Pharmacokinetic and tissue distribution of paclitaxel in rabbits assayed by LC‐UV after intravenous administration of its novel liposomal formulation

A simple, rapid and sensitive LC‐UV method was developed and validated for the determination of paclitaxel (PTX) in rabbit plasma and tissues. A 2 mL aliquot of acetonitrile and 10 μL ammonium acetate (pH 5.0, 6 m ) as extraction agents were used to markedly increase the extraction recoveries and greatly reduce the endogenous substances. The separation was achieved on a C₁₈ column at 30 °C using an acetonitrile–ammonium acetate buffer (pH 5.0, 0.02 m ; 55:45, v/v) at a flow rate of 1.0 mL/min; UV detection was used at 227 nm. Good linearity was obtained between 0.025 and 10,000 µg/mL for plasma and between 0.025–200,000 µg/g for tissue samples (r > 0.999). The limit of detection was 6 ng/mL in plasma, 8 ng/g in heart and 12.5 ng/g in other tissues. The limit of quantitation was 25 ng/mL in plasma and heart, 125 ng/g in other tissues. The intra‐ and inter‐day assays of precision and accuracy for all bio‐samples ranged from 1.38 to 9.60% and from 83.6 to 114.5%, respectively. The extraction recoveries ranged from 70.1 to 109.5%. Samples were stable during three freeze–thaw cycles or stored in a freezer at ?20 °C for 30 days. The assay method was successfully applied to a study of the pharmacokinetics and tissue distribution of novel PTX lung targeting liposomes. Copyright © 2013 John Wiley & Sons, Ltd.     

Development and validation of LC‐MS/MS method for the estimation of β‐hydroxy‐β‐methylbutyrate in rat plasma and its application to pharmacokinetic studies

A simple, sensitive and specific high‐performance liquid chromatography mass spectrometry (LC‐MS/MS) method was developed and validated for the quantification of β‐hydroxy‐β‐methyl butyrate (HMB) in small volumes of rat plasma using warfarin as an internal standard (IS). The API‐4000 LC‐MS/MS was operated under the multiple reaction‐monitoring mode using the electrospray ionization technique. A simple liquid–liquid extraction process was used to extract HMB and IS from rat plasma. The total run time was 3 min and the elution of HMB and IS occurred at 1.48 and 1.75 min respectively; this was achieved with a mobile phase consisting of 0.1% formic acid in a water–acetonitrile mixture (15:85, v/v) at a flow rate of 1.0 mL/min on a Agilent Eclipse XDB C₈ (150 × 4.6, 5 µm) column. The developed method was validated in rat plasma with a lower limit of quantitation of 30.0 ng/mL for HMB. A linear response function was established for the range of concentrations 30–4600 ng/mL (r > 0.998) for HMB. The intra‐ and inter‐day precision values for HMB were acceptable as per Food and Drug Administration guidelines. HMB was stable in the battery of stability studies, viz. bench‐top, autosampler freeze–thaw cycles and long‐term stability for 30 days in plasma. The developed assay method was applied to a bioavailability study in rats. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous determination of baicalin,oroxylin A‐7‐O‐glucuronide and wogonoside in rat plasma by UPLC‐DAD and its application in pharmacokinetics of pure baicalin,Radix Scutellariae and Yinhuang granule

A novel UPLC‐DAD method was developed and validated for the simultaneous determination of baicalin (baicalein‐7‐glucuronide, BG), oroxylin A‐7‐O‐glucuronide (OAG) and wogonoside (WG) in rat plasma using rutin as the internal standard. Plasma samples were precipitated using acetonitrile containing 0.1% formic acid. Separation was performed on an Agilent Eclipse Plus C₁₈ column (2.1 × 50 mm, 1.8 µm) using gradient acetonitrile and 0.2% formic acid water solution as mobile phase. The flow‐rate was set at 0.4 mL/min and the eluate was detected at 275 nm. The method was linear over the ranges of 0.075–17.50, 0.050–12.60 and 0.056–14.10 µg/mL for BG, OAG and WG, respectively. The intra‐ and inter‐day precisions were respectively <4.8% and 6.4%. All of the limits of detection of three analytes in rat plasma were 0.01 µg/mL, whereas the limits of quantification were, respectively, 0.035, 0.025 and, 0.025 µg/mL. This assay has been successfully applied to pharmacokinetics of BG, OAG and WG in rats after oral administration of Yinhuang granule (YHG) and comparative pharmacokinetics of BG in rats following oral administration of the pure BG, Radix Scutellariae (RS) or YHG. We speculate that some co‐existing ingredients in RS or YHG may increase the absorption and elimination of BG in rat. This work may be helpful for the quality control of Yinhuang granule. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of a novel nonfluorinated quinolone,nemonoxacin, in human feces and its glucuronide conjugate in human urine and feces by high‐performance liquid chromatography–triple quadrupole mass spectrometry

