Simultaneous determination of paraquat and diquat in human plasma by HPLC-DAD: Its application in acute poisoning patients induced by these two herbicides

Background

Paraquat and diquat are widely used in agricultural production in many countries, which are very toxic to human beings. Paraquat can be detected in some diquat solution sold in the market. The blood concentration of paraquat or diquat is an important indicator for clinical diagnosis of paraquat or diquat poisoning. So, it is very meaningful to develop a method for simultaneous determination of paraquat and diquat in human plasma.

Objective

To develop and validate a HPLC‐DAD method for simultaneous determination of paraquat and diquat in human plasma and to apply it in the acute poisoning patients by these two herbicides.

Methods

Paraquat and diquat were simultaneously determined by HPLC‐DAD. The plasma was treated using Waters OASIS^® Column and then separated on a Thermo Hypersil GOLD (250 × 4.6 mm, 5 μm) Column with the mobile phase consisted of 75 mmol/L sodium heptane sulfonate (containing 0.1 mol/L phosphoric acid, pH 3.0) and acetonitrile (87:13, v:v) at a flow rate of 1.0 mL/min. The full‐wavelength scanning was 200‐400 nm, and the detection wavelength of paraquat and diquat was 257nm and 310nm, respectively. 120 and 30 plasma samples from patients with paraquat and diquat poisoning were collected and analyzed by the established method.

Results

The standard curve for paraquat and diquat ranged from 0.05 to 20 μg/mL, and the precision of LLOQ for paraquat was 16.49%, which was required to be less than 20%. The precision of other concentrations was less than 14.14%. The recovery of paraquat and diquat was 95.38%‐103.97% and 94.79%‐98.40%, respectively. The results showed that paraquat and diquat were stable under various storage conditions. 120 plasma samples of paraquat poisoning patients and 30 plasma samples of diquat poisoning patients were determined by the established method. The blood concentration of paraquat ranged from 0.10 to 20.62 μg/mL, with an average of 3.61 μg/mL, while for diquat, the concentration ranged from 0 to 26.59 μg/mL, with an average of 2.00 μg/mL. Among the diquat suspected poisoning samples, 5 samples were detected not only diquat but also paraquat, and 2 samples were detected only paraquat, no diquat.

Conclusion

The HPLC‐DAD method established in this study was high throughput, high sensitivity, simple operation, and wide linear ranges. It can be used for the screening analysis and quantitative detection of paraquat and diquat in acute poisoning patients, which can provide basis for the treatment and prognosis of these two herbicides poisoning patients.

Simultaneous Determination of Multiple Active Components from Bushen Pills and Application in a Pharmacokinetic Study in Rats

Bushen Pills (BSPs), as a traditional Chinese medicine (TCM), is widely used in clinic to enrich Yang, nourish Yin, stem essence, and strengthen kidneys. Two chromatographic methods, liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), were applied to analyze the multiple active components of BSPs in dosage form for quality evaluation and in rat plasma for pharmacokinetics study, respectively. Three active constituents of BSPs, including paeoniflorin (PF), berberine hydrochloride (BBR), and schizandrin (SCH), were simultaneously determined by the established LC-MS method with electrospray ionization (ESI) in positive selected ion monitoring (SIM) mode at m/z 503.1, 336.0, and 455.2. The contents of PF, BBR, and SCH were (6.112 ± 0.166) mg/g, (335.1 ± 14.95) μg/g, and (5.867 ± 0.136) μg/g in BSPs. On this basis, PF and BBR were selected as targeted analytes for the pharmacokinetic study of BSPs in rats. Memantine hydrochloride was used as an internal standard (IS), and the plasma samples were processed by liquid-liquid extraction with ethyl acetate. All the analytes were separated on a C₁₈ reversed phase column, eluted with a mobile phase consisting of acetonitrile-formic acid (0.01%) (25 : 75, v/v), and detected by ESI in the selected ion mode with multiple reaction monitoring (MRM). The target fragment ions were m/z 525.3 ⟶ 449.5 for PF, 336.2 ⟶ 320.2 for BBR, and 180.1 ⟶ 163.1 for IS. The linear ranges of PF and BBR were 5-500 ng/mL and 0.1-20 ng/mL with good linearity (r ² > 0.99). No obvious matrix effect was observed, and acceptable accuracy, precision, recovery, and stability were obtained. The proposed method has been successfully applied to the pharmacokinetic study of BSPs in rats after a single dose.

