Simultaneous determination of trichloroethylene,perchloroethylene and trichloroacetic acid in human urine using solid-phase microextraction fibre coated with single-walled carbon nanotubes

A reliable and sensitive method for simultaneous determination of perchloroethylene (PCE), trichloroethylene (TCE), and trichloroacetic acid (TCA) in human urine by gas chromatography-mass spectrometry (GC/MS) is described after extraction and preconcentration by a new solid-phase microextraction (SPME) adsorbent. The potential of single-walled carbon nanotubes (SWCNTs) as SPME adsorbent for the pre-concentration of environmental pollutants has been investigated in recent years. This work was carried out to investigate the feasibility of SWCNTs as a headspace SPME adsorbent for the determination of chloroethylenes in human urine. SWCNTs were attached onto a stainless steel wire through an organic binder. Potential factors affecting the extraction efficiency, including extraction time, extraction temperature, desorption time, desorption temperature, and salinity were optimized. The developed method showed good performance. For PCE and TCE, calibration curves were linear (r ^{2 ?}≥?0.994) over the concentration ranges from 15 to 8000?ng?L^?1 and the limit of detection (LOD) at signal-to-noise (S/N) ratio of 3 was 5?ng?L^?1. The analytical procedure also involves derivatization of TCA with dimethyl sulfate, before headspace sampling. For TCA the linear range and LOD were 45-8000 (r ^{2 ?}≥?0.992) and 15?ng L^?1, respectively. In addition, a comparative study between the SWCNT and a commercial carboxen/polydimethylsiloxane (CAR/PDMS) SPME fibre for the determination of chloroethylenes in human urine was carried out. SWCNT fibre showed higher extraction capacity, better thermal stability (over 350°C) and longer life span (over 200 times) than the commercial CAR/PDMS fibre. The developed method was successfully applied to determine chloroethylenes in human urine samples. As the results indicated, the mean concentrations of TCE, PCE and TCA in exposed workers (dry-cleaning industry workers) were significantly greater than that of control group.     

Bioanalytical methods for the determination of antipsychotic drugs

Antipsychotic drugs are popular for the treatment of schizophrenia and other psychoses. In general, antipsychotics are administered in oral doses of only a few milligrams per day and they are widely metabolized in the body. Therefore, the concentration of these drugs in plasma is very low (pg-ng/mL levels). In addition, therapeutic drug monitoring (TDM) of antipsychotic drugs has proven to be of notable value for determining poor compliance of patients and addressing the challenges associated with considerable genetic variability in their metabolism. Thus, in order to conduct pharmacology and toxicology studies and clinical TDM of antipsychotics, as well as address the challenges associated with polypharmacy and drug metabolism, highly sensitive, selective and accurate bioanalytical methods are essential. The most recent studies on the determination of antipsychotics will be reviewed, including separation techniques, sample pretreatment, detectors and validation.     

Simultaneous determination of caffeic acid and its major pharmacologically active metabolites in rat plasma by LC‐MS/MS and its application in pharmacokinetic study

A simple, sensitive and selective high‐performance liquid chromatography electrospray ionization tandem mass spectrometry (LC‐MS/MS) method was developed for simultaneous determination and pharmacokinetic study of caffeic acid (CA) and its active metabolites. The separation with isocratic elution used a mobile phase composed of methanol and water (containing 0.1% formic acid) at a flow rate of 0.2 mL/min. The detection of target compounds was done in selected reaction monitoring (SRM) mode. The SRM detection was operated in the negative electrospray ionization mode using the transitions m/z 179 ([M ? H]^?) → 135 for CA, m/z 193 ([M ? H]^?) → 134.8 for ferulic acid and isoferulic acid and m/z 153 ([M ? H]^?) → 108 for protocatechuic acid. The method was linear for all analytes over the investigated range with all correlation coefficients 0.9931. The lower limits of quantification were 5.0 ng/mL for analytes. The intra‐ and inter‐day precisions (relative standard deviation) were <5.86 and <6.52%, and accuracy (relative error) was between ?5.95 and 0.35% (n = 6). The developed method was applied to study the pharmacokinetics of CA and its major active metabolites in rat plasma after oral and intravenous administration of CA. Copyright © 2014 John Wiley & Sons, Ltd.     

