Determination of piracetam in rat plasma by LC–MS/MS and its application to pharmacokinetics

A sensitive and selective liquid chromatography–tandem mass spectrometry method for the determination of piracetam in rat plasma was developed and validated over the concentration range of 0.1–20 µg/mL. After addition of oxiracetam as internal standard, a simplified protein precipitation with trichloroacetic acid (5%) was employed for the sample preparation. Chromatographic separation was performed by a Zorbax SB‐Aq column (150 × 2.1 mm, 3.5 µm). The mobile phase was acetonitrile–1% formic acid in water (10:90 v/v) delivered at a flow rate of 0.3 mL/min. The MS data acquisition was accomplished in multiple reaction monitoring mode with a positive electrospray ionization interface. The lower limit of quantification was 0.1 µg/mL. For inter‐day and intra‐day tests, the precision (RSD) for the entire validation was less than 9%, and the accuracy was within the 94.6–103.2% range. The developed method was successfully applied to pharmacokinetic studies of piracetam in rats following single oral administration dose of 50 mg/kg. Copyright © 2010 John Wiley & Sons, Ltd.     

Rapid determination and comparative pharmacokinetics of tetrahydropalmatine in spontaneously hypertensive rats and normotensive rats

A rapid high‐performance liquid chromatographic method was developed and validated for determination of tetrahydropalmatine (THP), an active component of Rhizoma Corydalis, in rat plasma. The samples were prepared using protein precipitation and separated on an Agilent XDB‐C₁₈ column (150 × 4.6 mm, 5 µm) with the mobile phase consisting of methanol–0.1% phosphate acid solution, adjusted with triethylamine to pH 5.5 (65:35). Good linearity was found within 0.10–10.00 µg/mL of THP in rat plasma sample. The intra‐ and inter‐day precision values were less than 10%. The developed method was successfully applied to assess the pharmacokinetics of THP in spontaneously hypertensive rats (SHR) and normotensive rats. After oral administration of a single dose of THP (60 mg/kg), the maximum plasma concentrations were 6.15 ± 2.1 and 7.54 ± 2.9 µg/mL for normotensive rats and SHR, respectively. The mean values of AUC_0–∞ of THP in SHR were 81.44 ± 45.0 µg h/mL, significantly higher (p < 0.05) than in normotensive rats (44.06 ± 19.6 µg h/mL). The t_1/2 and MRT in SHR were much longer than that in healthy Sprague–Dawley rats, indicating slow elimination of THP in SHR. The results indicated that there are some differences in pharmacokinetics of THP in SHR and Sprague–Dawley rats and it is very important to investigate the pharmacokinetic properties of drugs in pathological conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

UHPLC‐MS method for determination of gambogic acid and application to bioavailability,pharmacokinetics, excretion and tissue distribution in rats

A sensitive ultrahigh performance liquid chromatography tandem mass spectrometry (UHPLC‐MS) method was developed for determination of gambogic acid (GA) in rat plasma, urine, bile and main tissues. GA was separated on an Agilent Zorbax XDB–C₁₈ column (50 × 2.1 mm, 1.8 µm) with gradient mobile phase at the flow rate of 0.2 mL/min. The detection was performed by negative electrospray ionization with multiple reaction monitoring mode. The calibration curves of GA were linear between 1.0 and 1000 ng/mL in rat plasma and bile and between 1.0 and 500 ng/mL in urine and tissues. The lowest limit of quantification for all matrices was 1.0 ng/mL. Both accuracy and precision of the assay were satisfactory. This validated method was firstly applied to bioavailability (BA), pharmacokinetics, excretion and tissue distribution in rats. The BAs of GA (40 and 80 mg/kg) in rats were 0.25 and 0.32%, respectively. GA was distributed extensively in rats after oral administration and exhibited the highest level in liver. GA reached the cumulative excretion amount of 25.3 ± 1.7 µg in bile and 0.275 ± 0.08 µg in urine after i.g. 80 mg/kg to rats at 24 h. The present results would be helpful for further clinical use of GA as a potential anticancer drug. Copyright © 2015 John Wiley & Sons, Ltd.     

