Enantiomeric determination of tramadol and O-desmethyltramadol in human plasma by fast liquid chromatographic technique coupled with mass spectrometric detection

A rapid and sensitive method using liquid chromatography–tandem mass spectrometry (LC–MS/MS) for enantiomeric determination of tramadol and its primary phase metabolite O-desmethyltramadol in human plasma has been developed. Tramadol hydrochloride – ¹³C, d_3, was used as an isotopic labeled internal standard for quantification. The method involves a simple solid phase extraction. The analytes and internal standard were separated on Lux Cellulose-2 packed with cellulose tris(3-chloro-4-methylphenylcarbamate) using isocratic elution with hexane/isopropanol/diethylamine (90:10:0.1, v/v/v) at a flow rate of 1.3 mL/min. The APCI positive ionization mass spectrometry was used with multiple reaction monitoring of the transitions at m/z 264.2 → 58.2 for tramadol, m/z 250.1 → 58.2 for O-desmethyltramadol and m/z 268.2 → 58.2 for internal standard. Linearity was achieved between 1–800 ng/mL and 1–400 ng/mL (R² ≥ 0.999) for each enantiomer of tramadol and O-desmethyltramadol, respectively. Intra-day accuracies ranged among 98.2–102.8%, 97.1–109.1% and 97.4–102.9% at the lower, intermediate, and high concentration for all analytes, respectively. Inter-day accuracies ranged among 95.5–104.1%, 99.2–104.7%, and 94.2–105.6% at the lower, intermediate, and high concentration for all analytes, respectively. This assay was successfully used to determine the concentration of enantiomers of tramadol and O-desmethyltramadol in a pharmacogenetic study.     

Spatial factors contribute to benthic diatom structure in streams across spatial scales: Considerations for biomonitoring

Diatoms are widely used in the biological monitoring of streams because they are strong responders to environmental change, but dispersal and spatial factors can play important and potentially confounding roles in the presence, absence, and abundance of species along with characterizing species–environment relationships. To examine how spatial factors affect diatom community structure and biomonitoring, multiple scales were sampled including the Western Allegheny Plateau (n = 58), Leading Creek watershed (n = 18), and the adjacent Shade River watershed (n = 21) in southeast Ohio. Partitioning of spatial, environmental, and spatially-structured environmental variation was conducted on diatom assemblages and on diatom metrics used in biomonitoring. At the regional scale, diatom assemblages and metrics had strong relationships with agricultural (e.g., significant correlations with nutrients, conductivity, and pasture/row crops in the watershed) and alkalinity gradients. Diatom assemblages and metrics in both watersheds were strongly associated with acid mine drainage (AMD) impacts, and when spatial factors were set as covariables in CCAs, relationships with AMD gradients became even stronger, indicating the need to consider how spatial factors could reduce the strength of diatom-environment relationships. Metrics calculated at all scales had very little variation explained exclusively by spatial factors, likely because multiple species are combined into a simplified metric that reduces the effects of species dispersal. Local environmental variables accounted for 57, 42, and 42% of the total variation explained (TVE), and spatial variables accounted for 28, 31, and 37% of the TVE in the regional, Leading Creek, and Shade River datasets, respectively. The amounts of variation in diatom assemblages explained solely by spatial factors at these scales were substantial and similar to what has been reported at continental, national, and large regional (Level I Omernik ecoregions) scales (approximately 1/3 of TVE). Although amounts of variation explained are similar across scales, processes underlying the spatial structure likely differ. In addition to describing ecological patterns, recognizing the potential influence of spatial factors could improve the identification and management of environmental problems at a range of scales, as well as aid in the development of new research questions and hypotheses aimed at exploring factors that could explain portions of the spatially explicit variation.     

Simple and selective method for the determination of various tyrosine kinase inhibitors used in the clinical setting by liquid chromatography tandem mass spectrometry