Validated LC–MS/MS method for the simultaneous determination of enalapril maleate,nitrendipine, hydrochlorothiazide,and their major metabolites in human plasma

Hypertension is a major risk factor for atherosclerosis and ischemic heart disease. Most hypertensive patients need a combination of antihypertensive agents to achieve therapeutic goals. A rapid, sensitive, and selective liquid chromatography-tandem mass spectrometric method was developed and validated for simultaneous determination of enalapril maleate (ENA) and its major metabolite enalaprilat (ENAT), nitrendipine (NIT) and its major metabolite dehydronitrendipine (DNIT), and hydrochlorothiazide (HCT) in human plasma using felodipine as an internal standard (IS). The drugs were extracted from plasma using one-step protein precipitation. Chromatographic separation was performed on a Symmetry C₁₈ column, with water and acetonitrile (10:90, v/v) as mobile phase. The detection was carried out using multiple reaction monitoring mode and coupled with electrospray ionization source. Multiple reaction monitoring transitions were m/z 377.1 → 234.1 for ENA, m/z 349.2 → 206.1 for ENAT, m/z 361.2 → 315.1 for NIT, m/z 359 → 331 for DNIT, m/z 295.9 → 205.1 for HCT, and m/z 384.1 → 338 for felodipine (IS). The method was linear over concentration ranges of 1–200, 20–500, 5–200, 2–100, and 5–200 ng/mL for ENA, ENAT, NIT, DNIT, and HCT, respectively, with r² ≥ 0.99. Method validation was performed according to U.S. Food and Drug Administration guidelines. The validated method showed good sensitivity and selectivity and could be applied for therapeutic drug monitoring and bioequivalence studies.     

Optimization, validation and application of a method for the determination of trichloroethylene in rat plasma by headspace solid-phase microextraction gas chromatography mass spectrometry

Trichloroethylene (TCE) is a small halogenated compound that has been used extensively as a metal degreaser and a solvent for the past 100 years. As a result of its widespread use, TCE can be found in the groundwater of about one-third of the hazardous waste sites on the United States Environmental Protection Agency's National Priorities List. Human exposure to TCE in the environmental media is of concern because TCE has been found to be carcinogenic in laboratory animals. This paper describes the development and validation of a HS-SPME-GC/MS method for determination of TCE in rat plasma. The effects of different parameters such as sample volume, extraction and desorption conditions, fiber positions and salt addition were investigated and optimized. The method is rapid, simple, sensitive and requires a very small sample volume. The lower limit of quantitation was 0.25 ng/mL and correlation coefficient (r(2)) values for the linear range of 0.25-100 ng/mL were 0.996 or greater. The precision and accuracy for intra-day and inter-day were better than 8.0%. This validated method was successfully applied to study the toxicokinetic behavior of TCE following low levels of oral administration. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Liquid chromatography high resolution mass spectrometry for the determination of baclofen and its metabolites in plasma: Application to therapeutic drug monitoring

Baclofen is used to manage alcohol dependence. This study describes a simple method using liquid chromatography coupled to high‐resolution mass spectrometry (LC‐HR‐MS) developed in plasma samples. This method was optimized to allow quantification of baclofen and determination of metabolic ratio of its metabolites, an oxidative deaminated metabolite of baclofen (M1) and its glucuronide form (M2). The LC‐HR‐MS method on Exactive® apparatus is a newly developed method with all the advantages of high resolution in full‐scan mode for the quantification of baclofen and detection of its metabolites in plasma. The present assay provides a protein precipitation method starting with 100 μL plasma giving a wide polynomial dynamic range (R ² > 0.999) between 10 and 2000 ng/mL and a lower limit of quantitation of 3 ng/mL for baclofen. Intra‐ and inter‐day precisions were <8.1% and accuracies were between 91.2 and 103.3% for baclofen. No matrix effect was observed. The assay was successfully applied to 36 patients following baclofen administration. Plasma concentrations of baclofen were determined between 12.2 and 1399.9 ng/mL and metabolic ratios were estimated between 0.4 and 81.8% for M1 metabolite and on the order of 0.3% for M2 in two samples.     