Development and validation of an LC‐MS/MS method for simultaneous quantification of levodopa and MD01 in rat plasma and its application to a pharmacokinetic study of mucuna pruriens extract

Mucuna pruriens, an ancient Indian herbal medicine containing levodopa, is widely used for Parkinson's disease. In order to simultaneously determine levodopa and 1,1‐dimethyl‐3‐carboxy‐6,7‐dihydroxy‐1,2,3,4‐tetrahydroisoquinoline (MD01) in rat plasma, an improved LC‐MS/MS method was developed and validated for a pharmacokinetic study in rats orally administered levodopa or Mucuna pruriens extract (MPE). Elimination of matrix effect and improvement of extraction recovery were achieved through systematic optimization of reversed‐phase and hydrophilic interaction chromatographic conditions together with sample clean‐up procedures. A satisfactory chromatographic performance was obtained with a Thermo Aquasil C₁₈ column (50 × 2.1 mm, 3 µm) using acetonitrile and water containing 0.2% formic acid as mobile phases. Futhermore, sodium metabisulfite and formic acid were used as stabilizers in neat solutions as well as rat plasma. The method was validated in a dynamic range of 20.0–10,000 ng/mL for levodopa and MD01; the intra‐ and inter‐day precision and accuracy were acceptable. The method was successfully utilized to determine the levodopa level in plasma samples of rats administered levodopa or MPE. Pharmacokinetic results showed that an increase in the AUC of levodopa was observed in rats following oral administration of multiple doses of MPE. Copyright © 2016 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.     

Pharmacokinetics of aconitine in rat skin after oral and transdermal gel administrations

The purpose of this study was to evaluate percutaneous penetration and arrhythmogenic effects of aconitine after transdermal administration, compared with the oral route. Skin penetration of aconitine was tested by a microdialysis technique in rats and in vivo recovery was determined by retrodialysis. After oral and transdermal administration of aconitine, dialysate was sampled at 20 min intervals until the end of the experiment for the determination of concentration of aconitine in skin. Blood samples were collected and analyzed using a validated HPLC‐MS/MS method. In addition, we concurrently recorded the electrocardiogram (ECG). The in vivo recovery of aconitine in the skin was calculated to be 39.59%. The C_max values for aconitine absorbed into the skin after oral and transdermal administration were 1.51 ± 0.53 and 2723.8 ± 848.8 ng/mL, respectively, and within the plasma, 215.86 ± 79.29 and 20.92 ± 3.15 ng/mL. The C_max value for the plasma concentration of aconitine after oral administration was approximately 10 times higher than with the transdermal route. For oral administration, the ECG revealed various types of arrhythmias at a period of T_max, which is normal in transdermal gel administration. These results indicate that transdermal aconitine gel is a safe formulation that can deliver the drug in sufficient amounts and safe concentrations to produce therapeutic action in rats. Copyright © 2011 John Wiley & Sons, Ltd.     

Simultaneous determination of senkyunolide I and senkyunolide H in rat plasma by LC‐MS: application to a comparative pharmacokinetic study in normal and migrainous rats after oral administration of Chuanxiong Rhizoma extract

A selective liquid chromatographic–mass spectrometric method has been developed and validated for simultaneous determination of senkyunolide I (SEI) and senkyunolide H (SEH) from Chuanxiong Rhizoma in rat plasma. Plasma samples were extracted by liquid–liquid extraction with ethyl acetate and separated on a Kromasil C₁₈ column (250 × 4.6 mm, 5 µm), with methanol–water (55:45, v/v) as mobile phase. The linear range was 0.05–25 µg/mL for SEI and 0.01–5.0 µg/mL for SEH, with lower limits of quantitation of 0.05 and 0.01 µg/mL, respectively. Intra‐ and inter‐day precision were within 10.0 and 9.8%, and the accuracies (relative errors) were <9.6 and 5.9%, with the mean extraction recoveries 81.0–86.6 and 80.5–85.0% for the two anayltes, respectively. The validated method was successfully applied to a comparative pharmacokinetic study of SEI and SEH in normal and migrainous rats after oral administration of Chuanxiong Rhizoma extract. The results indicated that there were obvious differences between normal and migrainous rats in the pharmacokinetic behavior after oral administration of Chuanxiong Rhizoma extract. The absorption of SEI and SEH were significantly increased in migrainous rats compared with normal rats. Copyright © 2015 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.     

