Simultaneous determination of ginsenosides and bufadienolides in rat plasma after the oral administration of Shexiang Baoxin Pill for pharmacokinetic study by liquid chromatography tandem mass spectrometry following solid‐phase extraction

A sensitive and reliable bioanalytical method was established for quantitati\ve and pharmacokinetic investigation of nine ginsenosides and seven bufadienolides in rat plasma after the oral administration of Shexiang Baoxin Pill by liquid chromatography–electrospray ionization tandem mass spectrometry, using tinidazole and digoxin as internal standards (ISTDs). All of the analytes and ISTDs obtained satisfactory recoveries by solid‐phase extraction using an Oasis HLB μElution Plate, which was eluted with methanol and ethyl acetate successively, and chromatographic separation was achieved on a Shim‐pack XR‐ODSIIcolumn (75 × 2.0 mm, 2.2 μm) with gradient elution using a mixture of acetonitrile–0.1% formic acid solution (v /v) as the mobile phase at a flow rate of 0.3 mL/min. Detection was carried out by a triple‐quadrupole tandem mass spectrometry with positive/negative ion switching multiple reaction monitoring mode. All analytes showed good linearity over a wide concentration range (r ² > 0.99). The lower limit of quantification was in the range 0.625–12.5 ng/mL for bufadienolides and 2–5.5 ng/mL for ginsenosides, and the mean recoveries of all analytes were in the range 78.29–99.35%. The intra‐ and inter‐day precisions (RSD) were in the range 0.08–12.38% with the accuracies between 86.09 and 99.40%. The validated method was then successfully applied to pharmacokinetic study of the above 16 compounds in rat plasma. Pharmacokinetic results indicated that the developed extraction and analytical method could be employed as a rapid, effective technique for pharmacokinetic study of multiple components, especially various polarity that are difficult to extract simultaneously.     

Pharmacokinetic study of five ginsenosides using a sensitive and rapid liquid chromatography–tandem mass spectrometry method following single and multiple oral administration of Shexiang Baoxin pills to rats

Shexiang Baoxin pills (SBP) are a traditional Chinese medicine that are used for treating coronary heart disease. Ginsenosides are the main effective components of SBP, but a comprehensive and deep pharmacokinetic study of ginsenosides in SBP, including multiple dosing and linear or nonlinear properties, is lacking. This study was designed to investigate and compare the pharmacokinetic characteristics of ginsenosides in SBP at a single dose and in multiple doses. A liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed for the simultaneous determination of the ginsenosides Rg1, Re, Rb3, Rc and Rb1 in rat plasma. Rats were randomly assigned to receive a single dose of 4, 8 or 12 g/kg and multiple doses (4 g/kg) of SBP for 8, 15 or 22 consecutive days. The results revealed that ginsenosides, following a single oral dose of 4 or 8 g/kg, were absorbed rapidly, with a T_max ranging from 0.250 to 1.08 h. The AUC_0–t and C_max of the ppd‐type ginsenosides Rb3, Rc and Rb1 were greater than those of the ppt‐type ginsenosides Rg1 and Re. Nondose‐dependent exposure was observed at doses of 4–12 g/kg for all of the ginsenosides. After multiple dosing, the plasma levels of the ppt‐type ginsenosides decreased, whereas those of the ppd‐type ginsenosides did not change significantly. In conclusion, the LC‐MS/MS method was successfully applied to investigate the pharmacokinetics of ginsenosides after single and multiple oral administrations of SBP. The ginsenosides did not accumulate after multiple dosing. The ppd‐type ginsenosides displayed more favorable pharmacokinetic properties compared with the ppt‐type ginsenosides. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of the constituents in rat plasma after oral administration of Shexiang Baoxin pill by HPLC‐ESI‐MS/MS