A simple,rapid and sensitive liquid chromatography–tandem mass spectrometry method for the determination of dienogest in human plasma and its pharmacokinetic applications under fasting

A simple, rapid and sensitive analytical method using liquid chromatography coupled to tandem mass spectrometry (LC‐MS/MS) detection with positive ion electrospray ionization was developed for the determination of dienogest in human K₂EDTA plasma using levonorgestrel d₆ as an internal standard (IS). Dienogest and IS were extracted from human plasma using simple liquid–liquid extraction. Chromatographic separation was achieved on a Zorbax XDB‐Phenyl column (4.6 × 75 mm, 3.5 µm) under isocratic conditions using acetonitrile–5 mm ammonium acetate (70:30, v/v) at a flow rate of 0.60 mL/min. The protonated precursor to product ion transitions monitored for dienogest and IS were at m/z 312.30 → 135.30 and 319.00 → 251.30, respectively. The method was validated with a linearity range of 1.003–200.896 ng/mL having a total analysis time for each chromatograph of 3.0 min. The method has shown tremendous reproducibility with intra‐ and inter‐day precision (coefficient of variation) <3.97 and 6.10%, respectively, and accuracy within ±4.0% of nominal values. The validated method was applied to a pharmacokinetic study in human plasma samples generated after administration of a single oral dose of 2.0 mg dienogest tablets to healthy female volunteers and was proved to be highly reliable for the analysis of clinical samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Development and validation of a sensitive and high‐throughput LC‐MS/MS method for the simultaneous determination of esomeprazole and naproxen in human plasma

A sensitive and high‐throughput LC‐MS/MS method has been developed and validated for the combined determination of esomeprazole and naproxen in human plasma with ibuprofen as internal standard. Solid‐phase extraction was used to extract both analytes and internal standard from human plasma. Chromatographic separation was achieved in 4.0 min on XBridge C₁₈ column using acetonitrile–25 mM ammonium formate (70:30, v/v) as mobile phase. Mass detection was achieved by ESI/MS/MS in negative ion mode, monitoring at m/z 344.19 → 194.12, 229.12 → 169.05 and 205.13 → 161.07 for esomeprazole, naproxen and IS, respectively. The calibration curves were linear from 3.00 to 700.02 ng/mL for esomeprazole and 0.50 to 150.08 ng/mL for naproxen. The intra‐ and inter‐batch precision and accuracy across four quality control levels met established criteria of US Food and Drug Administration guidelines. The assay is suitable for measuring accurate esomeprazole and naproxen plasma concentrations in human bioequivalence study following combined administration. Copyright © 2013 John Wiley & Sons, Ltd.     

A simple and sensitive LC‐MS/MS method for the determination of sotalol in rat plasma

A sensitive, rapid and robust HPLC method with tandem mass spectrometry (HPLC/MS/MS) detection has been developed and validated for the quantification of sotalol in rat plasma. Plasma samples were precipitated with acetonitrile before analysis. The chromatographic separation was performed on an Atlantis hydrophilic interaction liquid chromatography Silica column (50 × 2.1 mm, 3 µm) with a gradient mobile phase of 10 mm NH₄COOH (containing 0.2% of formic acid) as buffer A and acetonitrile as mobile phase B. Sotalol (m/z 273.2 → 255.1) and atenolol (the internal standard, IS, m/z 267.2 → 190.1) were monitored under positive ionization mode with 5500 QTRAP. Retention time of sotalol and the IS were 2.69 and 3.43 min, respectively. The linear range was 5–500 nm based on the analysis of 0.1 mL of plasma. The intrabatch precision ranged from 1.2 to 6.1%, and the inter‐batch precision was from 3.3 to 6.5%. The coefficient of variation of IS‐normalized matrix factor was 7.6%. Experiments for stability were performed and the analyte was sufficiently stable. A run time of 6 min for each injection made it possible to analyze a high throughput of plasma samples. The assay was successfully applied to the determination of sotalol in rat plasma after a micro‐dose oral administration. Copyright © 2014 John Wiley & Sons, Ltd.     