Tissue distribution and metabolism of the putative cancer chemopreventive agent 3′,4′,5′‐trimethoxyflavonol (TMFol) in mice

3′,4′,5′‐Trimethoxyflavonol (TMFol) is a synthetic flavonol with preclinical cancer chemopreventive properties. The hypothesis was tested that, in mice, p.o. administration of TMFol results in measureable levels of the parent in target tissues. A single oral dose (240 mg/kg) was administered to mice (n = 4 per time point) with time points ranging from 5 to 1440 min. TMFol and its metabolites were identified and quantitated in all tissues by high‐performance liquid chromatography (HPLC). Plasma levels of TMFol were at the limit of quantification or below, although metabolites were identified. Peak levels of TMFol in the gastrointestinal tract and the prostate averaged 1671 ± 265 µg/g (5.3 µmol/g) and 6.0 ± 1.6 µg/g (18.4 nmol/g), and occurred 20 and 360 min post‐dose, respectively. The area under the tissue concentration–time curve (AUC) for TMFol was greater than those of the metabolites, indicating that TMFol is relatively metabolically stable. Micromolar TMFol levels are easily achieved in the prostate and gastrointestinal tract, suggesting that TMFol might exert chemopreventive efficacy at these tissue sites. Further investigations are warranted to elucidate the potential chemopreventive potency of TMFol. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of Pithecellobium jiringa ethanol extract against ethanol-induced gastric mucosal injuries in Sprague-Dawley rats

Current anti-gastric ulcer agents have side effects, despite the progression and expansion of advances in treatment. This study aimed to investigate the gastroprotective mechanisms of Pithecellobium jiringa ethanol extract against ethanol-induced gastric mucosal ulcers in rats. For this purpose, Sprague Dawley rats were randomly divided into five groups: Group 1 (normal control) rats were orally administered with vehicle (carboxymethyl cellulose), Group 2 (ulcer control) rats were also orally administered with vehicle. Group 3 (positive control) rats were orally administered with 20 mg/kg omeprazole, Groups 4 and 5 (experimental groups) received ethanol extract of Pithecellobium jiringa ethanol extract at a concentration of 250 and 500 mg/kg, respectively. Sixty minutes later, vehicle was given orally to the normal control group, and absolute ethanol was given orally to the ulcer control, positive control and experimental groups to generate gastric mucosal injury. The rats were sacrificed an hour later. The effect of oral administration of plant extract on ethanol-induced gastric mucosal injury was studied grossly and histology. The level of lipid peroxidation (malondialdehyde-MDA), superoxide dismutase (SOD) and gastric wall mucus were measured from gastric mucosal homogenate. The ulcer control group exhibited severe gastric mucosal injury, and this finding was also confirmed by histology of gastric mucosa which showed severe damage to the gastric mucosa with edema and leucocyte infiltration of the submucosal layer. Pre-treatment with plant extract significantly reduced the formation of ethanol-induced gastric lesions, and gastric wall mucus was significantly preserved. The study also indicated a significant increase in SOD activity in gastric mucosal homogenate, whereas a significant decrease in MDA was observed. Acute toxicity tests did not show any signs of toxicity and mortality up to 5 g/kg. The ulcer protective effect of this plant may possibly be due to its preservation of gastric wall mucus along with increased SOD activity and reduction of oxidative stress (MDA). The extract is non-toxic, even at relatively high concentrations.     