A valid method using liquid chromatography coupled with electrospray ionization (ESI) and ion trap mass spectrometry was established for the study of the absorbed components in rat plasma after oral administration of a traditional Chinese medicine (TCM) Shexiang Baoxin pill. The plasma was deproteinated by adding methanol prior to liquid chromatography, in which separation was carried out on a Symmetry C₁₈ column (5 µm, 250 × 4.6 mm). A linear gradient with 0.5% formic acid–water–acetonitrile was used as mobile phase. Mass spectra were acquired in both negative and positive modes. Twenty‐one components including 17 components from Shexiang Baoxin pill and four metabolites were observed from a comprehensive analysis of the chromatography of Shexiang Baoxin pill, controlled plasma and dosed plasma. All of the 17 prototype compounds and three of the metabolites were identified by comparing their retention behaviors and MS and MS/MS spectra with reference compounds and literature data. This study developed an integrated method for screening the bioactive constituents in plasma after oral adminstration of Chinese herbal medicine and provided helpful chemical information for further pharmacology and active mechanism research on TCM. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitation of acotiamide in rat plasma by UHPLC‐Q‐TOF‐MS: method development,validation and application to pharmacokinetics

A novel, sensitive and selective ultra‐high‐performance liquid chromatography–electrospray ionization mass spectrometry method was developed and validated for the quantification of acotiamide (ACT), a first‐in‐class drug used in functional dyspepsia, in rat plasma. A simple protein precipitation method with acetonitrile as precipitating solvent was used to extract ACT from rat plasma. ACT and an internal standard (mirabegron, IS) were separated on an Agilent poroshell EC C₁₈ column (50 × 3.0 mm, 2.7 µm) using methanol–10 mM ammonium acetate binary gradient mobile phase at a flow rate of 0.4 mL/min over 4 min run time. Detection was performed using target ions of [M + H]⁺ at m/z 451.2010 for ACT and m/z 397.1693 for IS in selective ion mode. The method was validated in the calibration range of 1.31–1000 ng/mL. All the validation parameters were well within the limits. The method demonstrated good performances in terms of intra‐ and inter‐day precision (3.27–12.60% CV) and accuracy (87.96–104.94%). Thus the present ultra‐high‐pressure liquid chromatograhy–high‐resolution mass spectrometry method for determination of ACT in rat plasma, is highly sensitive and rapid with a short run‐time of 4 min, can be suitable for high sample throughput and for large batches of biological samples in pharmacokinetic studies. This method can be extended to measure plasma concentrations of ACT in humans to understand drug metabolism, drug interaction and adverse effects. Copyright © 2015 John Wiley & Sons, Ltd.     

UPLC–MS/MS assay for simultaneous determination of four compounds in rat plasma: application to pharmacokinetic study after oral administration of Caulis Spatholobi extract

An ultra‐performance liquid chromatography tandem mass spectrometry method was developed for the simultaneous determination of protocatechuic acid, catechin, gallocatechin and formononetin in rat plasma, with genkwanin as the internal standard in this study. Plasma samples were prepared by liquid–liquid extraction with ethyl acetate. The four components were separated on an Agilent Zorbax Eclipse Plus C₁₈ column (2.1 × 50 mm, 1.8 μm) with the mobile phase consisting of water containing 0.05% formic acid and methanol (35:65, v/v), and detected by negative ion electrospray ionization in the selected reaction monitoring mode. The method was linear for all analytes over the investigated ranges, with all correlation coefficients >0.99. The validated lower limit of quantification was 0.5 ng/mL for protocatechuic acid, catechin, and gallocatechin and 0.8 ng/mL for formononetin. The intra‐ and inter‐day precisions (RSD, %) were <13.1%, and accuracy (RE, %) ranged from ?13.8 to 9.9%. The mean absolute extraction recoveries of the analytes and internal standard from rat plasma were all >80.7%. The validated method was successfully applied for the first time to investigate the pharmacokinetics of four chemical ingredients after oral administration of Caulis Spatholobi Extract in rats. Copyright © 2016 John Wiley & Sons, Ltd.     

Enhancing effect of borneol on pharmacokinetics of ginsenoside Rb1, ginsenoside Rg1, and notoginsenoside R1 in healthy volunteers after oral administration of compound Danshen dropping pills

Borneol (Bingpian), a monoterpenoid pharmaceutical ingredient, is commonly used as a main composition in traditional Chinese medicine preparations such as compound Danshen dropping pills (CDDP) and has also been approved by the U.S. Food and Drug Administration as a flavoring substance or adjuvant in food. Borneol plays a regulating and guiding role as a messenger drug in CDDP. However, the effect of borneol on the pharmacokinetics of the components of CDDP in human plasma is unclear. In this study, we investigate the effects of borneol on the pharmacokinetics of ginsenoside Rb₁ (Rb₁), ginsenoside Rg₁ (Rg₁), and notoginsenoside R₁ (NR₁) in CDDP. We used a double-cycle crossover-administration model in 12 healthy male volunteers, administered CDDP with borneol (drug T) and without borneol (drug R). The selective response monitoring mode was used for MS quantification in the positive mode. As a result, we found that borneol could significantly affect the pharmacokinetic parameters of notoginsenosides and increase the absorption and systemic exposure of Rb₁, Rg₁, and NR₁ in human plasma by ~1.85–3.71 times.     