A fast, sensitive, universal and accurate method for the determination of four different tyrosine kinase inhibitors from biological material was developed using LC–MS/MS techniques. Utilizing a simple protein precipitation with acetonitrile a 20 μl sample volume of biological matrixes can be extracted at 4 °C with minimal effort. After centrifugation the sample extract is introduced directly onto the LC–MS/MS system without further clean-up and assayed across a linear range of 1–4000 ng/ml. Chromatography was performed using a Dionex Ultimate 3000 with a Phenomenex prodigy ODS3 (2.0 mm × 100 mm, 3 μm) column and eluted at 200 μl/min with a tertiary mobile phase consisting of 20 mM ammonium acetate:acetonitrile:methanol (2.5:6.7:8.3%). Injection volume varied from 0.1 μl to 1 μl depending on the concentration of the drug observed. Samples were observed to be stable for a maximum of 48 h after extraction when kept at 4 °C. Detection was performed using a turbo-spray ionization source and mass spectrometric positive multi-reaction-monitoring-mode (+MRM) for Gefitinib (447.1 m/z; 127.9 m/z), Erlotinib (393.9 m/z; 278.2 m/z), Sunitinib (399.1 m/z; 283.1 m/z) and Sorafenib (465.0 m/z; 251.9 m/z) at an ion voltage of +3500 V. The accuracy, precision and limit-of-quantification (LOQ) from cell culture medium were as follows: Gefitinib: 100.2 ± 3.8%, 11.2 nM; Erlotinib: 101.6 ± 3.7%, 12.7 nM; Sunitinib: 100.8 ± 4.3%, 12.6 nM; Sorafenib: 93.9 ± 3.0%, 10.8 nM, respectively. This was reproducible for plasma, whole blood, and serum. The method was observed to be linear between the LOQ and 4000 ng/ml for each analyte. Effectiveness of the method is illustrated with the analysis of samples from a cellular accumulation investigation and from determination of steady state concentrations in clinically treated patients.     

Simultaneous determination of tolbutamide,omeprazole, midazolam and dextromethorphan in human plasma by LC–MS/MS—A high throughput approach to evaluate drug–drug interactions

Drug–drug interactions involving cytochrome P450 (CYP450s) are an important factor for evaluation of a new chemical entity (NCE) in drug development. To evaluate the potential inhibitory effects of a NCE on the pharmacokinetics of a cocktail of representative probes of CYP enzymes (midazolam for CYP3A4, tolbutamide for CYP2C9, omeprazole for CYP2C19 and dextromethorphan for CYP2D6) and the safety and tolerability of the NCE in the presence of probe substrates, a high throughput liquid chromatography/tandem mass spectrometry (LC–MS/MS) method was developed and validated for the simultaneous determination of tolbutamide, omeprazole, midazolam and dextromethorphan in human plasma using tolbutamide-d₉, midazolam-d₄, (±)-omeprazole-d₃, and dextromethorphan-d₃ as the internal standards (ISs). Human plasma samples of 50 μL were extracted by a simple protein-precipitation procedure and analyzed using a high performance liquid chromatography electrospray tandem mass spectrometer system. Reversed-phase HPLC separation was achieved with a Hypersil GOLD AQ column (50 mm × 4.6 mm, 5 μm). MS/MS detection was set at mass transitions of 271 → 172 m/z for tolbutamide, 346 → 198 m/z for omeprazole, 326 → 291 m/z for midazolam, 272 → 171 m/z for dextromethorphan, 280 → 172 m/z for tolbutamide-d₉ (IS), 349 → 198 m/z for (±)-omeprazole-d₃ (IS), 330 → 295 m/z for midazolam-d₄ (IS), and 275 → 171 m/z for dextromethorphan-d₃ (IS) in positive mode. The high throughput LC–MS/MS method was validated for accuracy, precision, sensitivity, stability, recovery, matrix effects, and calibration range. Acceptable intra-run and inter-run assay precision (<10%) and accuracy (<10%) were achieved over a linear range of 50–50,000 ng/mL for tolbutamide, 1–1000 ng/mL for omeprazole, 0.1–100 ng/mL for midazolam and 0.05–50 ng/mL for dextromethorphan in human plasma. Method robustness was demonstrated by the 100% pass rate of 24 incurred sample analysis runs and all of the 50 clinical study samples used for incurred sample reproducibility (ISR) test having met the acceptance criterion (%Diff within 20%). The overall ISR results for all compounds showed that over 95% of the samples had a %Diff of less than 10%. The method is simple, rapid and rugged, and has been applied successfully to sample analysis in support of a drug–drug interaction study.     