A rapid and simple RP‐HPLC method for quantification of kirenol in rat plasma after oral administration and its application to pharmacokinetic study

A rapid and simple reverse‐phase high‐performance liquid chromatography (RP‐HPLC) was developed and validated for the quantification of kirenol in rat plasma after oral administration. Kirenol and darutoside (internal standard, IS) were extracted from rat plasma using Cleanert™ C₁₈ solid‐phase extraction (SPE) cartridge. Analysis of the extraction was performed on a Thermo ODS‐2 Hypersil C₁₈ reversed‐phase column with a gradient eluent composed of acetonitrile and 0.1% phosphoric acid. The flow rate was 1.0 mL/min and the detection wavelength was set at 215 nm. The calibration curve was linear over the range of 9.756–133.333 µg/mL (r² = 0.9991) in rat plasma. The lower limits of detection and quantification were 2.857 and 9.756 µg/mL, respectively. The intra‐ and inter‐day precisions (relative standard deviation, RSD) were between 2.24 and 4.46%, with accuracies ranging from 91.80 to 102.74%. The extraction recovery ranged from 98.16 to 107.62% with RSD less than 4.81%. Stability studies showed that kirenol was stable in preparation and analytical process. The present method was successfully applied to the pharmacokinetic study of kirenol in male Sprague–Dawley rats after oral administration at a dose of 50 mg/kg. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of a liquid chromatography–tandem mass spectrometry method for the determination of Grayanotoxins in rat blood and its application to toxicokinetic study

A sensitive and specific high‐performance liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed for the determination of Grayanotoxin I (GTX I) and Grayanotoxin III (GTX III) in rat whole blood. Grayanotoxins (GTXs) and clindamycin as internal standard (IS) were extracted from rat blood via solid‐phase extraction using PEP solid‐phase extraction cartridges. Chromatographic separation of the analytes was achieved on a Kinetex C₁₈ (100 × 2.1 mm, 2.6 µm) reversed‐phase column using a gradient elution with the mobile phase of 1% acetic acid in water and methanol at a flow rate of 0.2 mL/min. Electrospray ionization mass spectrometry was operated in the positive ion mode with multiple reaction monitoring. The calibration curves obtained were linear over the concentration range of 1–100 ng/mL with a lower limit of quantification of 1 ng/mL for GTXs. The relative standard deviation of intra‐day and inter‐day precision was below 6.8% and accuracy ranged from 94.8 to 106.6%. The analytes were stable in the stability studies. The validated method was successfully applied to the quantification and toxicokinetic study of GTXs in rats for the first time after oral administration of 11.52 mg/kg mad honey and 0.35 mg/kg GTX III, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

An LC‐MS/MS method for determination of curculigoside with anti‐osteoporotic activity in rat plasma and application to a pharmacokinetic study

A rapid, simple, selective and sensitive LC‐MS/MS method was developed for the determination of curculigoside in rat plasma. The analytical procedure involves extraction of curculigoside and syringin (internal standard, IS) from rat plasma with a one‐step extraction method by protein precipitation. The chromatographic resolution was performed on an Agilent XDB‐C₁₈ column (4.6 × 50 mm, 5 µm) using an isocratic mobile phase of methanol with 0.1% formic acid and H₂O with 0.1% formic acid (45:55, v/v) at a flow rate of 0.35 mL/min with a total run time of 2.0 min. The assay was achieved under the multiple‐reaction monitoring mode using positive electrospray ionization. Method validation was performed according to US Food and Drug Administration guidelines and the results met the acceptance criteria. The calibration curve was linear over 4.00–4000 ng/mL (R = 0.9984) for curculigoside with a lower limit of quantification of 4.00 ng/mL in rat plasma. The intra‐ and inter‐day precisions and accuracies were 3.5–4.6 and 0.7–9.1%, in rat plasma, respectively. The validated LC‐MS/MS method was successfully applied to a pharmacokinetic study of curculigoside in rats after a single intravenous and oral administration of 3.2 and 32 mg/kg. The absolute bioavailability of curculigoside after oral administration was 1.27%. Copyright © 2013 John Wiley & Sons, Ltd.     

Metabolic profiling study on potential toxicity and immunotoxicity‐biomarker discovery in rats treated with cyclophosphamide using HPLC‐ESI‐IT‐TOF‐MS