Pharmacokinetics and vasodilating effect study of beraprost sodium in healthy volunteers

Currently beraprost sodium (BPS) is widely proposed to ameliorate the symptoms caused by chronic arterial occlusive disease. The objective of this study is to investigate the BPS pharmacokinetic characteristics, its vasodilating effect and the relationship between plasma concentration vs response effect. 12 healthy Chinese volunteers (6 male, 6 female) were chosen to participate in a single center, random, and open design study. After overnight fasting, BPS (dose = 40μg) was administrated orally to each volunteer. The blood samples were collected at different time points (from 0 to 5 h after administration) and BPS concentration was analyzed by LC-MS/MS method. The vasodilating effect was evaluated by detecting the skin microcirculation blood flow of volunteers' fingers with laser Doppler fluxmetry. The C_max of BPS was (601.14 ± 214.81) pg/mL, the T_max was (0.58 ± 0.48) h, and AUC0-t was (1020.41±214.63) pg/mL•h. BPS exhibited significant vasodilating effect since the skin microcirculation blood flow increased definitely at 0.25, 0.5, and 0.75 h (all p<0.05) after drug administration, and a positive correlation was presented between the pharmacokinetics and the vasodilating effect, which would be beneficial for guiding BPS dosage in clinical.

Overview of the Chromatographic and Mass Spectrometry Analytical Methods for Determination of Lamivudine in Biological Fluids

Background:

Lamivudine was approved by Food and Drug Administration of the United States for the treatment of both HIV and HBV infection, which has been widely used as monotherapy or a component of combination therapy in clinics in many countries and nationalities.

Methods:

In this paper, the recent chromatographic and mass spectrometry analytical methods for the determination of lamivudine individually or combination with other drugs simultaneously were presented. These methods were widely applied in pharmacokinetics studies, bioequivalence studies, therapeutic drug monitoring studies, cell and animal experiments.

Conclusion:

The review paper might provide references for determining lamivudine in biological fluids, the intracorporal process of lamivudine, and the clinical practice by monitoring plasma concentration of lamivudine in the future.

LC-MS for Simultaneous Determination of Vancomycin and Teicoplanin in Patient Plasma and its Application to Therapeutic Drug Monitoring

Background:

Therapeutic drug monitoring is recommended for patients taking vancomycin and teicoplanin to ensure pharmaceutical efficacy and prevent toxicity. Only few studies were reported regarding the simultaneous determination of vancomycin and teicoplanin in human plasma.

Objective:

The study aimed at developing and validating a Liquid Chromatography-Mass Spectrometry (LC-MS) method for simultaneous determination and therapeutic drug monitoring of vancomycin and teicoplanin in patients with severe infection.

Method:

Plasma was processed by protein precipitation extraction. The analytes were separated on a C18 column by gradient elution with 0.1% formic acid and acetonitrile as mobile phase and measured by electrospray ionization source in positive selective ion monitoring mode at m/z 724.7 (vancomycin), 940.7 (teicoplanin) and 329.0 (bergenin). The plasma samples (104) were obtained from patients who were taking vancomycin or teicoplanin for further analysis.

Results:

The calibration curves were linear within the range of 0.25–40 µg/mL for vancomycin, and 0.5-40 µg/mL for teicoplanin. Either inter- or intra-day precision was less than 10.01 %. The extraction recoveries ranged from 89.99 to 94.29% for vancomycin and from 39.83 to 40.16 % for teicoplanin. Vancomycin and teicoplanin in plasma were stable at various storage conditions. The measured mean trough concentrations were 12.313 µg/mL for vancomycin and 8.765 µg/mL for teicoplanin.

