In silico, in vitro and in vivo metabolite identification of brexpiprazole using ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry.

RATIONALE: Brexpiprazole is a novel serotonin-dopamine activity modulator approved by the USFDA in July 2015 for the treatment of schizophrenia and as an adjunctive therapy with other antidepressants for major depressive disorder in adults. However, limited numbers of metabolites are reported in the literature for brexpiprazole. Our prime intent behind this study is to revisit metabolite profiling of brexpiprazole and to identify and characterize all possible in vitro and in vivo metabolites. METHODS: Firstly, the site of metabolism for brexpiprazole was predicted by a Xenosite web predictor model. Secondly, in vitro metabolite profiling was performed by incubating the drug individually with rat liver microsomes, human liver microsomes and rat S9 fraction at 37°C for 1 h in incubator shaker. Finally, for in vivo metabolite identification, a 50 mg kg-1 dose of brexpiprazole was administered to male Sprague-Dawley rats and the presence of various metabolites was confirmed in rat plasma, urine and feces. RESULTS: The predicted atomic site of metabolism was obtained as a color gradient by the Xenosite web predictor tool and, from this study, probable metabolites were listed. In total, 14 phase I and 2 phase II metabolites were identified and characterized in the in vitro and in vivo matrices using ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UHPLC/QTOF-MS/MS). The majority of metabolites were found in the sample incubated with human liver microsomes and in rat urine, while in the other matrices only a few metabolites were detected. CONCLUSIONS: All the 16 metabolites were identified and characterized using UHPLC/QTOF-MS/MS. The study revealed that brexpiprazole is metabolized via hydroxylation, glucuronidation, S-oxidation, N-oxidation, dioxidation, oxidative deamination, N-dealkylation, etc.

[Clinical and biochemical aspects of pathogenesis of urolithiasis].

AIM: To investigate the role of infection in the pathogenesis of urolithiasis using chromatography mass spectrometry analysis. MATERIALS AND METHODS: The study analyzed clinical and laboratory data of 316 urolithiasis patients hospitalized between February 2005 and January 2015. All patients underwent a comprehensive clinical examination, including laboratory tests (hematological and biochemical blood tests, clinical and bacteriological tests of urine) and chromatography mass spectrometry analysis urine and blood. The laboratory testing was carried out both during the patients hospital stay and outpatient follow-up. RESULTS: We analyzed the biological material for the presence of characteristic ions. Urine samples of 316 urolithiasis patients were found to contain activators of "cooperative sensitivity." Moreover, there was a significant increase in the concentration of signaling compounds of the "cooperative sensitivity" of microorganisms in patients with complicated urolithiasis in comparison with the control indices (lactones-0.006 plus/minus 0.0004 mmol/L, normal values less than 0.002, quinolones 0.004 plus/minus 0.0003 mmol/l, normal values - less than 0.002 and furan esters - 0.005 plus/minus 0.0004, normal values less than 0.002). Threshold values of the activators of "cooperative sensitivity" demonstrated the readiness of the microbial community to initiate an inflammatory process. The presence of activators such as lactones, quinolones and furan esters in the samples of urolithiasis patients predisposes to the activation of pathogenic genes in a large group of microorganisms, including gram positive and gram negative species. DISCUSSION: In our opinion, to improve the quality of diagnostic, treatment and preventive measures in patients with different types of stone formation, it is advisable to use chromatography mass spectrometry analysis, which allows determination of priority clinical and laboratory indicators. CONCLUSION: The data on the role of infection in the pathogenesis of urolithiasis obtained by chromatographic methods suggest the possibility of using the indicators of the activators of the "cooperative sensitivity" of microbes in patients with various forms of urolithiasis to assess the disease severity.

Determination of a novel nonfluorinated quinolone, nemonoxacin, in human feces and its glucuronide conjugate in human urine and feces by high-performance liquid chromatography-triple quadrupole mass spectrometry.