Validation and application of a liquid chromatography-tandem mass spectrometric method for the determination of GDC-0834 and its metabolite in human plasma using semi-automated 96-well protein precipitation

A liquid chromatographic–tandem mass spectrometric (LC‐MS/MS) method was developed and validated for the determination of GDC‐0834 and its amide hydrolysis metabolite (M1) in human plasma to support clinical development. The method consisted of semi‐automated 96‐well protein precipitation extraction for sample preparation and LC‐MS/MS analysis in positive ion mode using TurboIonSpray® for analysis. D6‐GDC‐0834 and D6‐M1 metabolite were used as internal standards. A linear regression (weighted 1/concentration²) was used to fit calibration curves over the concentration range of 1 – 500 ng/mL for both GDC‐0834 and M1 metabolite. The accuracy (percentage bias) at the lower limit of quantitation (LLOQ) was 5.20 and 0.100% for GDC‐0834 and M1 metabolite, respectively. The precision (CV) for samples at the LLOQ was 3.13–8.84 and 5.20–8.93% for GDC‐0834 and M1 metabolite, respectively. For quality control samples at 3, 200 and 400 ng/mL, the between‐run CV was ≤7.38% for GDC‐0834 and ≤8.20% for M1 metabolite. Between run percentage bias ranged from ?2.76 to 6.98% for GDC‐0834 and from ?6.73 to 2.21% for M1 metabolite. GDC‐0834 and M1 metabolite were stable in human plasma for 31 days at ?20 and ?70°C. This method was successfully applied to support a GDC‐0834 human pharmacokinetic‐based study. Copyright © 2012 John Wiley & Sons, Ltd.     

A high performance liquid chromatography-tandem mass spectrometric method for the determination of mefenamic acid in human plasma: application to pharmacokinetic study

In the present study, the development and validation of an LC‐MS/MS method for quantifying mefenamic acid in human plasma is described. The method involves liquid–liquid extraction using diclofenac as an internal standard (IS). Chromatographic separation was achieved on a Thermo Hypurity C₁₈, 50 × 4.6 mm, 5 µm column with a mobile phase consisting of 2 m m ammonium acetate buffer and methanol (pH 4.5 adjusted with glacial acetic acid; 15:85, v/v) at a flow‐rate of 0.75 mL/min and the total run time was 1.75 min. Analyte was introduced to the LC‐MS/MS using an atmospheric pressure ionization source. Both the drug and IS were detected in negative‐ion mode using multiple reaction monitoring m/z 240.0 → 196.3 and m/z 294.0 → 250.2, respectively, with a dwell time of 200 ms for each of the transitions. The standard curve was linear from 20 to 6000 ng/mL. This assay allows quantification of mefenamic acid at a concentration as low as 20 ng/mL in human plasma. The observed mean recovery was 73% for the drug. The applicability of this method for pharmacokinetic studies has been established after successful application during a 12‐subject bioavailibity study. Copyright © 2012 John Wiley & Sons, Ltd.     