Conclusion:

This method was successfully applied to therapeutic drug monitoring of vancomycin and teicoplanin in patients. It is with great clinic value for monitoring and predicting the individual response of patients under treatment.

Pharmacokinetic, metabolic profiling and elimination of brusatol in rats

Brusatol, a quassinoid isolated from the traditional Chinese medicine Brucea javanica, has been reported to be an inhibitor of Nrf2 pathway and has great potential to be developed into a novel chemotherapeutic adjuvant. However, the in vivo process of brusatol has not been comprehensively explained yet. Therefore, this paper focused on the pharmacokinetic metabolism and excretion of brusatol in rats using a simple and reproducible LC-MS/MS method. The results indicated that the plasma concentration of brusatol decreased rapidly; the average cumulative excretion rate in urine was 5.82% during 24 h, and 0.71% in bile during 12 h. High-resolution mass spectrometry was applied for the identification of metabolites; as a result, four metabolites were detected and the structure was tentatively deduced on the base of the MS² data, Compound Discoverer 2.0 and Mass Frontier 7.0 software. Hydroxylation, hydrolysis and glucuronidation were suggested as major metabolic pathways in vivo. The in vivo process and detection of metabolites of brusatol might improve the understanding of the mechanism of its anticancer effect and provide valuable information for its safety estimation, which will be essential to the new drug development.

Comparison of New Liquid Chromatography-Mass Spectrometry Method and Enzyme-Multiplied Immunoassay Technique for Routine Therapeutic Drug Monitoring of Vancomycin in Chinese Patients

BACKGROUND

Therapeutic drug monitoring of vancomycin is very valuable due to the good correlation between trough levels and clinical outcome. Therefore, it is important to accurately determine the concentration of vancomycin in patient plasma for adequate dose-adjustment. The objective of this study was to develop a new liquid chromatography-mass spectrometry (LC-MS) method for determination of vancomycin in patient plasma and compare the results with those obtained from enzyme-multiplied immunoassay technique (EMIT).

METHODS

After extraction by simple protein precipitation, vancomycin and bergenin (internal standard) were separated on a C18 column (150×4.6 mm, 5 µm) at 40°C by gradient elution with 0.1% formic acid and acetonitrile as the mobile phase and measured by electrospray ionization source in positive selective ion monitoring mode. Seventy-nine plasma samples from patients with severe infection were analyzed by enzyme-multiplied immunoassay technique and LC-MS method. MedCalc 15.2 software with Bland-Altman analysis and Passing-Bablok regression analysis was used for statistical analysis.

RESULTS

The weighted (1/x2) calibration curve of the validated LC-MS was linear within the concentration range of 0.25 - 40 µg/mL. The inter- and intra-day precisions (%RSD) were less than 10.0%. No significant matrix effect was observed in the relevant time ranges. Comparison of the two methods indicated that results of the LC-MS were close to that of EMIT with a correlation coefficient of 0.957. Upon Bland-Altman analysis, the bias amounted to 2.9 µg/mL (95% confidence intervals of -3.4 - 9.2 µg/mL).

CONCLUSIONS

The established LC-MS method and EMIT were both suitable for routine TDM of vancomycin.

[The efficacy and safety of insulin degludec versus insulin glargine in insulin-naive subjects with type 2 diabetes: results of a Chinese cohort from a multinational randomized controlled trial]