Determination of picamilon concentration in human plasma by liquid chromatography–tandem mass spectrometry

A rapid liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated for the determination of picamilon concentration in human plasma. Picamilon was extracted from human plasma by protein precipitation. High performance liquid chromatography separation was performed on a Venusil ASB C₁₈ column with a mobile phase consisting of methanol ?10 mM ammonium acetate–formic acid (55:45:01, v/v/v) at a flow rate of 0.65 ml/min. Acquisition of mass spectrometric data was performed in selected reaction monitoring mode, using the transitions of m/z 209.0 → m/z (78.0 + 106.0) for picamilon and m/z 152.0 → m/z (93.0 + 110.0) for paracetamol (internal standard). The method was linear in the concentration range of 1.00–5000 ng/ml for the analyte. The lower limit of quantification was 1.00 ng/ml. The intra- and inter-assay precision were below 13.5%, and the accuracy was between 99.6% and 101.6%. The method was successfully applied to characterize the pharmacokinetic profiles of picamilon in healthy volunteers. This validated LC–MS/MS method was selective and rapid, and is suitable for the pharmacokinetic study of picamilon in humans.     

Simultaneous determination of triprolidine and pseudoephedrine in human plasma by liquid chromatography–ion trap mass spectrometry

A highly efficient, selective and specific method for simultaneous quantitation of triprolidine and pseudoephedrine in human plasma by liquid chromatography–ion trap-tandem mass spectrometry coupled with electro spray ionization (LC–ESI-ion trap-tandem MS) has been validated and successfully applied to a clinical pharmacokinetic study. Both targeted compounds together with the internal standard (gabapentin) were extracted from the plasma by direct protein precipitation. Chromatographic separation was achieved on a C₁₈ ACE^® column (50.0 mm × 2.1 mm, 5 μm, Advance Chromatography Technologies, Aberdeen, UK), using an isocratic mobile phase, consisting of water, methanol and formic acid (55:45:0.5, v/v/v), at a flow-rate of 0.3 mL/min. The transition monitored (positive mode) was m/z 279.1 → m/z 208.1 for triprolidine, m/z 165.9 → m/z 148.0 for pseudoephedrine and m/z 172.0 → m/z 154.0 for gabapentin (IS). This method had a chromatographic run time of 5.0 min and a linear calibration curves ranged from 0.2 to 20.0 ng/mL for triprolidine and 5.0–500.0 ng/mL for pseudoephedrine. The within- and between-batch accuracy and precision (expressed as coefficient of variation, %C.V.) evaluated at four quality control levels were within 94.3–106.3% and 1.0–9.6% respectively. The mean recoveries of triprolidine, pseudoephedrine and gabapentin were 93.6, 76.3 and 82.0% respectively. Stability of triprolidine and pseudoephedrine was assessed under different storage conditions. The validated method was successfully employed for the bioequivalence study of triprolidine and pseudoephedrine formulation in twenty six volunteers under fasting conditions.     

Quantification of isradipine in human plasma using LC–MS/MS for pharmacokinetic and bioequivalence study

A highly sensitive and rapid method for the analysis of isradipine in human plasma using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) was developed. The procedure involves a simple liquid–liquid extraction of isradipine and amlodipine (IS, internal standard) with methyl-t-butyl ether after alkaline treatment and separation by RP-HPLC. Detection was performed by positive ion electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode, monitoring the transitions m/z 372.1 → m/z 312.2 and m/z 408.8 → m/z 237.9, for quantification of isradipine and IS, respectively. The standard calibration curves showed good linearity within the range of 10 to 5000 pg/mL (r² ≥ 0.9998). The lower limit of quantitation (LLOQ) was 10 pg/mL. The retention times of isradipine (0.81 min) and IS (0.65 min) suggested the potential for high throughput of the proposed method. In addition, no significant metabolic compounds were found to interfere with the analysis. This method offered good precision and accuracy and was successfully applied for the pharmacokinetic and bioequivalence studies of 5 mg of sustained-release isradipine in 24 healthy Korean volunteers.     

Epiphytic lichen indication of nitrogen deposition and climate in the northern rocky mountains,USA

Lichen bioindication can provide economical and spatially extensive monitoring of climate and pollution impacts on ecological communities. We used non-metric multidimensional scaling of lichen community composition and generalized additive models to analyze regional climate and pollution gradients in the northern Rocky Mountains, U.S. Temperature extremes, relative humidity, and N-deposition were strongly related to lichen community composition. Eutrophic species (genera Physcia, Xanthomendoza, and Xanthoria) were associated with high N deposition, low precipitation, and temperature extremes. Estimated N deposition in our study ranged from <0.5 to 4.26 kg N ha⁻¹ year⁻¹ with degradation to lichen communities observed at 4.0 kg N ha⁻¹ year⁻¹, the indicated critical load. The resulting model can track changes in climate and N pollution related to lichen communities over time, identify probable sensitive or impacted habitats, and provide key information for natural resource management and conservation. The approach is broadly applicable to temperate ecosystems worldwide.     