Three methods were developed and validated for determination of nemonoxacin in human feces and its major metabolite, nemonoxacin acyl-ß- d-glucuronide, in human urine and feces. Nemonoxacin was extracted by liquid-liquid extraction in feces homogenate samples and nemonoxacin acyl-ß- d-glucuronide by a solid-phase extraction procedure for pretreatment of both urine and feces homogenate sample. Separation was performed on a C18 reversed-phase column under isocratic elution with the mobile phase consisting of acetonitrile and 0.1% formic acid. Both analytes were determined by liquid chromatography-tandem mass spectrometry with positive electrospray ionization in selected reaction monitoring mode and gatifloxacin as the internal standard. The lower limit of quantitation (LLOQ) of nemonoxacin in feces was 0.12 µg/g and the calibration curve was linear in the concentration range of 0.12-48.00 µg/g. The LLOQ of the metabolite was 0.0010 µg/mL and 0.03 µg/g in urine and feces matrices, while the linear range was 0.0010-0.2000 µg/mL and 0.03-3.00 µg/g, respectively. Validation included selectivity, accuracy, precision, linearity, recovery, matrix effect, carryover, dilution integrity and stability, indicating that the methods can quantify the corresponding analytes with excellent reliability. The validated methods were successfully applied to an absolute bioavailability clinical study of nemonoxacin malate capsule.

A rapid and sensitive resonance Rayleigh scattering spectra method for the determination of quinolones in human urine and pharmaceutical preparation.

A new method based on resonance Rayleigh scattering (RRS) was proposed for the determination of quinolones (QNS) at the nanogram level. In pH 3.3-4.4 Britton-Robinson buffer medium, quinolones such as ciprofloxacin, pipemidic acid (PIP), lomefloxacin (LOM), norfloxacin (NOR) and sarafloxacin (SAR) were protonated and reacted with methyl orange (MO) to form an ion-pair complex, which then further formed a six-membered ring chelate with Pd(II). As a result, new RRS spectra appeared and the RRS intensities were enhanced greatly. RRS spectral characteristics of the MO-QNS-Pd(II) systems, the optimum conditions for the reaction, and the influencing factors were investigated. Under optimum conditions, the scattering intensity (∆I) increments were directly proportional to the concentration of QNS with in certain ranges. The method had high sensitivity, and the detection limits (3σ) ranged from 6.8 to 12.6 ng/mL. The proposed method had been successfully applied for the determination of QNS in pharmaceutical formulations and human urine samples. In addition, the mechanism of the reaction system was discussed based on IR, absorption and fluorescence spectral studies. The reasons for the enhancement of scattering spectra were discussed in terms of fluorescence-scattering resonance energy transfer, hydrophobicity and molecular size.

Metabolism and pharmacokinetics of indacaterol in humans.

The metabolism, pharmacokinetics, and excretion of [(14)C]indacaterol were investigated in healthy male subjects. Although indacaterol is administered to patients via inhalation, the dose in this study was administered orally. This was done to avoid the complications and concerns associated with the administration of a radiolabeled compound via the inhalation route. The submilligram doses administered in this study made metabolite identification and structural elucidation by mass spectrometry especially challenging. In serum, the mean t(max), C(max), and AUC(0-last) values were 1.75 h, 0.47 ng/ml, and 1.81 ng · h/ml for indacaterol and 2.5 h, 1.4 ngEq/ml, and 27.2 ngEq · h/ml for total radioactivity. Unmodified indacaterol was the most abundant drug-related compound in the serum, contributing 30% to the total radioactivity in the AUC(0-24h) pools, whereas monohydroxylated indacaterol (P26.9), the glucuronide conjugate of P26.9 (P19), and the 8-O-glucuronide conjugate of indacaterol (P37) were the most abundant metabolites, with each contributing 4 to 13%. In addition, the N-glucuronide (2-amino) conjugate (P37.7) and two metabolites (P38.2 and P39) that resulted from the cleavage about the aminoethanol group linking the hydroxyquinolinone and diethylindane moieties had a combined contribution of 12.5%. For all four subjects in the study, ≥90% of the radioactivity dose was recovered in the excreta (85% in feces and 10% in urine, mean values). In feces, unmodified indacaterol and metabolite P26.9 were the most abundant drug-related compounds (54 and 17% of the dose, respectively). In urine, unmodified indacaterol accounted for ∼0.3% of the dose, with no single metabolite accounting for >1.3%.

A liquid chromatography-tandem mass spectrometry assay for the determination of nemonoxacin (TG-873870), a novel nonfluorinated quinolone, in human plasma and urine and its application to a single-dose pharmacokinetic study in healthy Chinese volunteers.