Objective: To compare the safety and efficacy of insulin degludec (IDeg) with those of insulin glargine (IGlar) in insulin-naive subjects with type 2 diabetes (T2DM). Methods: This was a 26-week, randomized, open-label, parallel-group, treat-to-target trial in 560 Chinese subjects with T2DM (men/women: 274/263, mean age 56 years, mean diabetes duration 7 years) inadequately controlled on oral antidiabetic drugs (OADs). Subjects were randomized 2∶1 to once-daily IDeg (373 subjects) or IGlar(187 subjects), both in combination with metformin. The primary endpoint was changes from baseline in glycosylated hemoglobin(HbA1c) after 26 weeks. Results: Mean HbA1c decreased from 8.2% in both groups to 6.9% in IDeg and 7.0% in IGlar, respectively. Estimated treatment difference (ETD) of IDeg-IGlar in change from baseline was -0.10% points (95%CI-0.25-0.05). The proportion of subjects achieving HbA1c<7.0% was 56.3%and 49.7% with IDeg and IGlar, respectively [estimated odds ratio of IDeg/IGlar: 1.26(95%CI 0.88-1.82)]. Numerically lower rateof overall confirmed hypoglycaemia and statistically significantly lower nocturnal confirmed hypoglycemia were associated with IDeg compared with IGlar, respectively [estimated rateratio of IDeg/IGlar 0.69(95%CI 0.46-1.03), and 0.43(95%CI 0.19-0.97)]. No differences in other safety parameters were found between the two groups. Conclusions: IDeg was non-inferior to IGlar in terms of glycaemic control, and was associated with a statistically significantly lower rate of nocturnal confirmed hypoglycaemia. IDeg is considered to be suitable for initiating insulin therapy in Chinese T2DM patients on OADs requiring intensified treatment. Clinical trail registration: Clinicaltrials.gov, NCT01849289.

Comparison of the docetaxel concentration in human plasma measured with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and a nanoparticle immunoassay and clinical applications of that assay

To determine the feasibility of using a nanoparticle immunoassay for clinical therapeutic drug monitoring (TDM) of docetaxel concentrations, a sensitive and simple method of liquid chromatography-tandem mass spectrometry (LC-MS/MS) was established to measure the docetaxel concentration in human plasma and the results of LC-MS/MS and the immunoassay were compared. Docetaxel and paclitaxel (the internal standard, or IS) in human plasma were extracted through protein precipitation, separated on a Diamonsil C18 column (150 mm × 4.6 mm, 5 μm), ionized with positive ions, and detected with LC-MS/MS in multi-reaction monitoring (MRM) mode. Plasma samples from 248 cancer patients were assayed with LC-MS/MS and a nanoparticle immunoassay. Data from the samples were analyzed with the statistical software SPSS and the software MedCalc. Results indicated that the calibration curve of the validated method of LC-MS/MS was linear over the range of 10-2,000 ng/mL, with an lowest limit of quantitation (LLOQ) of 10 ng/mL, and the intra- and inter- day precision and accuracy were both < ± 15%. Comparison of the two methods indicated that results of the LC-MS/MS were closely related to those of the nanoparticle immunoassay, with a correlation coefficient (R) of 0.965 and acceptable 95% confidence intervals (CI) of ‒ 231.7-331.1 ng/mL. Overall, the established method of LC-MC/MS and the nanoparticle immunoassay were both suitable for measurement of the docetaxel concentration in human plasma, and the immunoassay was far more cost-effective and better at clinical TDM of docetaxel in clinical practice.

Simple, rapid and highly sensitive HPLC method for measurement of Lamotrigine in human plasma and its clinical applications

Spikes in Lamotrigine concentrations levels and associated clinical toxicity may occur unpredictably. This study describes the development and validation of a simple, more rapid, highly sensitive and economical method for measuring Lamotrigine (LTG) concentration levels in human plasma using HPLC-UV and its clinical applications. Analyte from plasma was extracted with methanol (protein precipitation) and separated on the analytical column Diamonsil C₁₈ (150mm×4.6mm, 5μm) Waters-Milford, MA, United States. Mixture of 0.1% Trifluoroacetate and Methanol used as mobile phase in a 59:41 volume/volume mixture with an isocratic flow rate of 1.5 ml/min and wavelength was adjusted to 260nm. Standard curve of lamotrigine showed good linearity over the range of 1.0-50μg/mL (r²=0.9961) and LLOQ was 1.0μg/ml. The Specificity, Recovery, Accuracy, Stability, Robustness and RSDs for both intraday and interday precision were within acceptable limits. The highly sensitive HPLC assay for determination of LTG in human plasma was demonstrated, validated and applied in Therapeutic Drug Monitoring (TDM) of sixty seven epilepsy patients who were using LTG. The proposed method can be easily applied in routine Therapeutic monitoring of LTG, Besides TDM, stated method can be also very useful for Bioequivalence studies, Pharmacovigilance and Pharmacokinetics studies.