超高效液相色谱-串联三重四极杆质谱分析法对大鼠血浆中三氯生的代谢和动力学研究

三氯生是一种被广泛应用在家庭卫生用品中的抗菌消毒剂。虽然其本身不具有很强的毒性,但其在生物体内的代谢变化是否对生物和人体有害我们还不得而知。因此,研究三氯生在动物体内的代谢与动力学情况是具有重要意义的。本文采用超高效液相色谱串联三级四极杆质谱法来测定口服给药(5 mg/kg)后大鼠血浆中的三氯生的含量及其代谢产物。相对于多反应监测(MRM)技术,尽管其有较好的最低检测限,但选择离子监测(SIR, 又称为SIM)有更好的方法验证参数。在本试验中,选择离子监测方法检测限为10.8 ng/mL,方法的回收率、准确度、精密度和重现性都较高。用该方法测定的三氯生在大鼠体内的消除半衰期为(48.5±10.5) h。同时,还鉴定出其三氯生血浆中有分别被羟基化加磺酸化、葡萄糖醛酸化以及磺酸化的4个代谢产物。     

In vivo microdialysis with ultra performance liquid chromatography–mass spectrometry for analysis of tetramethylpyrazine and its interaction with borneol in rat brain and blood

Tetramethylpyrazine (TMP) has been widely used in the treatment of ischemic cerebrovascular disease. However, the mechanism of TMP and how to increase its bioavailability need to be further explored. In our study, an in vivo microdialysis sampling technique coupled with ultra‐performance liquid chromatography–mass spectrometry method was developed to investigate the pharmacokinetic properties of TMP and its interaction with different doses of borneol (BO) in rats. Linearity of TMP in brain and blood dialysates exhibited good linear relationships over the concentration range of 0.991–555.14 ng/mL. The specificity, linearity, accuracy, precision, matrix effect and stability were within acceptable ranges. The results demonstrated that BO had a marked impact on the pharmacokinetic properties of TMP. After co‐administration, the areas under the concentration–time curve (AUC) of TMP in brain and blood were significantly increased. Meanwhile, the peak concentration of TMP in brain was also enhanced. The AUC_Brain/AUC_Blood of TMP, increased from 44% to 56 and 60.8% after co‐administration with BO (15 and 30 mg/kg). The pharmacodynamic results showed that TMP co‐administration with BO enhanced the cerebral blood flow during the period of ischemia and reduced the infarct volume. Overall, it might be an effective way to treat stroke to use TMP co‐administered with BO.     

Simultaneous determination of metacavir and its metabolites in rat plasma using high-performance liquid chromatography with tandem mass spectrometric detection (LC-MS/MS)

A sensitive and selective liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method for the simultaneous determination of metacavir and its two metabolites in rat plasma was developed and validated. Tinidazole was used as an internal standard and plasma samples were pretreated with one‐step liquid–liquid extraction. In addition, these analytes were separated using an isocratic mobile phase on a reverse‐phase C₁₈ column and analyzed by MS in the selected reaction monitoring mode. The monitored precursor to product‐ion transitions for metacavir, 2′,3′‐dideoxyguanosine, O‐methylguanine and the internal standard were m/z 266.0 → 166.0, m/z 252.0 → 152.0, m/z 166.0 → 149.0 and m/z 248.0 → 202.0, respectively. The standard curves were found to be linear in the range of 1–1000 ng/mL for metacavir, 5–5000 ng/mL for 2′,3′‐dideoxyguanosine and 1–1000 ng/mL for O‐methylguanine in rat plasma. The precision and accuracy for both within‐ and between‐batch determination of all analytes ranged from 2.83 to 9.19% and from 95.86 to 111.27%, respectively. No significant matrix effect was observed. This developed method was successfully applied to an in vivo pharmacokinetic study after a single intravenous dose of 20 mg/kg metacavir in rats. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantification and pharmacokinetic property of verubecestat an BACE1 inhibitor in rat plasma