Direct relationship between osmotic and ionic conforming behavior and tissue water regulatory capacity in echinoids

Echinoderms are considered marine osmoconforming invertebrates. However, many are intertidal or live next to estuaries, tolerating salinity changes and showing extracellular gradients to dilute seawater. Three species of echinoids – Lytechinus variegatus, which can occur next to estuarine areas, the rocky intertidal Echinometra lucunter, and the mostly subtidal Arbacia lixula – were submitted to a protocol of stepwise (rate of 2–3 psu/h) dilution, down to 15 psu, or concentration, up to 45 psu, of control seawater (35 psu). Coelomic fluid samples were obtained every hour. The seawater dilution experiment lasted 8 h, while the seawater concentration experiment lasted 6 h. Significant gradients (40–90% above value in 15 psu seawater) for osmolality, sodium, magnesium, and potassium were shown by L. variegatus and E. lucunter. A. lixula showed the smallest gradients, displaying the strongest conforming behavior. The esophagus of the three species was challenged in vitro with 20 and 50% osmotic shocks (hypo- and hyperosmotic). A. lixula, the most “conforming” species, showed the highest capacity to avoid swelling of its tissues upon the ? 50% hyposmotic shock, and was also the species less affected by salinity changes concerning the observation of spines and ambulacral feet movement in the whole-animal experiments. Thus, the most conforming species (A. lixula) displayed the highest capacity to regulate tissue water/volume, and was also the most euryhaline among the three studied species. In addition, tissues from all three species swelled much more than they shrank under osmotic shocks of same magnitude. This distinct trend to gain water, despite the capacity to hold some gradients upon seawater dilution, helps to explain why echinoderms cannot be fully estuarine, or ever enter fresh water.     

Simultaneous quantification of rosiglitazone and its two major metabolites,N-desmethyl and p-hydroxy rosiglitazone in human plasma by liquid chromatography/tandem mass spectrometry: Application to a pharmacokinetic study

We present a simple, rapid, and sensitive liquid chromatography (LC)–tandem mass spectrometry (MS/MS) method for the simultaneous quantification of rosiglitazone and its two major metabolites via CYP2C8/9, N-desmethyl and p-hydroxy rosiglitazone, in human plasma. The procedure was developed and validated using rosiglitazone-d₃ as the internal standard. Plasma samples (0.1 ml) were prepared using a simple deproteinization procedure with 0.2 ml of acetonitrile containing 40 ng/ml of rosiglitazone-d₃. Chromatographic separation was carried out on a Luna C₁₈ column (100 mm × 2.0 mm, 3-μm particle size) using an isocratic mobile phase consisting of a 60:40 (v/v) mixture of acetonitrile and 0.1% formic acid_(aq). Each sample was run at 0.2 ml/min for a total run time of 2.5 min per sample. Detection and quantification were performed using a mass spectrometer in selected reaction-monitoring mode with positive electrospray ionization at m/z 358.1 → 135.1 for rosiglitazone, m/z 344.2 → 121.1 for N-desmethyl rosiglitazone, m/z 374.1 → 151.1 for p-hydroxy rosiglitazone, and m/z 361.1 → 138.1 for rosiglitazone-d₃. The linear ranges of concentration for rosiglitazone, N-desmethyl rosiglitazone, and p-hydroxy rosiglitazone were 1–500, 1–150, and 1–25 ng/ml, respectively, with a lower limit of quantification of 1 ng/ml for all analytes. The coefficient of variation for assay precision was less than 14.4%, and the accuracy was 93.3–112.3%. No relevant cross-talk and matrix effect were observed. This method was successfully applied to a pharmacokinetic study after oral administration of a 4-mg rosiglitazone tablet to healthy male Korean volunteers.     