[Study on the expression of T, B lymphocyte antigen and platelet antibodies in patients with platelet transfusion refractoriness]

目的

探讨T、B淋巴细胞，血小板膜糖蛋白和血小板抗体在血小板输注无效中作用。

方法

选择41例临床确诊血小板输注无效患者为研究对象，以27例血小板输注有效患者为对照组，采用流式细胞术检测两组患者外周血细胞毒性T淋巴细胞（CD3 ⁺CD4⁻CD8⁺）、辅助性T淋巴细胞（CD3 ⁺ CD4⁺CD8⁻）、B淋巴细胞（CD19⁺）比例和血小板膜糖蛋白CD41а、CD61的表达，采用固相凝集法检测两组患者血清中的血小板抗体。

结果

与对照组比较，血小板输注无效组患者：①辅助性T细胞比例明显下降（36.60%对48.53%），细胞毒性T细胞比例显著增高（53.26%对44.02%），二者比值下降（0.85对1.31），差异均有统计学意义（P值均<0.05）；②B淋巴细胞比例差异无统计学意义（3.02%对2.85%，P=0.901）；③CD41а阳性细胞率[（88.10±12.75）%对（51.69±24.45）%，P=0.001]和CD61阳性细胞率[（88.36±12.31）%对（51.83±24.48）%，P<0.001]均显著升高；④血小板抗体阳性率显著增高（85.37%对14.82%，P<0.05）。

结论

细胞毒性T淋巴细胞的激活、辅助性T细胞的抑制、血小板膜糖蛋白CD41а和CD61的表达以及血小板抗体的产生均在血小板输注无效的发生过程中发挥重要作用。

Association between adiponectin gene T45G polymorphism and nonalcoholic fatty liver disease risk: a meta-analysis

Numerous epidemiological investigations have evaluated the association between adiponectin gene T45G polymorphism and risk of nonalcoholic fatty liver disease (NAFLD). However, the results of these studies have proven to be inconsistent. Therefore, we conducted a meta-analysis to obtain a more accurate estimation of this association. Published articles were retrieved from PubMed and Web of Science databases and pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using fixed- or random-effect models. Five case-control studies incorporating 597 cases and 701 controls were included in this meta-analysis. No association between adiponectin gene T45G polymorphism and NAFLD was established (TT vs GG: OR = 0.83, 95%CI = 0.37-1.86; TG vs GG: OR = 0.76, 95%CI = 0.33-1.79; dominant model: OR = 0.83, 95%CI = 0.37-1.84; recessive model: OR = 1.10, 95%CI = 0.69-1.76). Moreover, in a subgroup analysis, no significant correlation was found among Asian subjects. In conclusion, the T45G polymorphism of the adiponectin gene may not constitute an NAFLD risk factor. However, this needs to be further validated in single large well-designed future studies.

Changes and clinical significance of serum vaspin levels in patients with type 2 diabetes

We investigated serum visceral adipose tissue-derived serpin (vaspin) levels in patients with normal glucose regulation and recently diagnosed type 2 diabetes (T2DM) and explored the association between vaspin and body mass index, age, gender, glucose, lipid metabolism, and insulin sensitivity. Fasting serum vaspin levels in 66 patients with T2DM and 48 normal subjects were detected using enzyme-linked immunosorbent assay. We found that serum vaspin levels in the DM group were 0.65 ± 0.13 mg/L in non-obese patients and 1.13 ± 0.25 mg/L in obese patients. Serum vaspin levels in the control group were 0.38 ± 0.18 mg/L in non-obese patients and 0.95 ± 0.11 mg/L in obese patients. Average serum vaspin levels were significantly higher in obese patients than in non-obese patients in both the DM group and control group. In the DM group, the serum vaspin level was 0.76 ± 0.22 mg/L in males and 0.92 ± 0.35 mg/L in females. In the control group, the serum vaspin level was 0.48 ± 0.14 mg/L in males and 1.05 ± 0.21 mg/L in females. Association analysis showed that serum vaspin levels were significantly associated with body mass index, waist-to-rip ratio (WHR), fat percentage, triglyceride, fasting plasma insulin, and insulin sensitivity index. Stepwise multiple regression analysis showed that gender, insulin sensitivity index, and WHR were the most significant independent factors affecting vaspin. Therefore, serum vaspin levels were significantly elevated in obese people and were independently associated with WHR, gender, and index sensitivity index.

