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Isocorynoxeine (ICOR) is one of the bioactive oxindole alkaloids inUncariaspecies. This study presents the pharmacokinetics and mass balance of ICOR in rats after oral dose of 40.0 mg/kg and intravenous dose of 4.0 mg/kg through detection of ICOR and its in vivo metabolites, using an optimized LC-MS with recoveries ranged from 94 to 104%, accuracy varied from 96 to 103%, and relative standard deviation for assay being less than 5%. ICOR reached its Cmaxof 336.7 ng/mL in plasma 3 hr after oral dose. The phase I metabolites of ICOR, 11-hydroxyisocorynoxeine (M1), and 10-hydroxyisocorynoxeine (M2) were detected in rat heart, kidneys, urine, and feces; whereas, in rat liver and bile, M1, M2, along with phase II metabolites, 11-hydroxyisocorynoxeine 11-O-β-D-glucuronide, and 10-hydroxyisocorynoxeine 10-O-β-D-glucuronide were identified. ICOR (77.0%) was excreted into feces and urine after oral administration within 72 hr, 0.93% drained into bile in 8 hr, 17.9% biotransformed into M1 and M2 at a ratio ofca. 1:1, and 0.028% detected in main organs attmax, in which brain uptake index is 3.2 ng/g. This work affords a developed and validated LC-MS for simultaneous determination of ICOR and itsin vivometabolites with improved precision and accuracy. [ABSTRACT FROM PUBLISHER]

A liquid chromatography–electrospray ionization-time-of-flight/mass spectrometry (LC–ESI-TOF/MS) method was developed for the determination of 4-beta-hydroxycholesterol (4β-HC) in rat plasma, to evaluate cytochrome P450 3A (CYP3A) induction liability of a novel cyclin dependent kinases (CDKs) inhibitor, AGM-130. The method consisted of sample preparation without derivatization reagents for high sensitivity such as picolinyl ester, which could be labor-intensive and time consuming. The 4% bovine serum albumin in phosphate-buffered saline as a surrogate matrix was used in the calibration curve and quality control samples for the determination of 4β-HC. Stable isotope-labeled (SIL) 4β-HC (d7-4β-HC) was used as an internal standard. A quadratic regression (weighted 1/concentration), with an equation y = ax2 + bx + c, was used to fit calibration curves over the concentration range of 3.01–2220 ng/mL for 4β-HC. For quality control samples at 15.0, 165, and 1820 ng/mL from the qualification experiment, the within-run accuracy ranged from 95% to 105% with precision values ≤10% for 4β-HC. This novel LC–ESI-TOF/MS method was successfully applied to evaluate the potential of CYP3A induction by 5′-hydroxy-5-nitro-indirubin oxime (AGM-130) in rat. [ABSTRACT FROM AUTHOR]

□A rapid and sensitive analytical method of liquid chromatography combined with tandem mass spectrometry (LC–MS/MS) was established for simultaneous quantitative analysis of hydrazine, methylhydrazine, and 1,1-dimethylhydrazine in rat plasma. Plasma samples were pretreated with protein precipitation and optimized derivatization procedure. Separation was achieved using acetonitrile and water containing 5 mM ammonium acetate as gradient elution. The optimized mass transition ion-pairs (m/z) monitored for three hydrazine derivatives werem/z299.1→m/z151.1,m/z180.2→m/z78.1, andm/z194.2→m/z59.1, respectively. The lower limit of quantitation (LLOQ) of hydrazine was 1 ng/mL and those of other compounds were 10 ng/mL. Intra- and inter-day precision were within 14.00%. Meanwhile, the relative error was within the acceptable range. The recovery of three analytes and (IS) were between 57.78 ± 4.73%and 107.04 ± 7.46%.Target derivatives were stable under the conditions tested. The dilution test showed that this method is not only suitable for samples in the detection limit but also applicable for high concentration samples that exceed the upper limit of detection. The performance of the method was successfully verified for real rat plasmas and would be useful for routine analysis in cases of suspected hydrazine poisoning. [ABSTRACT FROM AUTHOR]