Three methods were developed and validated for determination of nemonoxacin in human feces and its major metabolite, nemonoxacin acyl‐β‐ d ‐glucuronide, in human urine and feces. Nemonoxacin was extracted by liquid–liquid extraction in feces homogenate samples and nemonoxacin acyl‐β‐ d ‐glucuronide by a solid‐phase extraction procedure for pretreatment of both urine and feces homogenate sample. Separation was performed on a C₁₈ reversed‐phase column under isocratic elution with the mobile phase consisting of acetonitrile and 0.1% formic acid. Both analytes were determined by liquid chromatography–tandem mass spectrometry with positive electrospray ionization in selected reaction monitoring mode and gatifloxacin as the internal standard. The lower limit of quantitation (LLOQ) of nemonoxacin in feces was 0.12 µg/g and the calibration curve was linear in the concentration range of 0.12–48.00 µg/g. The LLOQ of the metabolite was 0.0010 µg/mL and 0.03 µg/g in urine and feces matrices, while the linear range was 0.0010–0.2000 µg/mL and 0.03–3.00 µg/g, respectively. Validation included selectivity, accuracy, precision, linearity, recovery, matrix effect, carryover, dilution integrity and stability, indicating that the methods can quantify the corresponding analytes with excellent reliability. The validated methods were successfully applied to an absolute bioavailability clinical study of nemonoxacin malate capsule. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantitative HPLC method and pharmacokinetic studies of ergosta‐4,6,8(14),22‐tetraen‐3‐one,a natural product with diuretic activity from Polyporus umbellatus

A simple and specific HPLC method with dual wavelength UV detection for the determination of ergosta‐4,6,8(14),22‐tetraen‐3‐one (ergone) in rat plasma was developed and proved to be efficient. The method used ergosterol as internal standard (IS). Following a single‐step protein precipitation, the analyte and IS were separated on an Inertsil ODS‐3 column with a mobile phase containing methanol–water (99:1, v/v) at a flow rate of 1 mL/min. The analytes were detected by using UV detection at wavelength of 350 (ergone) and 283 (IS) nm, respectively. The calibration curve was linear over the range of 0.1–2.0 µg/mL and the lower limit of quantification was 0.1 µg/mL. The intra‐day and inter‐day precision studies showed good reproducibility with RSD less than 8.5%. The intra‐day and inter‐day accuracy ranged from 95.6 to 104%. Mean extraction recovery was above 95% at the low, medium and high concentrations. The present HPLC‐UV method was simple and reliable. The method described herein had been successfully applied for the pharmacokinetic studies in male SD rats after administration of 20 mg/kg dose of solution of ergone. Copyright © 2010 John Wiley & Sons, Ltd.     

A high‐performance liquid chromatographic analysis and preliminary pharmacokinetic characterization of 3′‐hydroxypterostilbene in rats

A high‐performance liquid chromatographic method was developed for the analysis of 3'‐hydroxypterostilbene. This method involves the use of a Luna^® C₁₈ column with ultraviolet detection at 325 nm. The mobile phase consisted of acetonitrile, water and formic acid (50:50:0.01, v/v/v) with a flow rate of 0.8 mL/min. The calibration curves were linear over the range 0.5–100.0 µg/mL. The mean extraction efficiency was between 97.40 and 111.16%. The precision of the assay was 0.196–14.39% (RSD%), and within 15% at the limit of quantitation (0.5 µg/mL). The bias of the assay was <16% and within 15% at the limit of quantitation. This assay was successfully applied to pre‐clinical pharmacokinetic samples from rat urine and serum. Copyright © 2009 John Wiley & Sons, Ltd.     