The use of transcallosal-interforniceal approach for microsurgical removal of the third ventricle tumors

AIM

The third ventricle is located deep in the brain and is adjacent to important neurovascular structures. This makes tumor resection in this region difficult and causes more postoperative complications than surgeries in other regions of the brain. The objective of this study was to investigate the feasibility and clinical effects of transcallosal-interforniceal approach for microsurgical removal of the third ventricle tumors.

METHODS

After preoperative evaluation, 23 patients with the third ventricle tumors were microsurgically operated using the transcallosal-interforniceal approach.

RESULTS

Of these 23 patients, 12 (52.2%) underwent total excision, 9 (39.1%) had subtotal resection, and the remaining 2 (8.7%) underwent partial excision. After surgery, the following complications were observed: diabetes insipidus (11 patients), hemorrhages of the upper digestive tract (2 patients), central fever (1 patient), and memory impairment (1 patient). No mortality in the perioperative period was reported.

CONCLUSION

The surgical procedure using the transcallosal-interforniceal approach is direct and provides good surgical field exposure and fewer post operational compilations. This approach should be considered as the method of choice for surgical removal of the third ventricle tumors.

Metabolism and disposition of tribendimidine and its metabolites in healthy Chinese volunteers

Background: Tribendimidine is a new anthelmintic agent synthesized by Chinese scientists. It is a broad spectrum agent with high activity against parasites. However, its disposition and metabolism remain unknown.

Objective: To investigate the metabolism, disposition, and metabolites of tribendimidine in healthy human volunteers.

Methods: Twelve healthy Chinese volunteers were chosen after clinical assessment of health status and laboratory tests. They received single oral doses of tribendimidine 400mg enteric-coated tablets. Blood and urine samples were collected at scheduled timepoints. Samples were qualitatively and quantitatively analyzed by liquid chromatography-mass spectrometric (LC-MS) and high performance liquid chromatography (HPLC) methods, respectively.

Results: Tribendimidine was rapidly and completely broken down to p-(1-dimethylamino ethylimino) aniline (dADT) and terephthalaldehyde (TPAL). Furthermore, dADT was partially transformed to acetylated dADT, and TPAL completely transformed to terephalic acid (TPAC). The main pharmacokinetic parameters (± SD) of dADT were as follows: elimination half life (t_1/2) 4.74 ± 1.80 h; elimination rate constant (K_e) 0.16 ± 0.06 h⁻¹; apparent volume of distribution (Vd/F) 12.23 ± 8.69L • kg⁻¹; apparent total clearance of the drug from plasma (CL/F) 1.63 ± 0.58L • h⁻¹ • kg⁻¹; area under the plasma concentration-time curve (AUC) from time 0 to time 24 hours (AUC₂₄) 4.29 ± 1.88 μg • mL⁻¹ • h; AUC from time zero to infinity (AUC_∞) 4.45 ± 1.81 μg • mL⁻¹ • h; maximum plasma drug concentration (C_max) 0.64 ± 0.27 μg • mL⁻¹; and time to C_max (t_max) 4.20 ± 0.71 h. A total of 35.28% dADT and 28.50% TPAC were excreted through the urine within 24 hours after tribendimidine administration.

Conclusion: These results reveal the disposition, metabolism, and main metabolites of tribendimidine in healthy Chinese volunteers.

