological malignancy among workers with a history of occupational exposure to benzene is warranted.
A stereospecific HPLC method was developed for the assay of R-(-)- and S-(+)-ondansetron enantiomers in human serum. The method involves the use of solid-phase extraction for sample clean-up and is also free of interference from 6-hydroxyondansetron, 7-hydroxyondansetron and 8-hydroxyondansetron, the three major metabolites of ondansetron. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OD-R) under isocratic conditions using a mobile phase consisting of 0.7 M sodium perchlorate-acetonitrile (65:35, v/v) at a flow-rate of 0.5 ml/min. Recoveries at 200 ng/ml levels were more than 90% for both ondansetron enantiomers. Intra-day and inter-day precisions calculated as R.S.D.s were in the 0.3-5% and 2-8% ranges for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.3-11.5% and 0-3% ranges for both enantiomers, respectively. Linear calibration curves were obtained for each enantiomer in serum in the concentration range 15-750 ng/ml. The limit of quantitation of each enantiomer was 15 ng/ml. The detection limit for each enantiomer in serum using UV detection at 210 nm was 7 ng/ml (S/N=2).
A capillary electrophoresis (CE) method for the quantification of R-(-)- and S-(+)-prilocaine in human serum was developed and validated. Stereoselective resolution was accomplished using 15 mM heptakis(2,6-di-methyl)-beta-cyclodextrin and 0.03 mM hexadecyltrimethylammonium bromide (HTAB) contained in 100 mM phosphate buffer, pH 2.5. Solid-phase extraction was used as a sample preparation technique to remove endogenous interferences. A 72-cm uncoated fused-silica capillary at a voltage of 25 kV and 30 degrees C was used for the analysis. The detection limits for R-(-)- and S-(+)-prilocaine were 38 ng/ml using 1 ml of human serum and the limits of quantitation were 45 ng/ml. The calibration curve was linear over the range of 45-750 ng/ml with procainamide as the internal standard. Precision and accuracy of the method were 2.86-8.50% and 3.29-7.40%, respectively, for R-(-)-prilocaine, and 3.94-9.17% and 2.0-6.73%, respectively, for S-(+)-prilocaine. The CE method was compared to an existing chiral HPLC method in terms of sensitivity and selectivity for the routine analysis of the drug.
A sensitive HPLC method for the quantification of praziquantel enantiomers in human serum is described. The method involves the use of a novel disc solid-phase extraction for sample clean-up prior to HPLC analysis and is also free of interference from trans-4-hydroxypraziquantel, the major metabolite of praziquantel. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OJ-R) under isocratic conditions using a mobile phase consisting of 0.1 M sodium perchlorate-acetonitrile (66:34, v/v) at a flow-rate of 0.5 ml/min. Recoveries for R-(-)- and S-(+)-praziquantel enantiomers were in the range of 84-89% at 50-500 ng/ml levels. Intra-day and inter-day precisions calculated as R.S.D. were in the ranges of 3-8% and 1-8% for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.2-5% and 0.3-8% ranges for both enantiomers, respectively. Linear calibration curves were in the concentration range 10-600 ng/ml for each enantiomer in serum. The limit of quantification of each enantiomer was 10 ng/ml. The detection limit for each enantiomer in serum using a UV detector set at 210 nm was 5 ng/ml (S/N=2).
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A high-performance capillary electrophoresis (HPCE) assay method for the quantitation of S-(+)- and R-(-)-ondansetron in human serum was developed. Resolution was achieved using 15 mM heptakis-(2, 6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD) in 100 mM phosphate buffer (pH 2.5). A 72-cm untreated fused-silica capillary, at a constant voltage of 20 kV, was used for the analysis. A 0.03-mM cationic detergent was used as a buffer additive to decrease the adsorption of endogenous substances onto the silica wall. The analytes of interest were isolated from endogenous substances using a solid-phase extraction procedure. The cyanopropyl cartridge gave good recoveries in excess of 85% for both S-(+)- and R-(-)-ondansetron, without any interferences. To decrease the limits of detection of the analytes, an on-capillary sample concentration technique was employed. The detection limit was 10 ng/ml using 2 ml of serum and the limit of quantitation was 15 ng/ml. The calibration curve was linear over a range of 15-250 ng/ml, with procainamide as the internal standard, and the coefficients of determination obtained were greater than 0.999 (n = 3). Precision and accuracy of the method were 2.76-5.80 and 2.10-5.00%, respectively, for S-(+)-ondansetron, and 3.10-6.57 and 2.50-4.35%, respectively, for R-(-)-ondansetron. The HPCE method is a useful alternative to existing chiral high-performance liquid chromatographic methods.