Quantitative analysis of RU38486 (mifepristone) by HPLC triple quadrupole mass spectrometry

A sensitive liquid chromatography–mass spectrometric method was validated for the quantification of RU38486 (mifepristone) in human and murine plasma. The analyte and internal standard (alfaxolone) were extracted by liquid–liquid extraction with diethyl ether, resolved on a C18 column using gradient elution with methanol and ammonium acetate and detected after positive electrospray ionization (m/z 430 → 372; m/z 333 → 297, respectively). Quantification was linear over the range 0.5–500 ng (r² > 0.997), precise and accurate (intra-assay RSD ≤ 7.2%, RME ≤ 8.2%; inter-assay RSD ≤ 15.7% RME ≤ 10.2%). The limit of quantification (LOQ) was 50 pg injected on column, permitting reproducible analysis of RU38486 in small volumes of plasma.     

Determination of metoclopramide in human plasma by LC–ESI-MS and its application to bioequivalance studies

An LC–MS method for the determination of metoclopramide in human plasma was developed and validated. Sample preparation involved extraction with ethyl acetate. Chromatographic separation was performed on a Thermo Hypersil-Hypurity C₁₈ (150 mm × 2.1 mm, 5 μm) with the mobile phase consisting of 40 mM ammonium acetate–methanol–acetonitrile. A single-quadrupole mass spectrometer with an electrospray interface was operated in the selected-ion monitoring mode to detect the [M+H]⁺ ions at m/z 300 for metoclopramide and at m/z 384 for the internal standard (prazosin). The method was validated over 0.78–50.00 ng mL^?1 for metoclopramide. The recovery was 67.8–83.1%, and the limit of quantitation (LOQ) detection was 0.78 ng mL^?1 for metoclopramide. The intra- and inter-day precision of the method at three concentrations was 5.0–13.6% with accuracy of 99.2–104.0%. Stability of compounds was established in a battery of stability studies. The method was successfully applied to bioequivalence studies of metoclopramide hydrochloride tablets to obtain the pharmacokinetic parameters.     

Liquid chromatography/tandem mass spectrometry method for the simultaneous determination of vardenafil and its major metabolite,N-desethylvardenafil,in human plasma: Application to a pharmacokinetic study

A rapid and sensitive LC–MS/MS method for the determination of vardenafil and its major metabolite, N-desethylvardenafil, in human plasma using sildenafil as an internal standard was developed and validated. The analytes were extracted from 0.25-mL aliquots of human plasma by liquid–liquid extraction, using 1 mL of ethyl acetate. Chromatographic separation was carried on a Luna C₁₈ column (50 mm × 2.0 mm, 3 μm) at 40 °C, with an isocratic mobile phase consisting of 10 mM ammonium acetate (pH 5.0) and acetonitrile (10:90, v/v), a flow rate of 0.2 mL/min, and a total run time of 2 min. Detection and quantification were performed using a mass spectrometer in the selected reaction-monitoring mode with positive electrospray ionization at m/z 489.1 → 151.2 for vardenafil, m/z 460.9 → 151.2 for N-desethylvardenafil, and m/z 475.3 → 100.1 for the internal standard (IS), respectively. This assay was linear over a concentration range of 0.5–200 ng/mL with a lower limit of quantification of 0.5 ng/mL for both vardenafil and N-desethylvardenafil. The coefficient of variation for the assay precision was <13.6%, and the accuracy was >93.1%. This method was successfully applied to a pharmacokinetic study after oral administration of vardenafil 20 mg tablet in Korean healthy male volunteers.     

Performance of tiloronoxim and tilorone determination in human blood by HPLC–MS/MS: Method validation,uncertainty assessment and its application to a pharmacokinetic study

A highly sensitive and selective HPLC–MS/MS method is presented for the quantitative determination of tiloronoxim and its metabolite tilorone in human blood. An aliquot of 200 μl human blood was extracted with a mixture of chloroform/ethyl ether (1/2, v/v), using metoprolol as the internal standard (the IS). Separation was achieved on an Xterra MS C18 column (50 mm × 2.1 mm, 5 μm) with a gradient mobile phase of methanol/water containing 15 mM ammonium bicarbonate (pH 10.5). Detection was performed using positive MRM mode on a TurboIonSpray source. The mass transitions monitored were m/z 426.3 → 100.0, m/z 411.3 → 100.0 and m/z 268.3 → 116.1 for tiloronoxim, tilorone and the IS, respectively. The method was fully validated using total error theory, which is based on β-expectation tolerance intervals and include trueness and intermediate precision. The method was found to be accurate over a concentration range of 1–100 ng/ml for both compounds. The measurement uncertainty based on β-expectation tolerance intervals was assessed at each concentration level of the validation standards. This method was successively applied to a pharmacokinetic study of tiloronoxim in healthy volunteers.     