In the present study, an ultra-performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS) approach was designed to measure the rat plasma levels of verubecestat with diazepam as the internal standard. Acetonitrile-based protein precipitation was applied for sample preparation, then the analyte verubecestat was subjected to gradient elution chromatography with a mobile phase composed of acetonitrile (A) and 0.1% formic acid in water (B). Verubecestat was monitored by m/z 410.1 → 124.0 transition for quantification by multiple reaction monitoring (MRM) in positive ion electrospray ionization (ESI) source. When the concentration of verubecestat ranged from 1 to 2500 ng/mL, the method exhibited good linearity. For verubecestat, the intra- and inter-day precision were determined with the values of 2.9–9.0% and 0.4–6.5%, respectively; and the accuracy ranged from −2.2% to 10.4%. Matrix effect, extraction recovery, and stability data were in line with the standard FDA guidelines for validating a bioanalytical method. The validity of the developed method was confirmed through the pharmacokinetic study.     

Micellar electrokinetic chromatographic determination of rosuvastatin in rabbit plasma and evaluation of its pharmacokinetics and interaction with niacin

A specific, accurate, precise and reproducible micellar electrokinetic chromatographic method was developed for in vitro and in vivo estimation of rosuvastatin, a synthetic and potent HMG‐CoA inhibitor, in rabbit plasma. Further, its pharmacokinetics in the presence of niacin, which could be co‐administered for monitoring of severe hypercholestremia, was investigated. The assay procedures involved simple liquid–liquid extraction of rosuvastatin and internal standard, atorvastatin, from a small plasma volume directly into acetonitrile. The organic layer was separated and evaporated under a gentle stream of nitrogen. The residue was reconstituted in the mobile phase and injected electrokinetically into electropherosis system. The background electrolyte consisted of borate buffer (25.0 mm , pH 9.5), 10.0% organic modifier (5.0% methanol + 5.0% acetonitrile) and 25.0 mm sodium dodecyl sulfate at 20.0 kV applied voltage and 215.0 nm detection wavelength for the effective separation of rosuvastatin, niacin and atorvastatin. Copyright © 2014 John Wiley & Sons, Ltd.     

Development and validation of a quantification method for oleanolic acid and hederagenin in rat plasma: application to the pharmacokinetic study

A rapid and sensitive liquid chromatography tandem mass spectrometry (LC–MS/MS) was developed and validated for simultaneous quantification of oleanolic acid and hederagenin in rat plasma. After the two analytes were extracted with liquid–liquid extraction, chromatographic separation was performed on a C₁₈ column with acetonitrile and water (85:15, v /v) as mobile phase at a flow rate of 0.4 mL/min. Calibration curves exhibited good linearity (r > 0.995) over the ranges of 0.41–82.0 ng/mL for oleanolic acid and 0.32–64.0 ng/mL for hederagenin, respectively. The lower limit of quantifications (LLOQs) in plasma were 0.41 ng/mL for oleanolic acid and 0.32 ng/mL for hederagenin. The established LLOQs were within the concentration needed for the assay in plasma, which met the requirements to evaluate their pharmacokinetics of oleanolic acid and hederagenin. This developed assay was successfully applied in the pharmacokinetic study of oleanolic acid and hederagenin in rats after oral administration of Rhizoma Clematidis extract.     

Determination and pharmacokinetics of periplocin in rat plasma by LC‐MS

A simple and sensitive LC‐MS method for the determination of periplocin in rat plasma was developed and validated. The chromatographic separation was carried out using a reverse‐phase Kromasil C₁₈ column(150 × 4.6 mm, i.d., 5 µm) with a mobile phase composed of methanol–water (76:24, v/v). The flow rate of mobile phase was 0.8 mL/min. The calibration curve was linear within the concentration range 1–1000 ng/mL. The intra‐ and inter‐day precisions across three validation days over the entire concentration range was lower than 9.2% in terms of relative standard deviation. Accuracy determined at three quality control concentrations ranged from ?2.0 to 6.0% in terms of relative error. The validated method was applied to the pharmacokinetic study of periplocin in rat plasma after intravenous and intramuscular administration. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of sparstolonin B by ultra‐high performance liquid chromatography coupled with triple quadrupole mass spectrometry: application to pharmacokinetic study of sparstolonin B in rat plasma