A stereoselective high-performance liquid chromatography assay method was developed for the quantitation of R-(+)- and S-(-)-mepivacaine in human serum. The assay uses a Pirkle brush-type (S)-tert.-leucine, (R)-1-(alpha-naphthyl)ethylamine stationary phase (Sumichiral OA-4700, 250 x 4 mm I.D.) at ambient temperature with a mobile phase of hexane-ethylenedichloride-absolute methanol (85:10:5, v/v) for the separation of R-(+)- and S-(-)-mepivacaine. The eluents were monitored using UV detection at 220 nm. Isolation of the analytes from serum was performed using a 1-ml C18 solid-phase extraction cartridge with high recovery and selectivity. The detection limits were 100 ng/ml for each enantiomer and the limits of quantitation were 150 ng/ml for both enantiomers. Linear calibration curves in the 150-2400 ng/ml range showed good correlation coefficients (r > 0.9994, n = 3). Precision and accuracy of the method were within 2.1-5.3 and 2.0-3.6%, respectively, for R-(+)-mepivacaine and 2.7-5.7% and 1.7-4.2%, respectively, for S-(-)-mepivacaine.
Selected drugs from benzodiazepine, anabolic agent and non-steroidal anti-inflammatory drug (NSAID) therapeutic classes were extracted from water and serum using a supercritical CO2 mobile phase. The samples were extracted at a pump pressure of 329 MPa, an extraction chamber temperature of 45 degrees C, and a restrictor temperature of 60 degrees C. The static extraction time for all samples was 2.5 min and the dynamic extraction time ranged from 5 to 20 min. The analytes were collected in appropriate solvent traps and assayed by modified literature HPLC procedures. Analyte recoveries were calculated based on peak height measurements of extracted vs. unextracted analyte. The recovery of the benzodiazepines ranged from 80 to 98% in water and from 75 to 94% in serum. Anabolic drug recoveries from water and serum ranged from 67 to 100% and 70 to 100%, respectively. The NSAIDs were recovered from water in the 76 to 97% range and in the 76 to 100% range from serum. Accuracy, precision and endogenous peak interference, if any, were determined for blank and spiked serum extractions and compared with classical sample preparation techniques of liquid-liquid and solid-phase extraction reported in the literature. For the benzodiazepines, accuracy and precision for supercritical fluid extraction (SFE) ranged from 1.95 to 3.31 and 0.57 to 1.25%, respectively (n = 3). The SFE accuracy and precision data for the anabolic agents ranged from 4.03 to 7.84 and 0.66 to 2.78%, respectively (n = 3). The accuracy and precision data reported for the SFE of the NSAIDs ranged from 2.79 to 3.79 and 0.33 to 1.27%, respectively (n = 3). The precision of the SFE method from serum was shown to be comparable to the precision obtained with other classical preparation techniques.
A high performance capillary electrophoresis assay for the quantitative determination of R(+) and S(-) mepivacaine in human serum is reported using heptakis (2,6-di-O-methyl) beta-cyclodextrin as the chiral selector for the separation of the enantiomers. The background electrolyte was a 100 mM phosphate buffer (pH 2.5) containing 20 mM heptakis (2,6-di-O-methyl) beta-cyclodextrin and 30 nM hexadecyltrimethylammonium bromide (HTAB). A 72 cm uncoated fused silica capillary was used for the analysis. HTAB was used as the buffer additive to decrease the adsorption of endogenous substances onto the silica wall. To separate the analytes of interest from the endogenous serum substances, a liquid-liquid extraction procedure was used. The extraction recoveries were greater than 70% for both R(+) and S(-) mepivacaine. The detection limits were around 150 ng ml-1 using 1 ml of serum and the limits of quantitation were 200 ng ml-1. The calibration curves were linear over a range of 200-2000 ng ml-1 with R(-) prilocaine as internal standard (IS) and coefficients of determination were greater than 0.999 (n=3). Precision and accuracy of the method were 4.1-7.2 and 2.6-5.9%, respectively, for R(+) mepivacaine and 4.0-7.4 and 3.2-7.4% for respectively, for S(-) mepivacaine. The HPCE method was compared to an existing HPLC method in terms of sensitivity and selectivity for the routine analysis of the drugs.
A direct injection HPLC method has been developed for the determination of phenylbutazone and its active metabolite oxyphenylbutazone in serum using a semipermeable surface (SPS) column. The method is easy to perform and requires 20 microliters of a filtered serum sample. The chromatographic time is less than 13 min using a mobile phase of 15:85 v/v acetonitrile-0.05M phosphate buffer pH 7.5. The method was linear in the range 0.5-20 micrograms ml-1 (r > 0.99, n = 6) with R.S.D. less than 6%. Interday and intraday variability were found to be less than 8.3%. The limit of quantitation and detection were 0.5 and 0.25 microgram ml-1 (s/n > 3), respectively, for both drug and metabolite.