UPLC‐MS/MS assay for the simultaneous quantification of carvedilol and its active metabolite 4′‐hydroxyphenyl carvedilol in human plasma to support a bioequivalence study in healthy volunteers

An ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC‐MS/MS) method has been developed for the simultaneous determination of carvedilol and its pharmacologically active metabolite 4′‐hydroxyphenyl carvedilol in human plasma using their deuterated internal standards (IS). Samples were prepared by solid‐phase extraction using 100 μL human plasma. Chromatographic separation of analytes was achieved on UPLC C18 (50 × 2.1 mm, 1.7 µm) column using acetonitrile‐4.0 mm ammonium formate, pH 3.0 adjusted with 0.1% formic acid (78:22, v/v) as the mobile phase. The multiple reaction monitoring transitions for both the analytes and IS were monitored in the positive electrospray ionization mode. The method was validated over a concentration range of 0.05–50 ng/mL for carvedilol and 0.01‐10 ng/mL for 4′‐hydroxyphenyl carvedilol. Intra‐ and inter‐batch precision (% CV) and accuracy for the analytes varied from 0.74 to 3.88 and 96.4 to 103.3% respectively. Matrix effect was assessed by post‐column analyte infusion and by calculation of precision values (coefficient of variation) in the measurement of the slope of calibration curves from eight plasma batches. The assay recovery was within 94–99% for both the analytes and IS. The method was successfully applied to support a bioequivalence study of 12.5 mg carvedilol tablets in 34 healthy subjects. Copyright © 2013 John Wiley & Sons, Ltd.     

Simultaneous determination of niacin and its metabolites—nicotinamide,nicotinuric acid and N‐methyl‐2‐pyridone‐5‐carboxamide—in human plasma by LC‐MS/MS and its application to a human pharmacokinetic study

An LC‐MS/MS method for the simultaneous quantitation of niacin (NA) and its metabolites, i.e. nicotinamide (NAM), nicotinuric acid (NUA) and N‐methyl‐2‐pyridone‐5‐carboxamide (2‐Pyr), in human plasma (1 mL) was developed and validated using nevirapine as an internal standard (IS). Extraction of the NA and its metabolites along with the IS from human plasma was accomplished using a simple liquid–liquid extraction. The chromatographic separation of NA, NAM, NUA, 2‐Pyr and IS was achieved on a Hypersil‐BDS column (150 ¥ 4.6 mm, 5 mm) column using a mobile phase consisting of 0.1% formic acid : acetonitrile (20:80 v/v) at a flow rate of 1 mL/min. The total run time of analysis was 2 min and elution of NA, NAM, NUA, 2‐Pyr and IS occurred at 1.37, 1.46, 1.40, 1.06 and 1.27 min, respectively. A detailed validation of the method was performed as per the FDA guidelines and the standard curves were found to be linear in the range of 100–20000 ng/mL for NA; 10–1600 ng/mL for NUA and NAM and 50–5000 ng/mL for 2‐Pyr with mean correlation coefficient of ≥0.99 for each analyte. The method was sensitive, specific, precise, accurate and suitable for bioequivalence and pharmacokinetic studies. The developed assay method was successfully applied to a pharmacokinetic study in humans. Copyright © 2010 John Wiley & Sons, Ltd.     

Liquid chromatography–mass spectrometry for the simultaneous determination of the catalpol‐related iridoid glucosides,verproside, isovanilloylcatalpol,catalposide and 6‐O‐veratroyl catalpol in rat plasma