Prediction of all-cause mortality with copeptin in cardio-cerebrovascular patients: A meta-analysis of prospective studies

BackgroundMeasurement of the biomarker copeptin may help identify disease severity and risk of mortality for a various diseases. This study sought to determine the relationship between copeptin and all-cause mortality of patients with cardio-cerebrovascular disease.MethodsDatabase of Medline and Web of Science were searched for studies with data involving the baseline copeptin levels and subsequent all-cause mortality outcomes. The pooled HRs of all-cause mortality were calculated and presented with 95%CIs. Subgroup analysis and sensitivity analysis were conducted to explore the possible sources of heterogeneity.ResultsData from 14,395 participants were derived from 28 prospective studies. Higher copeptin significantly increased the risk of all-cause mortality (per unit copeptin: HR = 1.020, 95%CI = 1.004–1.036; log unit copeptin: HR = 2.884, 95%CI = 1.844–4.512; categorical copeptin: HR = 3.371, 95%CI = 2.077–5.472). Subgroup analysis indicated that the risk of all-cause death was higher in cerebrovascular patients (per unit copeptin: HR = 2.537, 95%CI = 0.956–6.731; log unit copeptin: HR = 3.419, 95%CI = 2.391–4.888) than cardiovascular patients (per unit copeptin: HR = 1.011, 95%CI = 1.002–1.020; log unit copeptin: HR = 2.009, 95%CI = 1.119–3.608).ConclusionCopeptin is associated with all-cause mortality of patients with cardiovascular and cerebrovascular disease. Our study suggests that copeptin seems to be a promising novel biomarker for prediction of mortality in cardio-cerebrovascular patients, especially for cerebrovascular patients.     

Simultaneous determination of bisoprolol and hydrochlorothiazide in human plasma by HPLC coupled with tandem mass spectrometry

A sensitive, specific and selective method has been developed for the simultaneous determination of bisoprolol and hydrochlorothiazide in human plasma. The method employed a state of the art LC–MS/MS operated in the positive and negative ionization switching modes. A simple sample preparation step involving protein precipitation with acetonitrile has been optimized; the analytes and the internal standard moxifloxacin were separated on a Purosphere^® STAR C₈ column (125 mm × 4 mm, 5 μm). The mobile phase was an ammonium acetate solution (1 mM) with formic acid (0.2%): methanol and acetonitrile (65:17.5:17.5, v/v/v (%)), the flow rate was set at 0.65 mL/min. Bisoprolol and hydrochlorothiazide were ionized using ESI source prior to detection by Multiple Reaction Monitoring (MRM) mode while monitoring at the following transitions: positive m/z 326 → 116 for bisoprolol, negative m/z 296 → 269 and m/z 296 → 205 for hydrochlorothiazide. Linearity was demonstrated over the concentration range 0.10–30.0 (ng/mL) for bisoprolol and 1.00–80.00 ng/mL for hydrochlorothiazide. The limits of detection were 0.100 (ng/mL) for bisoprolol and 1.00 (ng/mL) for hydrochlorothiazide. The validated method was successfully applied to a pharmacokinetic study of 5 mg bisoprolol fumarate with 12.5 mg hydrochlorothiazide tablet in healthy volunteers.     

Simultaneous determination of puerarin,daidzein, baicalin,wogonoside and liquiritin of GegenQinlian decoction in rat plasma by ultra-performance liquid chromatography–mass spectrometry

A specific ultra-performance liquid chromatography–mass spectrometry (UPLC–MS) method was developed for the simultaneous determination of puerarin, daidzein, baicalin, wogonoside and liquiritin in rat plasma. Chromatographic separation was performed on a C₁₈ column packed with 1.7 μm particles by a linear gradient elution. The analytes and carbamazepine (internal standard, I.S.) were monitored in a selected-ion reaction (SIR) mode with a positive electrospray ionization (ESI) interface by the following ions: m/z 417.2 for puerarin, m/z 255.2 for daidzein, m/z 271.0 for baicalin, m/z 461.0 for wogonoside, m/z 441.0 for liquiritin and m/z 237.2 for carbamazepine (I.S.), respectively. The calibration curves of these analytes were linear over the concentration ranges from 0.00254–1.02 μg mL^?1 to 0.0102–10.2 μg mL^?1. Within-batch and between-batch precisions (RSD%) were all within 15% and accuracy (RE%) ranged from ?10% to 10%. The extraction recoveries were on average 79.8% for puerarin, 90.8% for daidzein, 74.4% for baicalin, 70.2% for wogonoside and 84.7% for liquiritin. The validated method was successfully applied to investigate the pharmacokinetics of five bioactive compounds of GegenQinlian decoction (GQD) in rats.     