Despite the recent advances in understanding toxicity mechanism of cyclophosphamide (CTX), the development of biomarkers is still essential. CTX‐induced immunotoxicity in rats by a metabonomics approach was investigated using high‐performance liquid chromatography coupled with ion trap time‐of‐flight mass spectrometry (HPLC‐ESI‐IT‐TOF‐MS). The rats were orally administered CTX (30 mg/kg/day) for five consecutive days, and on the fifth day samples of urine, thymus and spleen were collected and analyzed. A significant difference in metabolic profiling was observed between the CTX‐treated group and the control group by partial least squares‐discriminant analysis (PLS‐DA), which indicated that metabolic disturbances of immunotoxicity in CTX‐treated rats had occurred. One potential biomarker in spleen, three in urine and three in thymus were identified. It is suggested that the CTX‐toxicity mechanism may involve the modulation of tryptophan metabolism, phospholipid metabolism and energy metabolism. This research can help to elucidate the CTX‐influenced pathways at a low dose and can further help to indicate the patients' pathological status at earlier stages of toxicological progression after drug administration. Copyright © 2014 John Wiley & Sons, Ltd.     

LC‐MS/MS determination of pogostone in rat plasma and its application in pharmacokinetic studies

Pogostone is an important constituent of Pogostemon cablin (Blanco) Benth., and possesses various known bioactivities. A rapid, simple and sensitive liquid chromatography tandem mass spectrometry (LC‐MS/MS) method was developed for the analysis of pogostone in rat plasma using chrysophanol as internal standard (IS). The analytes were extracted with methanol and separated using a reversed‐phase YMC‐UltraHT Pro C₁₈ column. Elution was achieved with a mobile phase consisting of methanol–water (75:25, v/v) for 5 min at a flow rate of 400 μL/min. The precursor/product transitions (m/z) under MS/MS detection with negative electrospray ionization (ESI) were 223.0 → 139.0 and 253.1 → 224.9 for pogostone and IS, respectively. The calibration curve was linear over the concentration range 0.05–160 µg/mL (r = 0.9996). The intra‐ and inter‐day accuracy and precision were within ±10%. The validated method was successfully applied to the preclinical pharmacokinetic investigation of pogostone in rats after intravenous (5, 10 and 20 mg/kg) and oral administration (5, 10 and 20 mg/kg). Finally, the oral absolute bioavailability of pogostone in rats was calculated to be 70.39, 78.18 and 83.99% for 5, 10 and 20 mg/kg, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Development of a validated UPLC–MS/MS method for determination of humantenmine in rat plasma and its application in pharmacokinetics and bioavailability studies

Humantenmine (HMT), the most toxic compound isolated from Gelsemium elegans Benth , is a well‐known active herbal compound. A rapid and sensitive ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method was developed and validated to estimate the absolute oral bioavailability of HMT in rats. Quantification was performed by multiple reaction monitoring using electrospray ionization operated in positive ion mode with transitions of m/z 327.14 → m/z 296.19 for HMT and m/z 323.20 → m/z 236.23 for gelsemine (internal standard, IS). The linear range of the calibration curve was 1–256 nmol/L, with a lower limit of quantification at 1 nmol/L. The accuracy of HMT ranged from 89.39 to 107.5%, and the precision was within 12.24% (RSD). Excellent recovery and negligible matrix effect were observed. HMT remained stable during storage, preparation and analytical procedures. The pharmacokinetics of HMT in rats showed that HMT reached the concentration peak at 12.50 ± 2.74 min with a peak concentration of 28.49 ± 6.65 nmol/L, and the corresponding area under the concentration–time curve (AUC_0–t ) was 1142.42 ± 202.92 nmol/L min after 200 μg/kg HMT was orally administered to rats. The AUC_0–t of HMT given at 20 μg/kg by tail vein administration was 1518.46 ± 192.24 nmol/L min. The calculated absolute bioavailability of HMT was 7.66%.     

LC‐MS/MS determination of bakkenolide D in rats plasma and its application in pharmacokinetic studies