Verproside, isovanilloylcatalpol, catalposide and 6‐O‐veratroyl catalpol are bioactive iridoid glucosides isolated from in a number of folk medicinal plants. A rapid, sensitive and selective liquid chromatography/mass spectrometric (LC/MS) method for the simultaneous determination of verproside, isovanilloylcatalpol, catalposide and 6‐O‐veratroyl catalpol in rat plasma was developed. The analytes were extracted from 50 µL of rat plasma with ethyl acetate using 7‐carboxymethyloxy‐3',4',5‐trimethoxyflavone as internal standard and analyzed on an X‐Bridge C₁₈ column within 6.5 min with 40% methanol in 10 mm ammonium formate (pH 3.0). The analytes were quantified using an electrospray ionization mass spectrometry in the selected ion monitoring mode. The standard curves were linear over the concentration ranges of 10–2000 ng/mL for verproside, isovanilloylcatalpol and catalposide and 20–2000 ng/mL for 6‐O‐veratroyl catalpol. The coefficients of variation and relative errors of verproside, isovanilloylcatalpol, catalposide and 6‐O‐veratroyl catalpol for intra‐ and inter‐assay at four quality control levels were 2.5–8.0 and–4.0–6.6%, respectively. This method was successfully applied to the pharmacokinetic study of verproside and its possible metabolite isovanilloylcatalpol after intravenous administration of verproside, a candidate anti‐asthma drug, in male Sprague–Dawley rats. Copyright © 2009 John Wiley & Sons, Ltd.     

Development and validation of a highly sensitive LC‐MS/MS method for simultaneous quantitation of nortriptyline and 10‐hydroxynortriptyline in human plasma: application to a human pharmacokinetic study

A highly sensitive and specific LC‐MS/MS method has been developed for simultaneous estimation of nortriptyline (NTP) and 10‐hydroxynortriptyline (OH‐NTP) in human plasma (250 µL) using carbamazepine as an internal standard (IS). LC‐MS/MS was operated under the multiple reaction‐monitoring mode using the electrospray ionization technique. A simple liquid–liquid extraction process was used to extract NTP, OH‐NTP and IS from human plasma. The total run time was 2.5 min and the elution of NTP, OH‐NTP and IS occurred at 1.44, 1.28 and 1.39 min, respectively; this was achieved with a mobile phase consisting of 20 mm ammonium acetate : acetonitrile (20:80, v/v) at a flow rate of 0.50 mL/min on a HyPURITY C₁₈ column. The developed method was validated in human plasma with a lower limit of quantitation of 1.09 ng/mL for both NTP and OH‐NTP. A linear response function was established for the range of concentrations 1.09–30.0 ng/mL (r > 0.998) for both NTP and OH‐NTP. The intra‐ and inter‐day precision values for NTP and OH‐NTP met the acceptance as per FDA guidelines. NTP and OH‐NTP were stable in a battery of stability studies, i.e. bench‐top, auto‐sampler and freeze–thaw cycles. The developed assay was applied to a pharmacokinetic study in humans. Copyright © 2010 John Wiley & Sons, Ltd.     

Simultaneous determination of corosolic acid and euscaphic acid in the plasma of normal and diabetic rat after oral administration of extract of Potentilla discolor Bunge by high‐performance liquid chromatography/electrospray ionization mass spectrometry

Potentilla discolor Bunge has been used for diabetes in China for a long time. Corosolic acid (CA) and euscaphic acid (EA), with significant anti‐diabetic activity, are two major triterpenoids in P. discolor. In this study, a specific, sensitive and convenient LC‐MS method has been developed for simultaneous determination of CA and EA in the plasma of normal and diabetic rats after oral administration of the extract of P. discolor. The chromatographic separation was achieved using an Alltima C₁₈ column (53 × 7.0 mm, i.d., 3 µm) with a mobile phase composed of 0.1% formic acid water and 0.1% formic acid acetonitrile at a flow rate of 1.0 mL/min. The detection was performed by MS with electrospray ionization interface in negative selected ion monitoring mode. All the validation data, such as specificity, linearity (r² > 0.9991 within 0.025–10.0 µg/mL), lower limit of quantitation (2.5 ng/mL), precision (intra‐ and inter‐day <14.7%), accuracy (<15.0%), recovery (85.7–110.8%) and stability were determined and all of them were within the required limits. This method was successfully applied for the evaluation of the pharmacokinetic behaviors of these two compounds in the plasma of normal and diabetic rats. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantification and validation of HPLC‐UV and LC‐MS assays for therapeutic drug monitoring of ertapenem in human plasma