Sparstolonin B (SsnB), a spontaneous isocoumarin compound isolated from the tuber of Scirpus yagara Ohwi. (Cyperaceae), possesses potent anti‐inflammatory and antitumor activity. In the present study, a rapid and simple UHPLC/MS/MS method for determination of SsnB in rat plasma was developed and validated. Plasma samples were pretreated by liquid–liquid extraction with ethyl acetate containing rhein as an internal standard and separated on a C₁₈ column at 35 °C, with a gradient mobile phase consisting of acetonitrile and water containing 0.2% (v/v) formic acid within 2.1 min. MS/MS detection was accomplished in multiple reaction monitoring mode with negative electrospray ionization. The precursor–product ion transitions were m/z 266.9 [M–H]^? → m/z 211.0 for SsnB and m/z 283.2 [M–H]^? → m/z 239.0 for IS. The intra‐ and inter‐day precision (RSD) was <8.98% and the accuracy (RE) ranged from ?7.40 to 4.50%. The extraction recoveries ranged from 96.28 to 97.30%. The pharmacokinetic parameters were calculated using Win Nonlin53 software. The absolute bioavailability of SsnB was estimated to be 6.98%. The proposed method was successfully applied to a pharmacokinetic study of SsnB in rats after intravenous administration with a dose of 0.5 mg/kg and oral administration at a dose of 5 mg/kg. Copyright © 2015 John Wiley & Sons, Ltd.     

An accurate and reproducible method for simultaneous determination of four flavonoids in EtOAc extracts from Sophora flavescens Ait. in rat plasma based on UHPLC Q‐Exactive Mass spectrometry: Application to a pharmacokinetics study

In previous studies, it was revealed that ethyl acetate (EtOAc) extracts from Sophora flavescens Ait. improved glucose tolerance, reduced hyperglycemia, and restored insulin levels in diabetic patients. The aim of this study was to develop an accurate and sensitive UHPLC–MS method for simultaneous determination of flavonoids in EtOAc extracts of Kushen in rat plasma. Ethyl acetate–acetonitrile (2:1) was selected as the solvent to extract the four flavonoids from rat plasma. A BEH C₁₈ column (2.1 mm × 100 mm, 1.7 μm) with a C₁₈ guard cartridge was chosen as the separation plant using a gradient elution with acetonitrile (solvent A) and 0.1% formic acid (solvent B) in water. For all four analytes, the method showed good linearity (r² > 0.991) in 1–500 ng/mL. The inter‐ and intra‐day accuracy ranged from ?13.78 to 7.19%, and the precision (RSD) was <8.75%. Recoveries of all four flavonoids ranged from 85.9 to 101.3%. According to the results of multitarget pharmacokinetic studies, four active flavonoids in EtOAc extracts from Kushen have similar absorption kinetics but very different metabolic kinetics, and a double peak phenomenon was observed in the concentration–time curve of norkurarinone, which is different from the previous study. In conclusion, detection and multitarget pharmacokinetic studies successfully determined active flavonoids after oral administration of EtOAc extracts from Kushen by an efficient, sensitive and selective UHPLC–MS method, and the results may provide a foundation for future studies of Kushen.     

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.     

Simultaneous determination of seven ginsenosides in rat plasma by high‐performance liquid chromatography coupled to time‐of‐flight mass spectrometry: application to pharmacokinetics of Shenfu injection

A high‐performance liquid chromatography coupled to time‐of‐flight mass spectrometry (HPLC‐TOF MS) method was successfully developed and validated for the identification and determination of seven ginsenosides, R_e, R_f, R_b1, R_c, R_b2, R_o and R_d, in a Chinese herbal preparation, Shenfu injection, and rat plasma. Based on the method, the pharmacokinetic profiles of the seven ginsenosides were investigated following intravenous administration of single dose of Shenfu injection to six rats. The established method had high linearity, selectivity, sensitivity, accuracy and precision. The pharmacokinetic results showed that R_b1, R_c and R_b2 had similar pharmacokinetic profiles and relatively long half‐life values (19.29 ± 6.36, 29.54 ± 22.91 and 35.60 ± 30.66 h). The half‐lives of R_f and R_d were 4.21 ± 3.68 and 8.49 ± 5.20 h, respectively, indicating that they could be metabolized more rapidly than R_b1, R_c and R_b2. Copyright © 2014 John Wiley & Sons, Ltd.     