Nemonoxacin (TG-873870) is a novel C-8-methoxy nonfluorinated quinolone with higher activity than ciprofloxacin, levofloxacin and moxifloxacin against Gram-positive pathogens including methicillin-susceptible or methicillin-resistant Staphylococcus aureus and Streptococcus pneumoniae with various resistant phenotypes. A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated to determine the concentration of nemonoxacin in human plasma and urine. Protein precipitation and liquid-liquid extraction were employed for plasma and urine sample preparations, respectively, and extract was then injected into the system. Separation was performed on a C(18) reversed-phase column using acetonitrile-0.1% formic acid as a mobile phase. Both analyte and internal standard (gatifloxacin) were determined using electrospray ionization and the MS data acquisition via the selected reaction monitoring in positive-ion mode. The lower limit of quantification was 5 ng/mL and the calibration curves were linear in the concentration range of 5-1000 ng/mL. The accuracy, precision, selectivity, linearity, recovery, matrix effect and stability were validated for TG-873870 in human plasma and urine. The method was successfully applied to a pharmacokinetic study enrolling 12 healthy Chinese volunteers administered nemonoxacin malate capsules.

Liquid chromatographic determination of quinolones in water and human urine samples after microextraction by packed sorbent.

A method for the simultaneous determination of quinolones in water and urine samples by microextraction in a sorbent-packed syringe (MEPS) with LC is described. MEPS is a new miniaturized SPE technique that can be used with chromatographic instruments without any modifications. In MEPS, approximately 1 mg of the solid packing material is inserted into a syringe (100-250 microL) as a plug. Sample preparation takes place on the packed bed. The new method is promising, easy to use, economical, and rapid. The determination of quinolones in groundwater and urine was performed using MEPS as a sample preparation method with LC-UV determination. Four quinolone antibiotics--enrofloxacin, enoxacin, danofloxacin, and nalidixic acid--in groundwater and urine samples were used as analytes. The extraction recovery was found to be between 64.9 and 98.9%. The results showed high correlation coefficients (R2 > 0.992) for all of the analytes within the calibration range. The LOQ was between 0.091 and 0.315 ng/mL.

Enantiomeric resolution of quinolones on crown ether CSP: Thermodynamics, chiral discrimination mechanism and application in biological samples.

The enantiomers of quinolone racemates were resolved using chiral crown ether within 8 min. Thermodynamics data and modeling results were used to determine chiral recognition mechanism. The column used was (+)-Crownpack column (250 mm × 4.6 mm, 5 µm) with three mobile phases I: ACN:Water (80:20) + 10 mM H2SO4 and 10 mM CH3COONH4, II: ACN:Water (80:20) + 20 mM perchloric acid and III: EtOH:Water (80:20) + 20 mM perchloric acid. The flow rate of the mobile phases was 1.0 mL/min with UV detection at different wavelengths. The ranges of retention (k), separation (α), and resolution (Rs) factors were 1.00-5.40, 1.37-2.00 and 1.50-3.30. The tailing factor was 1.o for all peaks with 900-2325 as the number of theoretical plates were 8.0-10.0 and 32.4-22.1 µg. The difference in enthalpy, entropy and free energy varied in the range of -0.350 to -0.024, 18.74 × 10-4 to 3.94 × 10-4 and -0.918 to -0.143, respectively. The thermodynamic and docking results showed chiral discrimination due to physical forces of amnio group cations penetration into the chiral cavity of the chiral selector following hydrogen bindings. The binding energy of S-enantiomers was higher than R-enantiomers; confirming stronger binding of S-enantiomers with CSP than R-enantiomers. The described chiral-HPLC method was used for the analysis of the quinolone enantiomers in urine samples and the results were quite satisfactory. Therefore, the reported method may be used for the enantiomeric separation of quinolone enantiomers in urine samples.

A capillary zone electrophoretic method for simultaneous determination of seven drugs in pharmaceuticals and in human urine.