Determinations of mifepristone and its metabolites and their pharmacokinetics in healthy female Chinese subjects

The aim of this study is to establish an HPLC method for simultaneous determinations of mifepristone and its metabolites, mono-demethylated mifepristone, di-demethylated mifepristone and C-hydroxylated mifepristone in plasma and to evaluate the pharmacokinetic characteristics of mifepristone tablet. Twenty healthy female Chinese subjects were recruited and a series of blood samples were collected before and after 0.25, 0.5, 1.0, 1.5, 2.0, 4.0, 8.0, 12.0, 24.0, 48.0, 72.0 and 96.0 hours administration by a single oral dose of 75 mg mifepristone tablet. Mifepristone and its three metabolites were extracted from plasma using ethyl acetate and determined by high performance liquid chromatography. The main pharmacokinetic parameters of mifepristone and its metabolites, including Cmax, tmax, MRT, t(1/2), V, CL, AUC(0-96 h) and AUC(0-infinity), were calculated by Drug and Statistical Software Version 2.0. The simple, accurate and stable method allows the sensitive determinations of mifepristone and its metabolites in human plasma up to 4 days after oral administration of 75 mg mifepristone tablet and the clinical applications of their pharmacokinetic studies.

A tunable radio-frequency magnetic probe

A tunable center-tapped transformer is proposed to increase the output of a rf magnetic probe and improve the signal-to-noise ratio. The tuning is implemented by a variable capacitor connected parallel with the primary winding of the tunable center-tapped transformer. Undesirable common-to-differential conversion is reduced by installing a compensating capacitor. In addition, a planar Faraday shield is installed between the windings of the transformer to further suppress the electrostatic coupling. It is found that tuning the variable capacitor can result in a resonance in the output voltage of the rf magnetic probe. The largest output voltage, achieved with the tunable magnetic probe under the optimal condition, is higher than that with a conventional one by an order of magnitude. Effects of the compensating capacitance on the common-mode output voltage are studied and discussed. Influences of parameters such as cable length, the coupling coefficient, and the step-up ratio of the transformer on the output voltage are also presented. Analytical derivations and numerical calculations based on the equivalent circuit are performed to elucidate the characteristics of the differential mode.

Comparison of different pharmacodynamic models for pharmacokinetic-pharmacodynamic (PK-PD) modeling of carvedilol

The paper is aimed to investigate the pharmacokinetic (PK) and the pharmacodynamic (PD) properties of carvedilol using indirect response and effect-compartment link models, and compare the fitness of PK-PD models. Twenty male healthy Chinese volunteers received a single oral dose of 20 mg of carvedilol. The plasma concentrations of carvedilol were determined by reversed-phase HPLC method with fluorescence detection, and the pharmacokinetic parameters were calculated by DAS2.0. The mean arterial blood pressure was measured and the pharmacodynamics of carvedilol was characterized by tail-cuff manometry. The main pharmacokinetic parameters of carvedilol were as follows, t1/2 (4.56 +/- 2.56) h, Cmax (46.29 +/- 21.07) ng x mL(-1), AUC(0-infinity) (173.76 +/- 87.36) ng x mL(-1) x h. The estimated Kin was (0.41 +/- 0.31)% h(-1), Kout was (0.40 +/- 0.26) h(-1), the IC50 value was (24.40 +/- 21.10) ng x mL(-1) and the area under the effect curve (AUE) was (3.82 +/- 1.46)% h for the indirect response PD model. The Ke0 was (0.35 +/- 0.27) h(-1), the EC50 was (24.30 +/- 24.30) ng x mL(-1), and the AUE was (5.65 +/- 2.54)% h for the effect-compartment model. The HPLC method can be used for the pharmacokinetic study of carvedilol. The proposed effect-compartment link model provided more appropriate and better-fitting PK/PD characteristics than the indirect response model in Chinese healthy volunteers according to Akaike's information criterion values.