Rapid and cost-effective LC–MS/MS method for determination of hydroxycitric acid in plasma: Application in the determination of pharmacokinetics in commercial Garcinia preparations

Garcinia cambogia is one of the most commonly used anti-obesity dietary supplements, and hydroxycitric acid (HCA) is a major constituent in the commercial preparations of Garcinia. High doses of HCA are often consumed without much awareness of its pharmacokinetic and toxicokinetic parameters, and therefore, a complete understanding of its effects is lacking. The first step in understanding these parameters is the availability of a reliable bioanalytical method. Here, we present the first report on a UPLC–MS/MS method for analysis of HCA in rat plasma after a simplified and cost-effective protein precipitation. Chromatographic separation of the analytes in the supernatant was achieved using hydrophilic interaction liquid chromatography, where mass parameters were optimized and a rapid 5-min quantitative assay was developed. The method was highly sensitive, accurate, precise and linear in the concentration range of 10.5–5000 ng/mL (validated according to the United States Food and Drug Administration guidelines). Further, the method was successfully used to describe the pharmacokinetic profile of HCA in rat plasma after the administration of pure HCA and commercial Garcinia preparations.     

LC‐MS/MS assay for the determination of lurasidone and its active metabolite,ID‐14283 in human plasma and its application to a clinical pharmacokinetic study

The authors proposed a sensitive, selective and rapid liquid chromatography–tandem mass spectrometric (LC‐MS/MS) assay procedure for the quantification of lurasidone and its active metabolite, i.e. ID‐14283 in human plasma simultaneously using corresponding isotope labeled compounds as internal standards as per regulatory guidelines. After liquid–liquid extraction with tert‐butyl methyl ether, the analytes were chromatographed on a C₁₈ column using an optimized mobile phase composed of 5 mm ammonium acetate (pH 5.0) and acetonitrile (15:85, v/v) and delivered at a flow rate of 1.00 mL/min. The assay exhibits excellent linearity in the concentration ranges of 0.25–100 and 0.10–14.1 ng/mL for lurasidone and ID‐14283, respectively. The precision and accuracy results over five concentration levels in four different batches were well within the acceptance limits. Lurasidone and ID‐14283 were found to be stable in battery of stability studies. The method was rapid with the chromatographic run time 2.5 min, which made it possible to analyze 300 samples in a single day. Additionally, this method was successfully used to estimate the in vivo plasma concentrations of lurasidone and ID‐14283 obtained from a pharmacokinetic study in south Indian male subjects and the results were authenticated by conducting incurred samples reanalysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Liquid chromatography tandem mass spectrometry method for the simultaneous stereoselective determination of venlafaxine and its major metabolite,O‐desmethylvenlafaxine,in human plasma

A sensitive, accurate and highly stereoselective assay for the simultaneous determination of venlafaxine (VEN) and its equipotent metabolite, O‐desmethyl venlafaxine (ODV), in human plasma was developed and validated. Analytes were simultaneously extracted from plasma using solid‐phase extraction and detected by tandem mass spectrometry in positive ion mode with a turbo ion spray interface. Deuterium‐labeled VEN and ODV were used as internal standards. Chromatographic separation was performed on a Chiral AGP column, using a time programmed gradient flow with a total run time of 16 min. The method has a lower limit of quantitation of 0.60 ng/mL. The assay was linear over a range 0.60–300.00 ng/mL for both the enantiomers of VEN and ODV, respectively, with coefficient of correlation > 0.99. The extraction recoveries were >77.0% on an average for all the four analytes. The analytes were found stable in plasma through three freeze (?15 °C) and thaw cycles and under storage at room temperature for 8 h, and also in mobile phase at 10 °C for 54 h. The method has shown good reproducibility, with intra‐ and inter‐day variation coefficients < 9%, for all the analytes, and has proved to be very reliable for analysis of VEN and its metabolite in clinical study samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Validation and clinical application of an LC‐ESI‐MS/MS method for simultaneous determination of tolmetin and MED5, the metabolites of amtolmetin guacil in human plasma