A simple, sensitive, and novel method has been developed and validated for the separation and simultaneous quantitation of seven structurally different drugs-pipemidic acid and ofloxacin quinolone antibiotics, pseudoephedrine decongestant, piroxicam anti-inflammatory, thiamin, pyridoxine, and cobalamin-in a mixture by capillary zone electrophoresis. Factors affecting the separation were pH, concentration of buffer, and applied voltage. Separation was carried out in < 9 min with a 50 mM sodium tetraborate buffer, pH 10, and an applied voltage of 30 kV in an uncoated silica capillary tube. The carrier electrolyte gave baseline separation with good resolution, reproducibility, and accuracy. Calibration plots were linear over at least three orders of magnitude of analyte concentrations, and the lower LODs were within the range of 1-5 microg/mL. Detection was performed by UV absorbance at 230 nm. The method was validated for the analysis of drugs in pharmaceutical preparations and in urine samples with RSD of 0.5-2.4% and recovery of > 99%.

Determination of Quinolone Antibiotic Residues in Human Serum and Urine Using High-Performance Liquid Chromatography/Tandem Mass Spectrometry.

Quinolone antibiotic residues may pose potential threat to human health. A rapid and sensitive method was developed for the determination of quinolone residues in human serum and urine. After solid phase extraction (SPE) process, eight quinolone residues were analyzed by high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) using ciprofloxacin-d8 as the internal standard. The relative standard deviation of intra-day and inter-day precision for the eight quinolones were less than 7.52% and the accuracies ranged from 95.8% to 103% in human serum, and from 94.1% to 104% in human urine. The extraction recoveries for the eight quinolones varied from 80.2% to 113% in human serum and 83.4% to 117% in human urine. The limit of detection for the eight quinolones was 0.50-1.00 ng/mL. Quinolone antibiotic residues in human serum and urine from 12 volunteers were successfully analyzed with the validated method. The SPE-HPLC-MS/MS method was useful for accurate determination of quinolone antibiotic residues in human body.

Population Pharmacokinetics Study of Nemonoxacin Among Chinese Patients With Moderate Hepatic Impairment.

PURPOSE: Nemonoxacin is a novel C-8-methoxy nonfluorinated quinolone that has been approved for the treatment of community-acquired pneumonia (CAP) in adults. The goals of this study were to evaluate the pharmacokinetic (PK) and population PK parameters of nemonoxacin and to provide the appropriate dose adjustment recommendations for patients with hepatic impairment. METHODS: An open-label, single-dose, parallel group (moderate hepatic impairment group and healthy control group) PK study of nemonoxacin was conducted. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to detect the unchanged nemonoxacin concentration in blood and urine samples. The nonlinear mixed effects modeling tool NONMEN (version 7.3) was used to conduct the population PK analysis. The paired-t test was conducted to compare the PK parameters of the hepatic impairment group and the healthy control group by SPSS (Version 17.0). FINDINGS: Ten subjects for each group were enrolled into the PK study. The PK parameters as well as the plasma concentration-time and logarithmic concentration-time profiles after taking a 500-mg single dose of nemonoxacin showed few differences between the two groups (P > 0.05). The mean areas under the plasma concentration vs. time curve from 0 to 72 h (AUC0-72 h) of the moderate hepatic impairment group and the healthy control group in the nemonoxacin PK study were 58.50 (17.30) mg·h/mL and 49.74 (10.16) mg·h/mL, respectively, giving a mean (SD) AUC0-72 h ratio of 1.15 (0.42) with a 90% CI of 0.91-1.39. A 3- compartment model was considered to be the best model for the data, especially in fitting the plasma point at low drug concentrations. Covariate analysis indicated that weight affected CL/F, V1/F, and V3/F and that eGFR only affected CL/F in the power function model, while gender affected V3/F in the linear model by forward selection and backward deletion. IMPLICATIONS: The population PK parameters of nemonoxacin were evaluated in patients with hepatic impairment. The hepatic function did not have a significant impact on the PK parameters of nemonxacin, but renal function was a meaningful covariate that is consistent with its PK characteristics. In this study, nemonoxacin was well tolerated in the patients with moderate hepatic impairment as well as in the healthy subjects. Based on these data, it is not necessary to consider dose adjustment of nemonoxacin in patients with mild or moderate hepatic impairment. ClinicalTrials.gov identifier: NCT02604498.

Recognition mechanism of water-compatible molecularly imprinted solid-phase extraction and determination of nine quinolones in urine by high performance liquid chromatography.