Urban–rural disparities of child health and nutritional status in China from 1989 to 2006

This paper analyzes urban–rural disparities of China's child health and nutritional status using the China Health and Nutrition Survey data from 1989 to 2006. We investigate degrees of health and nutritional disparities between urban and rural children in China as well as how such disparities have changed during the period 1989–2006. The results show that on average urban children have 0.29 higher height-for-age z-scores and 0.19 greater weight-for-age z-scores than rural children. Urban children are approximately 40% less likely to be stunted (OR = 0.62; p < 0.01) or underweight (OR = 0.62; p < 0.05) during the period 1989–2006. We also find that the urban–rural health and nutritional disparities have been declining significantly from 1989 to 2006. Both urban and rural children have increased consumption of high protein and fat foods from 1989 to 2006, but the urban–rural difference decreased over time. Moreover, the urban–rural gap in child preventive health care access was also reduced during this period.     

Stability evaluation and sensitive determination of antiviral drug,valacyclovir and its metabolite acyclovir in human plasma by a rapid liquid chromatography–tandem mass spectrometry method

A simple, sensitive and high throughput liquid chromatography/positive-ion electrospray ionization mass spectrometry (LC–ESI-MS/MS) method has been developed for the simultaneous determination of valacyclovir and acyclovir in human plasma using fluconazole as internal standard (IS). The method involved solid phase extraction of the analytes and IS from 0.5 mL human plasma with no reconstitution and drying steps (direct injection of eluate). The chromatographic separation was achieved on a Gemini C18 analytical column using isocratic mobile phase, consisting of 0.1% formic acid and methanol (30:70 v/v), at a flow-rate of 0.8 mL/min. The precursor → product ion transition for valacyclovir (m/z 325.2 → 152.2), acyclovir (m/z 226.2 → 152.2) and IS (m/z 307.1 → 220.3) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) mode. The method was validated over the concentration range 5.0–1075 ng/mL and 47.6–10225 ng/mL for valacyclovir and acyclovir respectively. The mean recovery of valacyclovir (92.2%), acyclovir (84.2%) and IS (103.7%) from spiked plasma samples was consistent and reproducible. The bench top stability of valacyclovir and acyclovir was extensively evaluated in buffered and unbuffered plasma. It was successfully applied to a bioequivalence study in 41 healthy human subjects after oral administration of 1000 mg valacyclovir tablet formulation under fasting condition.     

Determination of eptifibatide concentration in human plasma utilizing the liquid chromatography–tandem mass spectrometry method

A sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed to determine the concentration of eptifibatide in human plasma. Following protein precipitation, the analyte was separated on a reversed-phase C₁₈ column. Acetonitrile:5 mM ammonium acetate:acetic acid (30:70:0.1, v/v/v) was used at a flow-rate of 0.5 mL/min with the isocratic mobile phase. An API 4000 tandem mass spectrometer equipped with a Turbo IonSpray ionization source was used as the detector and was operated in the positive ion mode. “Truncated” multiple reaction monitoring using the transition of m/z 832.6 → m/z 832.6 and m/z 931.3 → m/z 931.3 was performed to quantify eptifibatide and the internal standard (EPM-05), respectively. The method had a lower limit of quantification of 4.61 ng/mL for eptifibatide. The calibration curve was demonstrated to be linear over the concentration range of 4.61 ? 2770 ng/mL. The intra- and inter-day precisions were less than 10.5% for each QC level, and the inter-day relative errors were 2.0%, 5.6%, and 2.8% for 9.22, 184, and 2490 ng/mL, respectively. The validated method was successfully applied to the quantification of eptifibatide concentration in human plasma after intravenous (i.v.) administration of a 270-μg/kg bolus of eptifibatide and i.v. administration of eptifibatide at a constant rate of infusion of 2 μg/(kg min) for 18 h in order to evaluate the pharmacokinetics.