Determination of sodium cromoglycate in human plasma by liquid chromatography with tandem mass

A sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated for the determination of sodium cromoglycate (SCG) in human plasma after a nasal dose of 10.4 mg sodium cromoglycate nasal spray, using pravastatin sodium as the internal standard. The method was validated over a linear range of 0.300-20.0 ng/mL. SCG and I.S. were extracted from 1.0 mL of heparinized plasma by C(18) solid-phase extraction cartridges using methanol as eluting solvent. The dried residue was reconstituted with 100 microL of mobile phase, and 10 microL was injected onto the LC-MS/MS system. Chromatographic separation was achieved on a C(18) column (250 x 4.6 mm i.d., 5 microm particle size) with a mobile phase of methanol-acetonitrile-water (containing 2 mmol/L ammonium acetate; 42.5:42.5:15, v/v/v) at a flow rate of 0.4 mL/min. The analytes were detected with a triple quad LC-MS/MS using ESI with positive ionization. Ions monitored in the multiple reaction monitoring mode were m/z 469.0 (precursor ion) to m/z 245.0 (product ion) for SCG and m/z 447.2 (precursor ion) to m/z327.1 (product ion) for pravastatin sodium (internal standard) The average recovery of SCG from human plasma was 94.88% and the lower limit of quantitation was 0.3 ng/mL. Results from a 3-day validation study demonstrated excellent precision and accuracy across the calibration range of 0.3-20 ng/mL. The method was successfully applied to the pharmacokinetic study of SCG in healthy Chinese volunteers.

[HPLC-MS/MS method for determination of sodium cromoglycate concentration in human plasma and its pharmacokinetics]

The study established an HPLC-MS/MS method for determining the concentrations of sodium cromoglycate in human plasma and evaluated the pharmacokinetics of nasal drops and nasal spray. A C18 column was used to separate sodium cromoglycate in plasma with a mobile phase of a mixture of ammonium-methanol (involves 50% acetonitrile) (15:85) at a flow rate of 0.4 mL x min(-1). Electronic spray ionization (ESI) and multiple-reaction monitoring (MRM) were used for the determination of sodium cromoglycate in human plasma. The linear range of the standard curve of sodium cromoglycate was from 0.3 to 20 ng x mL(-1), and the minimum concentration of detection was 0.3 ng x mL(-1). The extraction recovery was more than 94.1%, intra-day and inter-day RSD were less than 14.3%. After a single dose of sodium cromoglycate, the main pharmacokinetic parameters of nasal spray and nasal drops were as follows, T(1/2)(1.82 +/- 0.54) h, (1.59 +/- 0.52) h; Tmax (0.47 +/- 0.12) h, (0.44 +/- 0.15) h; Cmax, (9.79 +/- 4.66) ng x mL(-1), (10.88 +/- 4.05) ng x mL(-1); AUC(0-5 h)(11.52 +/- 3.46) ng x mL(-1) x h x h, (12.63 +/- 4.23) ng x mL(-1) x h, Fr(93.6 +/- 13.8)%. The method is sensitive, rapid and accurate. It is suitable for therapeutic drug monitoring and human pharmacokinetic study of sodium cromoglycate.

Determination and pharmacokinetic study of norcantharidin in human serum by HPLC-MS/MS method

A sensitive, simple and selective high-performance liquid chromatography-tandem mass spectrometry method was developed and applied to the determination of norcantharidin concentration in human serum. Norcantharidin (NCTD) and cyclophosphamide (IS) in serum were extracted with acetone, separated on a C18 reversed-phase column, gradiently eluted with a mobile phase of acetonitrile-water containing 2 mm ammonium acetate and 0.1% formic acid (pH 3), ionized by positive ion pneumatically assisted electrospray and detected in the multi-reaction monitoring mode using precursor-->product ions of m/z 169.3-->123.1 for NCTD and 261.2-->140.2 for IS, respectively. The linear range of the calibration curve for NCTD was 2.5-50 ng/mL, with a lowest limit of quantification of 2.5 ng/mL, and the intra/inter-day RSD was less than 10%. The method was suitable for determination of low NCTD concentration in human serum after therapeutic oral doses, and has been successfully used for pharmacokinetic studies in healthy Chinese volunteers.