Novel water-compatible molecularly imprinted polymers (MIPs) were synthesized in methanol-water systems with ofloxacin as templates and methacryclic acid as functional monomers. The MIPs were used as a special sorbent for the selective solid-phase extraction (SPE) of nine quinolones from urine samples, showing high affinity to the quinolones in aqueous environment. Its molecular recognition mechanisms were investigated by the molecular simulation and the experimental validation with UV and infrared spectrogram as well as (1)H NMR. Binding capability and chromatographic characteristic were also evaluated. By using the water-compatible MIPs as SPE sorbents, the nine quinolones can be selectively extracted and enriched, while all matrices interferences were eliminated simultaneously. Under the optimal conditions of SPE and high performance liquid chromatography (HPLC), the good linearity of the method was obtained in a range of 0.05-30microg/mL with the correlation coefficient of >0.999 and the relative standard division of 2.0-7.4%. The detection limits (s/n=3) were in a range of 0.036-0.10microg/mL. The proposed method was successfully applied for the selective extraction and separation of the studied quinolones in urine samples.

Pharmacokinetics, Excretion, and Mass Balance of [14 C]-Batefenterol Following a Single Microtracer Intravenous Dose (Concomitant to an Inhaled Dose) or Oral Dose of Batefenterol in Healthy Men.

Inhaled batefenterol is an investigational bifunctional molecule for the treatment of chronic obstructive pulmonary disease. The excretion balance and pharmacokinetics of batefenterol using [14 C]-radiolabeled drug administered orally and as intravenous (IV) infusion were assessed. In this 2-period, open-label study, 6 healthy male subjects received a single IV microtracer 1-hour infusion of 4 µg [14 C]-batefenterol concomitant with inhaled nonradiolabeled batefenterol (1200 µg) followed by oral [14 C]-batefenterol (200 µg) in period 2 after a 14-day washout. The primary end points included: the area under the concentration-time curve from time zero to last time of quantifiable concentration (AUC0-t ); maximum observed concentration (Cmax ); and time of occurrence of maximum observed concentration. Following IV administration, the geometric mean AUC0-t of [14 C]-batefenterol was 121.9 pgEq • h/mL; maximum observed concentration and time of occurrence of maximum observed concentration were 92.7 pgEq/mL and 0.8 hours, respectively; absolute oral bioavailability was 0.012%. The mean AUC0-t ratio indicated that [14 C]-batefenterol accounted for 85% of total circulating radioactivity in the plasma initially and declined rapidly following IV administration, but only ∼0.2% of total circulating radioactivity following oral administration. Cumulative mean recovery of total radioactive [14 C]-batefenterol in urine and feces was 6.31% and 77.6%, respectively. Overall, batefenterol exhibited low systemic bioavailability after inhaled and oral administration, and high fecal excretion and low urinary excretion following IV and oral administration.

Determination of ulifloxacin by terbium-sensitized fluorescence with second-order scattering and its applications.

This paper reports the determination of ulifloxacin (UFX) by terbium-sensitized fluorescence using a second-order scattering method. UFX and Tb(III) ion form a fluorescence complex in aqueous solution, and its maximum excitation and emission wavelengths are located at 273 and 545 nm, respectively. In optimum conditions, the relative intensity at 545 nm has a linear relationship to the concentration of UFX in the range of 2.0 x 10(-8) - 1.0 x 10(-5) mol L(-1) and the detection limit is 3.9 x 10(-9) mol L(-1). The proposed method was applied to the determination of UFX in spiked human serum and urine satisfactorily. The luminescence property of UFX is also discussed by comparing with norfloxacin (NFLX) and ofloxacin (OFLX).

A sensitive assay for ZYAN1 in human whole blood and urine utilizing positive LC-MS/MS electrospray ionization.

AIM: A sensitive LC-MS/MS method was developed and validated for estimation of ZYAN1 in human blood/urine. METHODS: An analog internal standard IOX2 along with ZYAN1 was quantified using selective reaction monitoring in positive mode. The chromatographic separation was performed by gradient elution with C18 analytical column (3 µm, 50 mm × 2.0 mm) with 4-min run time using an acidified mobile phase consisting of ammonium formate and acetonitrile. Protein precipitation enabled extraction of analytes from diluted blood/urine. RESULTS: Calibration curve of ZYAN1 was linear (2-5000 ng/ml). The recovery of ZYAN1 and IOX2 was between 87 and 104%. Interday and intraday accuracy and precision was found well within the acceptance criteria. CONCLUSION: The validated assay was applied for clinical pharmacokinetics of ZYAN1 in healthy volunteers.