A sensitive and selective liquid chromatography mass spectrometry (LC–MS) method for determination of isocorynoxeine in rat plasma was developed. After addition of midazolam as internal standard (IS), sample preparation was performed by using liquid–liquid extraction with ethyl acetate. Chromatographic separation was achieved on a Zorbax SB-C18 (2.1 mm × 150 mm, 5 µm) column with acetonitrile-0.1% formic acid as mobile phase with gradient elution. Electrospray ionization (ESI) source was applied and operated in positive ion mode; selective ion monitoring (SIM) mode was used to quantify using target fragment ionsm/z383 for isocorynoxeine andm/z326 for the IS. Calibration plots were linear over the range of 5–500 ng/mL for isocorynoxeine in plasma. Lower limit of quantification (LLOQ) for isocorynoxeine was 5 ng/mL. Mean recovery of isocorynoxeine from plasma was in the range of 93.6–96.6%. CV of intra-day and inter-day precision were both less than 15%. The newly developed method is simple, sensitive, and could function effectively in pharmacokinetic characterization of isocorynoxeine in rat plasma. [ABSTRACT FROM PUBLISHER]

A sensitive and simple liquid chromatography/electrospray mass spectrometry (LC-ESI-MS) method for determination of diphenoxylate in rat plasma using one-step protein precipitation was developed and validated. After addition of estazolam as internal standard (IS), protein precipitation by acetonitrile was used as sample preparation. Chromatographically separation was achieved on an SB-C18 (2.1 mm × 50 mm, 3.5 µm) column with acetonitrile-0.1% formic acid as the mobile phase with gradient elution. Electrospray ionization (ESI) source was applied and operated in positive ion mode; selected ion monitoring (SIM) mode was used to quantification using target fragment ionsm/z453.1 for diphenoxylate andm/z294.8 for the IS. Calibration plots were linear over the range of 5–1000 ng/mL for diphenoxylate in rat plasma. Lower limit of quantification (LLOQ) for diphenoxylate was 5 ng/mL. Mean recovery of diphenoxylate from plasma was in the range of 96.69–98.27%. RSD of intra-day and inter-day precision were both less than 9%. This method is simple and sensitive enough to be used in pharmacokinetic research for determination of diphenoxylate in rat plasma. [ABSTRACT FROM AUTHOR]

A highly selective and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the quantification of scicinib, a novel thiosemicarbazone analogue and anticancer agent in rat plasma. Protein precipitation with saturated EDTA solution and methanol was selected for sample preparation, and brodimoprim was employed as the internal standard (IS). The analytes were separated on a Symmetry C18column (200 × 4.6 mm i.d., 5 µm) by isocratic elution with a mobile phase consisting of methanol and 0.2 mM EDTA (75:25, v/v) at a flow rate of 0.4 mL/min. After electrospray ionization, the analyte and IS were recorded under selected reaction monitoring (SRM) mode. The chosen transition wasm/z313.0 → 267.9 for scicinib andm/z339.0 → 280.9 for IS, respectively. The validated linearity range is 5–5000 ng/mL, with the lower limit of quantitation of 5 ng/mL. The developed method was successfully applied to a pharmacokinetic study of scicinib in rats after a single intravenous administration of 5 mg/kg. [ABSTRACT FROM AUTHOR]

A simple and rapid liquid chromatography-tandem mass spectrometry (LC–MS/MS) method has been developed and validated for the quantitation of indirubin-5-nitro-3′-monoxime (5-NIO) in rat plasma using 5-chloro-5′-chloro-indirubinoxime as the internal standard. The sample preparation involved protein precipitation using acetonitrile. Separation was achieved on an Xterra column C18 (2.1 mm × 50 mm, i.d. 5 µm) using a mixture of 0.1% formic acid-water/acetonitrile (18:82, v/v) as the mobile phase at a flow rate of 300 µL/min. Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization and multiple reaction monitoring (MRM) in negative ion mode. The total chromatographic run time was 2.5 min, and the calibration curves of 5-NIO were linear (correlation coefficient range: 0.9989–0.9999) over the concentration range of 0.2–2000 ng/mL in rat plasma. Also, the detection limit of the method was 0.05 ng/mL and it showed good accuracy and precision within the concentration range of 0.45–376 ng/mL. This validated method was successfully applied to estimating the pharmacokinetic parameters of 5-NIO following intravenous administration of 5-NIO to rats. [ABSTRACT FROM AUTHOR]