A highly sensitive, rapid assay method has been developed and validated for the simultaneous estimation of tolmetin (TMT) and MED5 in human plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive‐ion mode. A simple solid‐phase extraction process was used to extract TMT and MED5 along with mycophenolic acid (internal standard, IS) from human plasma. Chromatographic separation was achieved with 0.2% formic acid–acetonitrile (25:75, v/v) at a flow rate of 0.50 mL/min on an X‐Terra RP₁₈ column with a total run time of 2.5 min. The MS/MS ion transitions monitored were 258.1 → 119.0 for TMT, 315.1 → 119.0 for MED5 and 321.2 → 207.0 for IS. Method validation and clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 20 ng/mL and the linearity was observed from 20 to 2000 ng/mL, for both the anlaytes. The intra‐day and inter‐day precisions were in the range 3.27–4.50 and 5.32–8.18%, respectively for TMT and 4.27–5.68 and 5.32–8.85%, respectively for MED5. This novel method has been applied to a clinical pharmacokinetic study. Copyright © 2010 John Wiley & Sons, Ltd.     

Validated LC‐MS/MS assay for the quantitative determination of vardenafil in human plasma and its application to a pharmacokinetic study

A sensitive high‐performance liquid chromatography–tandem mass spectrometric (HPLC‐MS/MS) assay has been developed for the quantitative analysis of vardenafil in human plasma. Vardenafil and the internal standard, alprazolam, were extracted from 0.2 mL aliquots of alkalinized plasma by a single solvent extraction into hexane : dichloromethane. Reversed‐phase chromatographic separation was affected by gradient elution with mobile phases consisting of 10 mM ammonium formate pH 7.0 (solvent A) and methanol (100%, solvent B), delivered at a flow rate of 0.4 mL/min. The analytes were detected by using an electrospray ion source on a 4000 QTrap triple quadrupole mass spectrometer operating in positive ionization mode. The mass transitions were m/z 489.3 → 312.2 for vardenafil and m/z 309.2 → 281.0 for alprazolam. The assay was linear over the concentration range of 0.2–100 ng/mL, with correlation coefficients ≥0.995. The intra‐ and inter‐day precision was less than 5.4% in terms of relative standard deviation and the accuracy was within 12.7% in terms of relative error. The lower limit of quantitation was set at 0.2 ng/mL. The high sensitivity and acceptable performance of the assay allowed its application to the analysis of plasma samples obtained following the oral administration of vardenafil to healthy male volunteers in a pharmacokinetic study. Copyright © 2009 John Wiley & Sons, Ltd.     

A liquid chromatography-tandem mass spectrometry assay for the determination of nemonoxacin (TG-873870), a novel nonfluorinated quinolone, in human plasma and urine and its application to a single-dose pharmacokinetic study in healthy Chinese volunteers

Nemonoxacin (TG‐873870) is a novel C‐8‐methoxy nonfluorinated quinolone with higher activity than ciprofloxacin, levofloxacin and moxifloxacin against Gram‐positive pathogens including methicillin‐susceptible or methicillin‐resistant Staphylococcus aureus and Streptococcus pneumoniae with various resistant phenotypes. A rapid, sensitive and selective liquid chromatography–tandem mass spectrometric (LC‐MS/MS) method was developed and validated to determine the concentration of nemonoxacin in human plasma and urine. Protein precipitation and liquid–liquid extraction were employed for plasma and urine sample preparations, respectively, and extract was then injected into the system. Separation was performed on a C₁₈ reversed‐phase column using acetonitrile–0.1% formic acid as a mobile phase. Both analyte and internal standard (gatifloxacin) were determined using electrospray ionization and the MS data acquisition via the selected reaction monitoring in positive‐ion mode. The lower limit of quantification was 5 ng/mL and the calibration curves were linear in the concentration range of 5–1000 ng/mL. The accuracy, precision, selectivity, linearity, recovery, matrix effect and stability were validated for TG‐873870 in human plasma and urine. The method was successfully applied to a pharmacokinetic study enrolling 12 healthy Chinese volunteers administered nemonoxacin malate capsules. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of 4-methyl-piperazine-1-carbodithioic acid 3-cyano-3,3-diphenyl-propyl ester hydrochloride and its major metabolites in rat plasma and tissues by LC-MS/MS