Trace levels of pyrroloquinoline quinone in human and rat samples detected by gas chromatography/mass spectrometry.

A detailed procedure for the assay of free pyrroloquinoline quinone (PQQ) in human and rat samples by gas chromatography/mass spectrometry (GC/MS) has been established with stable-isotopic PQQ as internal standard. PQQ was extracted from the samples, after addition of the internal standard, with butanol under acid conditions and with Sep-Pak C18 cartridges. After derivatization of PQQ with phenyltrimethylammonium hydroxide, molecular peaks at m/z 448 and 462 were used for detection of PQQ and [U-13C]PQQ by selected ion monitoring, respectively. Trace amounts of free PQQ were detected in eight organs, plasma and urine of the human, and in three organs of the rat. The PQQ level was highest in the human spleen (5.9 +/- 3.4 ng/g tissue, followed by the pancreas and lung, and it was below detection limits for human brain and heart. Trace levels of PQQ were also found in rat small intestine, liver and testis. Our data are far below those measured by the redox cycling method of Gallop's group for human plasma, adrenal and urine.

Concerns in the development of an assay for determination of a highly conjugated adsorption-prone compound in human urine.

Concerns in pre-analytical handling of urine samples are discussed using a new KDR kinase inhibitor, 3-[5-(4-methanesulfonyl-piperazin-1-ylmethyl)-1H-indol-2-yl]-1H-quinolin-2-one (compound A), as an example of a case where high light sensitivity and low analyte recovery (high affinity for container surface) were found. The absence of these problems in plasma samples may be a result of the plasma protein content. Low recovery of the analyte from urine can be remedied by either changing the container or by using additives, such as bovine serum albumin (BSA) or non-ionic surfactant Tween-20. In the case of compound A, changing containers (polypropylene versus glass vial) or addition of BSA did bring analyte recovery up to 80%. However, the addition of 0.2% Tween-20 into urine quality controls (QCs) gave more than 95% analyte recovery, indicating effective reduction of analyte loss to the surface of containers. The urine assay using mixed-mode SPE and LC-MS/MS was not affected significantly by introducing Tween-20 into the samples. The mean SPE extraction recovery was 68.4% and matrix suppression of ionization on MS was less than 8% at all analyte concentrations. The linear range of the calibration curve was 0.5-400 ng/mL on PE Sciex API 3000 LC-MS/MS system. The assay intraday accuracy and precision were 92.1-104.8% and <4.2% (%CV), respectively. Urine QC samples, containing 0.2% Tween-20, gave excellent recovery after three cycles of freeze and thaw. Since analyte loss to its urine container surface is not unique to compound A (M. Schwartz, W. Kline, B. Matuszewski, Anal. Chim. Acta 352 (1997) 299-307; A.L. Fisher, E. DePuy, T. Shih, R. Stearns, Y. Lee, K. Gottesdiener, S. Flattery, M. De Smet, B. Keymeulen, D.G. Musson, J. Pharm. Biomed. Anal. 26 (2001) 739-752), we suggest an evaluation of the potential problem in the early stages of urine assay development to ensure reliable quantitation of analytes. The addition of Tween-20 can serve as a useful analytical tool to other analytes with similar situations.

Electrochemical adsorptive behavior of some fluoroquinolones at carbon paste electrode.

