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Endothelin receptor antagonists (ERAs) such as, ambrisentan, macitentan and sitaxentan are primarily used for the treatment of pulmonary arterial hypertension. Considering the rise in endothelin in pre-eclampsia, ERAs may also be useful in its treatment. To evaluate the pharmacokinetics of ERAs, a rapid ultra-performance liquid chromatography tandem mass spectrometry method was developed and validated to determine the concentration of ambrisentan, macitentan and sitaxentan in human plasma. Plasma samples were treated with methanol to induce protein precipitation. A chromatographic separation was performed on a C 18 column using a gradient of methanol-water containing 0.1% formic acid and 0.013% ammonium acetate and a flow rate of 0.5 ml/min. Multiple reaction monitoring was used for quantification. This method was validated in a linear range of 20.28-2028 μg/l for ambrisentan, 4.052-405.2 μg/l for macitentan and 205.4-10 270 μg/l for sitaxentan. The method was successfully validated according to US Food and Drug Administration guidelines to determine the concentrations of macitentan, ambrisentan and sitaxentan in human plasma. This method is now being used for study samples and clinical patient samples., (© 2019 John Wiley & Sons, Ltd.)

A novel ultra-high-pressure liquid chromatography-tandem mass spectrometry method was developed and validated for the determination of the dopamine receptor agonist rotigotine in human plasma. Following liquid-liquid extraction with tert-butyl methyl ether from 500 μL plasma, the chromatographic analysis was performed on a Gemini NX3 column using 5 mm pH 5.0 ammonium acetate-5 mm ammonium acetate in methanol as binary gradient mobile phase, at a flow rate of 0.3 mL/min. The MS/MS ion transitions were 316.00 → 147.00 for rotigotine and 256.10 → 211.00 for the internal standard (lamotrigine). The lower limit of quantitation was 50 pg/mL and the linearity was determined from 50 to 2500 pg/mL. The mean recovery was 96.9%. Both intra- and interassay imprecision and inaccuracy were ≤15% at all quality control concentrations. The method was successfully applied to measure morning trough plasma rotigotine concentrations in a series of patients with Parkinson's disease on chronic treatment. The present study describes the first fully validated method for rotigotine determination in human plasma., (Copyright © 2017 John Wiley & Sons, Ltd.)

A simple, sensitive and reproducible high-performance liquid chromatography (HPLC) assay method was developed for the estimation of 3-pentylbenzo[c]thiophen-1(3H)-one (S5 ), a potential anti-ischemic stroke agent, in dog plasma. The analytical procedure involves protein precipitation of S5 and nobiletin (internal standard) from dog plasma with acetonitrile. Chromatographic separation was achieved on Sapphire C18 analytical column with methanol-water (80:20, v/v) as mobile phase. The eluate was monitored using a UV detector set at 260 nm. The calibration curves were linear over the range of 0.2-20 µg/mL. Absolute recoveries of S5 were 79.2-86.1% from dog plasma. The intra- and inter-day relative standard deviation precisions were <7 and 5%, respectively. The method was successfully applied to the pharmacokinetic study of S5 in beagle dogs., (Copyright © 2014 John Wiley & Sons, Ltd.)

The major metabolite of duloxetine is a glucuronide conjugate of 4-hydroxy duloxetine (4-HD). However, interestingly, there have been no reports determining concentrations of 4-HD and no fully validated method has been established for measuring duloxetine and 4-HD in rat plasma. We developed a method for the simultaneous quantification of duloxetine and its metabolite in rat plasma using high-performance liquid chromatography tandem mass spectrometry. Duloxetine and 4-HD were analyzed on a reverse-phase C18 analytical column after protein precipitation of the plasma sample with methanol, using carbamazepine as an internal standard. The isocratic mobile phase of 5 mm ammonium acetate-methanol (4:6, v/v) was eluted at 0.4 mL/min. Quantification was performed on a triple-quadrupole mass spectrometer using electrospray ionization, and the ion transition monitored in selective reaction monitoring mode. The coefficient of variation for assay precision was <18.0%, and the accuracy was 84.0-118.0%. This method was successfully used to measure the concentrations of duloxetine and its metabolite in plasma following the oral administration of a single 40 mg/kg dose in rats., (Copyright © 2013 John Wiley & Sons, Ltd.)

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/concentration(2) ) 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 liquid chromatography-tandem mass spectrometric (LC/MS/MS) method was developed for the determination of a selective Na(+)/H(+) exchanger inhibitor 4-cyano(benzo[b]thiophene-2-carbonyl)guanidine (KR-33028) in rat plasma. KR-33028 and the internal standard, linezolid, were extracted from rat plasma with ethyl acetate at neutral pH. The analytes were separated on an XBridge C(18) column with a mixture of methanol-0.1% formic acid (35:65, v/v) as mobile phase and detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r = 0.9998) over the concentration range of 2.0-1000 ng/mL. The coefficients of variation of intra- and inter-assay were 1.3-6.8% and the relative error was 0.8-5.0%. The recoveries of KR-33028 and linezolid were 70.5 and 84.6%, respectively. The lower limit of quantification for KR-33028 was 2.0 ng/mL using 50 microL plasma sample. This method was successfully applied to the pharmacokinetic study of KR-33028 in rats., (Copyright (c) 2007 John Wiley & Sons, Ltd.)

A sensitive and specific analytical method has been developed for the determination of a new anxiolytic (CGS 19480A) in human plasma using high performance liquid chromatography (HPLC). The drug and internal standard (CGS 18102A), were extracted with hexane at pH 7. Separations were achieved by reversed phase chromatography on a Nucleosil 5 C18 column at a flow rate of 1.0 mL/min. The mobile phase consisted of acetonitrile: 0.01 M phosphate buffer (pH 7): methanol (51:35:14, v:v:v), where the final pH of the mobile phase was adjusted to 4.0 using 85% phosphoric acid. Plasma standard curves were linear from 5.0 to 500 ng/ml, with recovery of the drug being greater than 95% at all concentrations. The method was validated over a concentration range of 5.0 to 500 ng/mL with a limit of quantification of 5.0 ng/mL. The method was successfully applied to the analysis of clinical samples from a single-dose safety and tolerability study conducted in six healthy male volunteers.