Rapid and simple HPLC‐UV and LC‐MS methods were developed and validated for the quantification of ertapenem (Invanz?) in human plasma. Ertapenem is a unique drug in that current dosing recommendations call for a 1 g dose for normal renal function patients, despite body weight. These assays, which involve a protein precipitation followed by liquid–liquid extraction, allow for fast therapeutic drug monitoring of ertapenem in patients, which is especially useful in special populations. Both methods were sufficient to baseline resolve meropenem (internal standard) and ertapenem, and were validated over 3 days using a six‐point calibration curve (0.5–50 µg/mL). Validation was collected using four different points on the calibrations curve yielding acceptable precision (<15% inter‐day and intra‐day; <20% for lower limit of quantitation, LLOQ) as well as accuracy (<15% inter‐day and intra‐day; <20% for LLOQ). The lower limit of detection (LOD) was determined to be 0.1 and 0.05 µg/mL for the HPLC‐UV and LC‐MS methods, respectively. The developed HPLC‐UV and LC‐MS methods for ertapenem quantification are fast, accurate and reproducible over the calibration range and can be used to determine ertapenem plasma concentrations for monitoring clinical efficacy. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantitative determination of metformin,glyburide and its metabolites in plasma and urine of pregnant patients by LC‐MS/MS

This report describes the development and validation of an LC‐MS/MS method for the quantitative determination of glyburide (GLB), its five metabolites (M1, M2a, M2b, M3 and M4) and metformin (MET) in plasma and urine of pregnant patients under treatment with a combination of the two medications. The extraction recovery of the analytes from plasma samples was 87–99%, and that from urine samples was 85–95%. The differences in retention times among the analytes and the wide range of the concentrations of the medications and their metabolites in plasma and urine patient samples required the development of three LC methods. The lower limit of quantitation (LLOQ) of the analytes in plasma samples was as follows: GLB, 1.02 ng/mL; its five metabolites, 0.100–0.113 ng/mL; and MET, 4.95 ng/mL. The LLOQ in urine samples was 0.0594 ng/mL for GLB, 0.984–1.02 ng/mL for its five metabolites and 30.0 µg/mL for MET. The relative deviation of this method was <14% for intra‐day and inter‐day assays in plasma and urine samples, and the accuracy was 86–114% in plasma, and 94–105% in urine. The method described in this report was successfully utilized for determining the concentrations of the two medications in patient plasma and urine. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessment of pharmacokinetic interaction between piracetam and l‐carnitine in healthy subjects

A rapid, sensitive and specific method for quantifying piracetam in human plasma using Piracetam d‐8 as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by one‐step precipitation of protein using an acetonitrile (100%). The extracts were analyzed by high‐performance liquid chromatography coupled with electrospray tandem mass spectrometry (HPLC‐MS/MS). The method had a chromatographic run time of 3.8 min and a linear calibration curve over the range 0.5–50 µg/mL (r > 0.99). This LC‐MS‐MS procedure was used to assess the bioavailability of two piracetam formulations: piracetam + l‐carnitine (Piracar®; 270/330 mg tablet) and piracetam (Nootropil®; 800 mg tablet) in healthy volunteers of both sexes. The geometric means with corresponding 90% confidence interval (CI) for test/reference percentage ratios were 88.49% (90% CI = 81.19 – 96.46) for peak concentration/dose and 102.55% (90% CI = 100.62 – 104.51) for AUC_inf/dose. The limit of quantitation of 0.5 µg/mL is well suited for pharmacokinetic studies in healthy volunteers. It was concluded that piracetam (Piracar®; 270/330 mg tablet) has a bioavailability equivalent to the piracetam (Nootropil®; 800 mg tablet) formulation with regard to both the rate and the extent of absorption. Copyright © 2015 John Wiley & Sons, Ltd.     