Cyclic voltammetry and differential pulse voltammetry were used to explore the adsorption behavior of three antibacterial agents at a carbon paste electrode. The drugs were accumulated on a carbon paste electrode, and a well-defined oxidation peak was obtained in acetate buffer (pH 5.0). The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH and accumulation time. A simple, precise, inexpensive and sensitive voltammetric method has been developed for the determination of the cited drugs (Lomefloxacin (LFX), Sparfloxacin hydrochloride (SFX), and Gatifloxacin (GFX)). A linear calibration was obtained from 2 x 10(-7) M to 4 x 10(-5) M for LFX, 2 x 10(-7) M to 6 x 10(-5) M for SFX, and GFX. The limits of detection (LOD) were 4.2 x 10(-7), 7 x 10(-7) and 6.6 x 10(-7) M, while the limits of quantification (LOQ) were 1.4 x 10(-6), 2.3 x 10(-6) and 2.2 x 10(-6) M for LFX, SFX, and GFX, respectively. The R. S. D. of five measurements at the 1 x 10(-6) M level were 0.4, 0.5 and 0.3 for LFX, SFX and GFX, respectively. The method was applied to the determination of LFX, SFX and GFX in dilute urine samples and dosage forms, and compared with the HPLC method.

Indacaterol determination in human urine: validation of a liquid-liquid extraction and liquid chromatography-tandem mass spectrometry analytical method.

BACKGROUND: Indacaterol is a novel once-a-day inhaled ultra-long-acting ß2-agonist. Quantitative bioanalysis supports pharmacokinetic and clinical research. The aim of the current work was to validate an in-house developed high performance liquid chromatography (HPLC)-tandem mass spectrometry (MS/MS) analytical method for indacaterol determination in human urine samples. METHODS: A liquid-liquid extraction method has been developed to extract indacaterol from human urine samples using ethyl acetate. Indacaterol dry extract was reconstituted with 200 µL of the mobile phase (acidified water:methanol (30:70, v/v)) of which 5 µL was needed for the HPLC-MS/MS analysis. Indacaterol was eluted on a reversed C18 stationary phase with an isocratic mobile phase at a flow of 1 mL/min. Formoterol was the internal standard (IS). The MS/MS detection was employed with a turbo-ion spray ionization in the positive ion mode. A consensus of the international Guidelines for Bioanalytical Method Validation was followed. RESULTS: Indacaterol was detected at a mass to charge ratio (m/z) of 393.3 and its MS/MS daughter at 173.2. The retention times of indacaterol and IS were 1.60 and 1.20 min, respectively. Validated calibration curves were linear over a range of 0.075-100 ng/mL with correlation coefficients (r)≥0.990. The curves' regression weighting factor was 1/x. Method specificity was established in six different human urine batches. No matrix interference was observed. The intra- and inter-batch precision and accuracy within±20% (at lower limit) and±15% (other quality control (QC) levels) were confirmed. The indacaterol mean recovery (precision) percentages at Low, Mid, and High QC levels were 93.5 (3.84), 89.8 (2.15), and 92.2 (2.17), respectively. Short-term, long-term, freeze-thaw, and auto-sampler stability results were accepted. CONCLUSIONS: A specific, accurate and precise HPLC-MS/MS method has been validated for indacaterol quantification in human urine. This simple method is reproducible and robust to support future, indacaterol-related pharmacokinetic, bioequivalence and clinical studies.

The redox-cycling assay is not suited for the detection of pyrroloquinoline quinone in biological samples.

Based on the results of the so-called redox-cycling assay it has been claimed that various common foods and beverages as well as mammalian body fluids and tissues contain substantial quantities (microM) of free PQQ [M. Paz et al. (1989) in: PQQ and Quinoproteins (J.A. Jongejan and J.A. Duine, eds.) Kluwer Academic Publishers, Dordrecht, pp. 131-143 and J. Killgore et al. (1989) Science 245, 850-852]. However, by investigating samples from such sources with a biological assay of nM sensitivity, we could not confirm these claims. Analysis of the samples with procedures that proved adequate for the detection of PQQ adducts and conjugates gave equally negative results. To account for the positive response in the redox-cycling assay, as opposed to the negative results obtained by other methods, a search was made for those substances in these samples that caused the false-positive reactions. It was found that a number of commonly occurring biochemicals like ascorbic and dehydroascorbic acid, riboflavin and to a lesser extent pyridoxal phosphate, gave a positive response in the redox-cycling assay. The amounts of these interfering substances that were determined in the samples by independent methods could well explain the response. In separate experiments it was found that the effect of PQQ added to biological samples was obscured over an appreciable range of concentrations. For these reasons it must be concluded that the redox-cycling assay is not suited for the detection of PQQ in these samples. Any claims that are based on the results of this method should be disregarded.