A sensitive and rapid liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed and validated for determination of bakkenolide D (BD), which was further applied to assess the pharmacokinetics of BD. In the LC‐MS/MS method, the multiple reaction monitoring mode was used and columbianadin was chosen as internal standard. The method was validated over the range of 1–800 ng/mL with a determination coefficient >0.999. The lower limit of quantification was 1 ng/mL in plasma. The intra‐ and inter‐day accuracies for BD were 91–113 and 100–104%, respectively, and the inter‐day precision was <15%. After a single oral dose of 10 mg/kg of BD, the mean peak plasma concentration of BD was 10.1 ± 9.8 ng/mL at 2 h. The area under the plasma concentration–time curve (AUC_{0–24 h}) was 72.1 ± 8.59 h ng/mL, and the elimination half‐life (T_1/2) was 11.8 ± 1.9 h. In case of intravenous administration of BD at a dosage of 1 mg/kg, the AUC_{0–24 h} was 281 ± 98.4 h?ng/mL, and the T_1/2 was 8.79 ± 0.63 h. Based on these results, the oral bioavailability of BD in rats at 10 mg/kg is 2.57%. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of toosendanin in rat plasma by ultra‐performance liquid chromatography–electrospray ionization–mass spectrometry and its application in a pharmacokinetic study

Toosendanin (TSN) is a major triterpenoid existing in Melia toosendan, which has been used as a digestive tract parasiticide and insecticide but with serious hepatotoxicity. An ultra‐performance liquid chromatography–electrospray ionization–mass spectrometry method was developed for determination of TSN in rat plasma. Plasma samples were separated on Acquity UPLC^TM BEH C₁₈ column with acetonitrile and water as flow phase by gradient elution and determined by quadrupole mass spectrometer in negative selective ion monitoring mode. Usolic acid was used as internal standard. The calibration curves were linear over 0.02–3.0 µg/mL for TSN with a lower limit of quantification (LLOQ) of 20 ng/mL in rat plasma. The extraction recoveries of TSN were within 74.3–80.7% with an accuracy of 94.5–108.9%. The intra‐ and inter‐day precision values of the assay at three quality control levels were 8.8–13.8% and <13.9% at LLOQ level, respectively. The method was successfully applied to a pharmacokinetic study of TSN in rats after a single intravenous and oral administration of 2 and 60 mg/kg. The shorter T_max, higher V_d and Cl of TSN after oral administration indicated that TSN could be absorbed, distributed and eliminated quickly in rats in vivo. The absolute bioavailability of TSN after oral administration was 9.9%. Copyright © 2012 John Wiley & Sons, Ltd.     

Development and validation of a high‐performance liquid chromatographic method for the determination of stemoninine in rat plasma after administration of Stemona tuberosa extracts

For the first time, an HPLC method was developed and validated for the determination of stemoninine in plasma after oral and intravenous administration of the extract of the roots of Stemona tuberosa to rats. Plasma samples were analyzed on a Waters reversed‐phase C₁₈ column using a gradient mobile‐phase of eluent A (water containing 0.1% formic acid and 0.2% triethylamine, pH 3.68) and eluent B (acetonitrile–water, 50:50, v/v). The flow rate was 1.0 mL/min and the detector wavelength was 210 nm. The Waters Oasis solid‐phase extraction cartridge was applied for the preparation of plasma samples with high recovery. A good linear relationship was obtained in the concentration range of 1.55–124 µg/mL (r = 0.9995). The limits of quantification and detection were 1.55 and 0.42 µg/mL, respectively. The average recoveries ranged from 91.11 to 96.43% in plasma at stemoninine concentrations of 3.10, 62.0 and 99.2 µg/mL. Intra‐ and inter‐batch coefficient of variations were 3.27–5.37% and 2.49–3.92%, respectively. This method was successfully applied to pharmacokinetic studies after oral and intravenous administration of Stemona tuberosa extract in rats. Copyright © 2010 John Wiley & Sons, Ltd.     

An LC-MS/MS method for simultaneous determination of vincristine and verapamil in rat plasma after oral administration of a dual agent formulation

A rapid and sensitive method for simultaneous determination of vincristine and verapamil in rat plasma was first developed and validated, using high‐performance liquid chromatography–tandem mass spectrometry (LC‐MS/MS) in multiple reaction monitoring (MRM) mode via electrospray ionization (ESI). The method, which required a small sample volume (25 µL) of plasma, was linear in the concentration range of 0.5–500 ng/mL for vincristine and 0.1–100.0 ng/mL for verapamil. Finally, the method was successfully employed in a pharmacokinetic study of vincristine and verapamil in rats after an oral administration of a dual‐agent formulation containing vincristine and verapamil. Copyright © 2010 John Wiley & Sons, Ltd.