Toxicological screening of human plasma by on‐line SPE‐HPLC‐DAD: identification and quantification of basic drugs and metabolites

An automated multi‐analyte screening method for the identification and quantification of 92 drugs and metabolites based on on‐line solid‐phase extraction–high‐performance liquid chromatography–diode array detection technique was developed and successfully validated. In addition, a database with 870 entries including UV‐spectra, relative/retention times and response factors of toxicologically relevant compounds was created. Plasma samples (0.2 mL) were treated with methanol, diluted with buffer and on‐line extracted (Strata X, 20 ×2 mm, 25 µm) at pH 9. Analytical separation was carried out on a Gemini NX column (150 ×4.6 mm, 3 µm) using gradient elution with acetonitrile–water (90:10,v/v) and 0.05 m potassium dihydrogen phosphate buffer (pH 2.3). Linear calibration curves with correlation coefficients ≥0.9950 were obtained for 78 analytes. As an additional benefit, the newly developed method allows the quantification of 42 analytes (e.g. antidepressants, neuroleptics and anticonvulsants) in a concentration range suitable for therapeutic drug monitoring. Limits of quantitation ranged from 0.02 mg/L (chlordiazepoxide) to 3.4 mg/L (mexiletine). Inter‐ and intra‐day precisions of quality control samples (low/high) were better than 15% (zolpidem) and accuracy (bias) ranged from ?11% (opipramol, venlafaxine) to 11% (venlafaxine, trazodone). Tests for carry‐over and sample stability under different storage conditions were also performed and stability was adequate. Four cases of poisoning analysis are presented. Copyright © 2014 John Wiley & Sons, Ltd.     

HPLC method development and validation of cytotoxic agent phenyl‐heptatriyne in Bidens pilosa with ultrasonic‐assisted cloud point extraction and preconcentration

Extraction and pre‐concentration of a bioactive marker compound, phenyl‐1,3,5‐heptatriyne from Bidens pilosa, prior to HPLC has been demonstrated using both organic and ecofriendly solvents. Non‐ionic surfactants, viz. Triton X‐100, Triton X‐114 and Genapol X‐80, were used for extraction. No back‐extraction or liquid chromatographic steps were required to remove the target phytochemical from the surfactant‐rich extractant phase. The optimized cloud point extraction procedure has been shown to be a potentially useful methodology for the preconcentration of the target analyte, with a preconcentration factor of 4–99. Moreover, the method is simple, sensitive, rapid and consumes lesser solvent than traditional methods. An isocratic chromatographic separation and quantitation was accomplished on a C₁₈ column with acetonitrile–acidified aqueous as mobile phase at a flow rate of 1.0 mL/min, UV detection at 254 nm and specificity with photo diode‐array detector (PDA) and MS. Under the optimum experimental conditions recovery was satisfactory (99.18–100.33%) without interference from the surfactant. The method seems to be reliable with intraday precision and interday precision below 2.0%. Good linearity was obtained in the working range from 7.5 to 30 µg/mL with correlation coefficient >0.99. The limits of detection and quantitation were 1.84 and 6.13 µg/mL, respectively. The method was validated following international guidelines and successfully applied for quantitative assays of cytotoxic compound phenyl‐1,3,5‐heptatriyne in Bidens pilosa. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparative pharmacokinetics of cyclophosphamide administration alone and combination with vitamin B6 in rats

A fast and sensitive high performance liquid chromatography coupled with mass spectrometry (LC‐MS) method was developed and validated for the determination of cyclophosphamide in rat plasma with and without the combination of vitamin B6. After addition of digoxin used as the internal standard (IS), plasma samples were extracted by protein precipitation with acetonitrile (1:1, v/v), and the analytes were separated by a Kromasil C₁₈ column (150 × 4.6 mm, 5 µm) with a mobile phase of acetonitrile–0.1% formic acid water (40:60, v/v). The detection of the analyte was monitored in positive electrospray ionization by selected ion monitoringmode. The linear range was 0.01–40 µg/mL for cyclophosphamide. The intra‐ and inter‐day precision and accuracy were all <15%. The extraction recoveries and matrix effects of the analyte and IS were all within acceptable range. The selectivity of the method was satisfactory with no endogenous interference. The results for stabilities of cyclophosphamide and IS under various conditions were all within the acceptance criteria. The validated method was successfully applied to evaluate the drug–drug interaction of cyclophosphamide and vitamin B6 in rat plasma. The results showed no differences of pharmacokinetic behaviors between cyclophosphamide administration with and without vitamin B6. Copyright © 2014 John Wiley & Sons, Ltd.     