Simultaneous determination of three active components in rat plasma by UPLC–MS/MS: Application to pharmacokinetic study after oral administration of Herba Sarcandrae extract

A rapid, specific and sensitive ultra‐performance liquid chromatography tandem mass spectrometry (UPLC‐MS/MS) method was developed and validated for determination of isofraxidin, rosmarinic acid and kaempferol‐3‐O ‐glucuronide in rat plasma using warfarin as an internal standard (IS). Separation was conducted on a Thermo Hypersil GOLD C₁₈ column with linear gradient elution using methanol and water. Mass spectrometric detection was conducted using selected reaction monitoring (SRM) via an electrospray ionization (ESI) source. All analytes exhibited good linearity within their concentration ranges (r > 0.9990). The lower limits of quantitations of isofraxidin, rosmarinic acid, and kaempferol‐3‐O‐ glucuronide were 1.31, 0.67 and 0.92 ng/mL, respectively. Intra‐ and inter‐day precisions of these investigated components exhibited an RSD within 11.7%, and the accuracy ranged from −12.5 to 15.0% at all QC levels. The developed method was successfully applied to a pharmacokinetic study of isofraxidin, rosmarinic acid, and kaempferol‐3‐O‐ glucuronide in rats after oral administration of Herba Sarcandrae Extract.     

A simple LC‐MS method for determination of cyasterone in rat plasma: application to a pilot pharmacokinetic study

A simple, specific, and sensitive liquid chromatography–mass spectrometry (LC‐MS) method for determination of cyasterone in rat plasma was developed in our laboratory. Cucurbitacin B was used as an internal standard (IS). After protein precipitation with twofold volume of acetonitrile, the analyte and IS were separated on a Luna C₁₈ column (100 × 4.6 mm, i.d., 3.0 µm; Phenomenex) by isocratic elution with acetonitrile–water (80:20, v/v) as the mobile phase at a flow rate of 0.4 mL/min. An electrospray ionization source was applied and operated in the positive ion mode; selected ion monitoring scan mode was used for quantification, and the target ions m/z 543.3 for cyasterone and m/z 581.3 for IS were chosen. Good linearity was observed in the concentration range of 0.40–400 ng/mL for cyasterone in rat plasma. Intra‐day and inter‐day precision were both <7.4%. This method was proved to be suitable for pharmacokinetic studies after oral (5.0 mg/kg) or intravenous (0.5 mg/kg) administration of cyasterone in rats. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of rifampicin in rat plasma by modified large‐volume direct injection RAM‐HPLC and its application to a pharmcokinetic study

A direct large volume injection high‐performance liquid chromatography (HPLC) method with homemade restricted‐access media (RAM) pre‐column and combined with a column‐switching valve was established and developed for determination rifampicin (RIP) in rat plasma. The rat plasma samples (100 μL) were injected directly onto pre‐column, where RIP was retained and pre‐concentrated, while proteins were washed to waste using a methanol–water (5:95) as the mobile phase at a flow rate of 1 mL/min. Then, by rotation of the switching valve at 5 min, the RIP were eluted from the pre‐column and transferred to an Luna C₁₈ analytical column by the chromatographic mobile phase consisting of methanol–acetonitrile–10 mm ammonium format (60:5:35) at a flow rate of 1 mL/min. The total analytical run time was 15 min with UV detection wavelength at 254 nm. Carbamazepine was used as the internal standard. Excellent linear correlation (r = 0.9993) was obtained in the range of 0.25–8 µg/mL for rat plasma. The intra‐day and inter‐day precisions of RIP were all <5.0%. The recoveries were in the range of from 99.98–113.66% for plasma. This on‐line RAM‐HPLC method was successfully applied to the pharmacokinetic study of RIP in rat plasma. Copyright © 2014 John Wiley & Sons, Ltd.