4-Methyl-piperazine-1-carbodithioic acid 3-cyano-3,3-diphenylpropyl ester hydrochloride (TM-208) is a newly synthesized compound, which has shown excellent in vivo and in vitro anticancer activity and low toxicity. To investigate the metabolism of TM-208 in rats, in the present study, we administered TM-208 orally to rats and analyzed its metabolites existing in rat plasma and central tissues by LC-MS/MS. Rat plasma and tissue samples were collected before or after a single oral dose (250 mg/kg) of TM-208, then the analytes were extracted from samples by liquid-liquid extraction and analyzed using LC-MS/MS. The structures of proposed metabolites were elucidated according to the rules of drug metabolism and disposition in vivo and the characteristic fragmentation behaviors of TM-208 in ESI-ITMS(n). Five metabolites (M1-M5) were tentatively or assuredly identified: (2-amino-ethyl)-dithiocarbamic acid 3-cyano-3,3-diphenyl-propyl ester (M1), (2-methylamino-ethyl)-dithiocarbamic acid 3-cyano-3,3-diphenyl-propyl ester (M2), 4-methyl-piperazine-1-carbothioic acid S-(3-cyano-3,3-diphenyl-propyl) ester (M3), piperazine-1-carbodithioic acid 3-cyano-3,3-diphenylpropyl ester (M4), and sulfine of (4-methyl-piperazine-1-carbodithioic acid 3-cyano-3,3-diphenylpropyl ester) (M5).     

A validated SIM GC/MS method for the simultaneous determination of dextromethorphan and its metabolites dextrorphan, 3‐methoxymorphinan and 3‐hydroxymorphinan in biological matrices and its application to in vitro CYP2D6 and CYP3A4 inhibition study

Dextromethorphan is used as a probe drug for assessing CYP2D6 and CYP3A4 activity in vivo and in vitro. A SIM GC/MS method without derivatization for the simultaneous determination of dextromethorphan and its metabolites, dextrorphan, 3‐methoxymorphinan and 3‐hydroxymorphinan, in human plasma, urine and in vitro incubation matrix was developed and validated. Calibration curves indicated good linearity with a coefficient of variation (r) better than 0.995. The lower limit of quantitation was found to be 10 ng/mL for all analytes in all matrices. Intra‐day and inter‐day precision for dextromethorphan and its metabolites was better than 9.02 and 9.91%, respectively and accuracy ranged between 91.76 and 106.27%. Recovery for dextromethorphan, its metabolites and internal standard levallorphan was greater than 72.68%. The method has been successfully applied for the in vitro inhibition of metabolism of dextromethorphan by CYP2D6 and CYP3A4 using known inhibitors of CYPs such as quinidine and verapamil. Copyright © 2009 John Wiley & Sons, Ltd.     

A validated LC-MS/MS method for the determination of vinflunine in plasma and its application to pharmacokinetic studies

A rapid, simple and sensitive LC‐MS/MS method for the quantification of vinflunine in plasma was developed and validated. The analysis involved a simple liquid–liquid extraction. After making alkaline with NaOH, plasma was extracted with methyl tert‐butyl ether and the organic extract was then evaporated and the residue was reconstituted in mobile phase. The reconstituted solution was injected into an HPLC system and was subjected to reverse‐phase HPLC on a 5 µm ODS‐3 column at a flow‐rate of 0.2 mL/min. The mobile phase consisted of ammonium acetate (0.02 mol/L, pH = 3.0) and acetonitrile (20:80). Vinflunine was detected in the single ion monitoring mode using target ions at m/z 817.4/160.1/142.3 for vinflunine and m/z 447.2/128.3/112.1 for gefitinib (internal standard). Standard curves were linear over the concentration range of 5–1000 ng/mL. The mean predicted concentrations of the quality control samples deviated by less than 2% from the corresponding nominal values; the intra‐assay and inter‐assay precisions of the assay were within 7% relative standard deviation. The extraction recovery of vinflunine was more than 80%. The validated assay was applied to a pharmacokinetic study of vinflunine in plasma following the administration of a single vinflunine injection (2 mg/kg). Copyright © 2011 John Wiley & Sons, Ltd.