A simple and specific LC-MS/MS method for the determination of FK506 in blood was developed, validated, and successfully applied in pharmacokinetic studies of the effect of silymarin on FK506 in rats. Blood samples were extracted by liquid-liguid extraction with methyl tert-butyl ether and separated on an Eclipse plus-C18 column (150 × 2.1 mm, 3.5 µm) with the mobile phase of acetonitrile-10 mM ammonium acetate buffer solution (80:20, v/v). FK506 was detected without interference in the multiple-reaction monitoring mode with positive electrospray ionization. Good linearity was achieved over a range of 2.0–200 ng mL−1. The intra- and inter-day precisions were less than 13.5 % for all concentrations of quality control samples. The recoveries of FK506 were 74.2–85.3 %. Although the mean Cmax and AUC0 − ∞ of FK506 were increased to some extent, there was no significant difference in the pharmacokinetic profile of FK506 after oral administration to rats in the presence and absence of silymarin (200 mg kg−1, 2 times/d for 14 d). [ABSTRACT FROM AUTHOR]

To evaluate the bioavailability of exemestane (EXM) from self-micro emulsifying drug delivery systems (SMEDDS) and suspension formulations, a sensitive, specific, and rapid liquid chromatography-mass spectrometric method was developed and validated. The analyte was extracted from plasma samples and detected by mass spectrometry (MS) with an atmospheric pressure positive-ion chemical ionization (APCI) mode using a heated nebulizer interface. Progesterone (PGS) was used as the internal standard. A Hychrome RPB-L428 column was used to perform the chromatographic separation, the mobile phase being methanol and 15 mM ammonium formate (80:20). The MS detection used a heated nebulizer interface, with multiple reaction monitoring (MRM) operated in positive-ion mode. Both, EXM and PGS were well-separated and identified by their relative retention times, that is, 1.13 and 1.84 min, respectively. After oral administration of EXM loaded SMEDDS and suspension formulation to rats, a significant difference was observed in the pharmacokinetic behavior of drug in both the formulations, and a 2.9-fold increase in the relative bioavailability of EXM was observed with the SMEDDS as compared with suspension formulation. The developed method was found to be suitable for bioanalysis of exemestane and, hence, successfully depicted the bioavailability enhancement of exemestane SMEDDS in Wistar rats. [ABSTRACT FROM AUTHOR]

A sensitive and selective liquid chromatography-mass spectrometry (LC-MS) method for determination of tolbutamide and its metabolite hydroxytolbutamide in rat plasma was developed and validated. The analytes and internal standard omeprazole were extracted from plasma by liquid-liquid extraction using ethyl acetate, and chromatographically separated on a Zorbax SB-C18 column (2.1 mm × 50 mm, 3.5 µm) using acetonitrile-0.1% formic acid as the mobile phase with gradient elution. Electrospray ionization (ESI) source was applied and operated in positive ion mode, and selected ion monitoring (SIM) mode used to quantify tolbutamide and its metabolite hydroxytolbutamide. The assay was linear over the range 10–20000 ng/mL for tolbutamide and 5–800 ng/mL for hydroxytolbutamide, with a lower limit of quantification (LLOQ) of 10 ng/mL for tolbutamide and 5 ng/mL for hydroxytolbutamide. Intra- and inter-day precision were less than 12% and the accuracy were in the range 88.8–109.7%. This developed method was successfully used for determination of tolbutamide and metabolite hydroxytolbutamide in rat plasma for pharmacokinetic study. [ABSTRACT FROM AUTHOR]