Liquid chromatography–tandem mass spectrometry method for simultaneous quantification of urapidil and aripiprazole in human plasma and its application to human pharmacokinetic study

A sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated for simultaneous determination of urapidil and aripiprazole in human plasma. A simple liquid–liquid extraction with ethyl acetate was used for the sample preparation. Chromatographic separation was achieved on a Phenomenex C₁₈ (4.6 × 50 mm, 5 µm) column with 0.1% formic acid–acetonitrile (10:90, v/v) as the mobile phase with flow rate of 0.6 mL/min. The quantitation of the target compounds was determined in a positive ion multiple reaction monitoring mode. Calibration plots were linear over the range of 2.0–2503.95 ng/mL for urapidil and 1.0–500.19 ng/mL for aripiprazole. The lower limit of quantitation for urapidil and aripiprazole was 2.0 and 1.0 ng/mL, respectively. Mean recovery was in the range of 69.94–75.62% for both analytes and internal standards. Intra‐day and inter‐day precisions of the assay at three concentrations were 2.56–5.89% with accuracy of 92.31–97.83% for urapidil, and 3.14–6.84% with accuracy of 91.38–94.42% for aripiprazole. The method was successfully applied to human pharmacokinetic study of urapidil and aripiprazole in healthy human male volunteers. Copyright © 2013 John Wiley & Sons, Ltd.     

Development and validation of an LC‐ESI‐MS/MS method for the quantitation of hemslecin A in rhesus monkey plasma and its application in pharmacokinetics

In this study, a new LC‐ESI‐MS/MS‐based method was validated for the quantitation of hemslecin A in rhesus monkey plasma using otophylloside A as internal standard (IS). Hemslecin A and the IS were extracted from rhesus monkey plasma using liquid–liquid extraction as the sample clean‐up procedure, and were subjected to chromatography on a Phenomenex Luna CN column (150 × 2.0 mm, 3.0 µm) with the mobile phase consisting of methanol and 0.02 mol/mL ammonium acetate (55:45, v/v) at a flow rate of 0.2 mL/min. Detection was performed on an Agilent G6410B tandem mass spectrometer by positive ion electrospray ionization in multiple reaction monitoring mode, monitoring the transitions m/z 580.5 [M + NH₄]⁺ → 503.4 and m/z 518.2 [M + NH₄]⁺ → 345.0 for hemslecin A and IS, respectively. The assay was linear over the concentration range of 0.5–200 ng/mL and was successfully applied to a pharmacokinetic study in rhesus monkeys. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of cefuroxime lysine in rat brain microdialysates by ultra‐fast liquid chromatography with UV and tandem mass spectrometry: application to an acute toxicokinetic study

Cefuroxime lysine is a new second‐generation cephalosporins, which can penetrate the blood–brain barrier to cure the meningitis. In order to investigate its acute toxicokinetic study after intraperitoneal injection of 675 mg/kg cefuroxime lysine, a sensitive and clean ultra‐fast liquid chromatography–tandem mass spectrometry (UFLC‐MS/MS) method for the determination of cefuroxime lysine in microdialysate samples was developed and validated, which was compared with UFLC‐UV as a reference method. Chromatographic separation was performed on a Shim‐pack XR‐ODS C₁₈ column (75 × 3.0 mm, 2.2 µm), with an isocratic elution of 0.1% formic acid in acetonitrile–0.1% formic acid in water (45:55, v/v) for LC‐MS and acetonitrile–20 mm potassium dihydrogen phosphate (pH 3.0,20:80, v/v) for LC‐UV. The lower limit of detection was 0.01 µg/mL for LC‐MS and 0.1 µg/mL for LC‐UV method, with the same corresponding linearity range of 0.1–50 µg/mL. The intra‐ and inter‐day precisions (relative standard deviation) for both methods were from 1.1 to 8.9%, while the accuracy was all within ±10.9%. The results of both methods were finally compared using paired t‐test; the results indicated that the concentrations measured by the two methods correlated significantly (p < 0.05), which suggested that the two methods based on LC‐MS and LC‐UV were suitable for the acute toxicokinetic study. Copyright © 2014 John Wiley & Sons, Ltd.