Quantitation of bivalirudin,a novel anticoagulant peptide,in human plasma by LC-MS/MS:Method development,validation and application to pharmacokinetics

A rapid and sensitive method based on liquid chromatographtandem mass spectrometry （LC-MS/MS） for the determination of a novel anticoagulant peptide bivalirudin in human plasma has been developed and validated. Plasma samples were precipitated protein with acetonitrile and reextracted with dichloromethane, after which the analyte and triptorelin as an internal standard （IS） were separated on a 300SB-Cl8 column （150 mm x 4.6 mm i.d., 5 gm particle size） using 0.1% formic acid：methanol （45：55, v/v） as mobile phase. The triple-quadrupole mass spectrometer, equipped with electrospray ionization （ESI） interface, was operated in the positive ion mode, and the multiplereaction monitoring （MRM） transitions of bivalirudin and IS were at m/z 1091.0-650.4 and m/z656.5 - 249.3, respectively. The lower limit of quantification （LLOQ） was 1 ng/mL for 100 ng/mL plasma sample and the assay was linear over the concentration range 1 1000 ng/mL. The accuracy was within a range from -0.4% to 0.5% in terms of relative error （RE） and the intra- and inter-day precisions in terms of relative standard deviation （RSD） were 〈2.92 and 〈 3.36, respectively. The method was successfully applied to a pharmacokinetic study involving intravenous administration of bivalirudin （0.5 mg/kg） to Chinese volunteers.

Helicobacter pylori serology in a birth cohort of New Zealanders from age 11 to 26

AIM: To determine seroprevalence of Helicobacter pylori (Hpylori) in the Dunedin Multidisciplinary Health and Development Study (DMHDS) at age 26 in order to investigate seroconversion and seroreversion from age 11 to 26 and the association of seropositivity with risk factors for Hpylori infection.METHODS: Participants in the DMHDS at age 26 and retrospectively at age 21 were tested for H pylori antibodies using two commercially available ELISA kits. Gender, socioeconomic status (SES), smoking, educational attainment and employment at age 26 were tested for association with H pylori seropositivity.RESULTS: At ages 21 and 26, seroprevalence of Hpylori using one or other kit was 4.2% (n = 795) and 6.3% (n = 871) respectively. Seroreversion rate was lower than seroconversion rate (0.11% vs0.53% per person-year) in contrast to the period from age 11 to 21 when seroreversion rate exceeded seroconversion rate (0.35% vs 0.11% perperson-year). Serology in those tested at ages 11, 21,and 26 remained unchanged in 93.6% of the sample.Seroprevalence at age 26 was lower among those with a secondary school qualification (P = 0.042) but was not associated with gender, SES, smoking or employment status.CONCLUSION: Hpylodseroprevalence in a New Zealand birth cohort remains low between ages 11 and 26. H pylori infection remains stable from childhood to adulthood although seroreversion seems to be more common in the adolescent years than in young adults.

Determination of repaglinide in human plasma by high-performance liquid chromatography–tandem mass spectrometry

A rapid and sensitive method based on high-performance liquid chromatography–tandem mass spectrometry(LC–MS/MS)has been developed for the determination of repaglinide in human plasma.The analyte and internal standard(I.S.),diazepam,were extracted from plasma(25 mL)by liquid–liquid extraction with diethyl ether–dichloromethane(60:40,v/v)and separated on a XDB-C_(18) column using acetonitrile–ammonium acetate buffer(pH 6.8,0.01 mol/L)as mobile phase.The retention times of repaglinide and I.S.were 1.95 and 2.35 min,respectively.Detection was carried out using API 4000 mass spectrometer with an ESI interface operating in the multiple reaction monitoring(MRM)mode.The assay was linear over the concentration range 0.050–50 ng/mL with a limit of detection(LOD)of 0.010 ng/mL.Intra-and inter-day precisions(as relative standard deviation,R.S.D.)were ≤5.07%and ≤11.2%,respectively,and accuracy(as relative error,R.E.)was from-0.593%to -1.26%.The assay was successfully applied to a pharmacokinetic study involving a single oral administration of a tablet containing 2 mg repaglinide to each of 10 healthy volunteers.

Separation and simultaneous quantitation of PGF2α and its epimer 8-iso-PGF2α using modifier-assisted differential mobility spectrometry tandem mass spectrometry

Because many therapeutic agents are contaminated by epimeric impurities or form epimers as a result of metabolism, analytical tools capable of determining epimers are increasingly in demand. This article is a proof-of-principle report of a novel DMS–MS/MS method to separate and simultaneously quantify epimers, taking PGF2α and its 8-epimer, 8-iso-PGF2α, as an example. Good accuracy and precision were achieved in the range of 10–500 ng/m L with a run time of only 1.5 min. Isopropanol as organic modifier facilitated a good combination of sensitivity and separation. The method is the first example of the quantitation of epimers without chromatographic separation.

Biological fate and interaction with cytochromes P450 of the nanocarrier material,D-α-tocopheryl polyethylene glycol 1000 succinate

D-a-Tocopheryl polyethylene glycol 1000 succinate(TPGS,also known as vitamin E-TPGS)is a biodegradable amphiphilic polymer prepared by esterification of vitamin E with polyethylene glycol(PEG)1000.It is approved by the US Food and Drug Administration(FDA)and has found wide application in nanocarrier drug delivery systems(NDDS).Fully characterizing the in vivo fate and pharmacokinetic behavior of TPGS is important to promote the further development of TPGS-based NDDS.However,to date,a bioassay for the simultaneous quantitation of TPGS and its metabolite,PEG1000,has not been reported.In the present study,we developed such an innovative bioassay and used it to investigate the pharmacokinetics,tissue distribution and excretion of TPGS and PEG1000 in rat after oral and intravenous dosing.In addition,we evaluated the interaction of TPGS with cytochromes P450(CYP450s)in human liver microsomes.The results show that TPGS is poorly absorbed after oral administration with very low bioavailability and that,after intravenous administration,TPGS and PEG1000 are mainly distributed to the spleen,liver,lung and kidney before both being slowly eliminated in urine and feces as PEG1000.In vitro studies show the inhibition of human CYP450 enzymes by TPGS is limited to a weak inhibition of CYP3A4.Overall,our results provide a clear picture of the in vivo fate of TPGS which will be useful in evaluating the safety of TPGS-based NDDS in clinical use and in promoting their further development.