A rapid and efficient analytical method for the quantification of a novel anticholinergic compound, R-phencynonate, by stable isotope-dilution LC-MS/MS and its application to bioavailability and dose proportionality studies.

A rapid, specific and high-throughput stable isotope-dilution LC-MS/MS method was developed and validated with high sensitivity for the quantification of R-phencynonate (a eutomer of phencynonate racemate) in rat and dog plasma. Plasma samples were deproteinized using acetonitrile and then separated on a C8 column with an isocratic mobile phase containing acetonitrile-water-formic acid mixture (60:40:0.1, v/v/v) at a flow rate of 0.2 mL/min. Each sample had a total run time of 3 min. Quantification was performed using triple quadrupole mass spectrometry in selected reaction monitoring mode with positive electrospray ionization. The method was shown to be highly linear (r2 > 0.99) and to have a wide dynamic range (0.1-100 ng/mL) with favourable accuracy and precision. No matrix effects were observed. The detailed pharmacokinetic profiles of R-phencynonate at therapeutic doses in rats and dogs were characterized by rapid oral absorption, quick clearance, high volume of distribution and poor absolute bioavailability. R-Phencynonate lacked dose proportionality over the oral dose range, based on the power model. However, the area under concentration-time curve and the maximum plasma concentration increased linearly in a dose-dependent manner in both animal models. The absolute bioavailability of R-phencynonate was 16.6 ± 2.75 and 4.78 ± 1.26% in dogs and rats, respectively.

Simultaneous determination of levophencynonate and its metabolite demethyl levophencynonate in human plasma by liquid chromatography tandem mass spectrometry.

A sensitive and convenient high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method was developed to determine levophencynonate and demethyl levophencynonate levels in human plasma simultaneously. Chromatographic separation was achieved on a SHIMADZU Shim-Pack XR C8 column and mass spectrometric analysis was performed by an API5000 mass spectrometer coupled with an electro-spray ionization (ESI) source in the positive ion mode. The MRM transitions of m/z 358.4→156.4 and 344.5→144.2 were used to quantify levophencynonate and demethyl levophencynonate, respectively. This analytical method was fully validated with specificity, linearity, lower limit of quantitation (LLOQ), accuracy, precision, stability, matrix effect and recovery. The linearity of this method were developed to be within the concentration ranges of 10-4000pg/mL for levophencynonate and 25-8000pg/mL for demethyl levophencynonate in human plasma. This method was used in a clinical study which was administrated with single oral dose for Chinese healthy subjects to investigate the pharmacokinetics of levophencynonate and demethyl levophencynonate.

Simultaneous quantification of phencynonate and its active metabolite N-demethyl phencynonate in human plasma using liquid chromatography and isotope-dilution mass spectrometry.

A sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to simultaneously quantify phencynonate (PCN) and its major metabolite N-demethyl phencynonate (DM-PCN) in human plasma. Following one-step liquid-liquid extraction, the analytes were separated on a reversed-phase C18 column. Methanol and 0.02% formic acid in 10 mM ammonium acetate (62:38, v/v) was used as isocratic mobile phase at a flow-rate of 0.3 mL/min. An API 5000 tandem mass spectrometer equipped with a Turbo IonSpray ionization source was used as the detector and was operated in the positive ion mode. Multiple reaction monitoring using the transition of m/z 358.4 → m/z 156.2, m/z 344.4 → m/z 142.2, and m/z 361.3 → m/z 159.2 was performed to quantify PCN, DM-PCN, and the internal standard (D3 -PCN), respectively. This approach showed a lower limit of quantification of 10 pg/mL and 25 pg/mL for PCN and DM-PCN in plasma, respectively. This sensitivity was at least 50-fold superior to previously reported ones and thus enabled the approach well applicable to low-dose pharmacokinetic studies. The intra- and inter-day precisions were less than 14.2 % at each QC level for both PCN and DM-PCN. The inter-day relative errors ranged from -1.9% to -4.9% for PCN, and from 0.6% to 6.4% for DM-PCN. As a proof of principle, the validated method was successfully applied to simultaneous quantification of circulating PCN and DM-PCN in healthy subjects after a single oral administration of 2 mg phencynonate hydrochloride pellet.

Trend analysis of plasma insulin level around parturition in relation to parity in Saanen goats.

The present study investigated the effect of parity on plasma insulin level around parturition in Saanen goats. On d -14, -7, 0, 3, 7, 10, and 14 from parturition, plasma glucose, NEFA, free AA, cortisol, and insulin concentrations were analyzed in 10 primiparous and 10 multiparous goats. At parturition, BW of primiparous goats was about 75% of that of multiparous ones (P < 0.001) and then their milk production was lower than that of multiparous ones (P < 0.001). At parturition, glucose increased (P < 0.01) in both primiparous and multiparous goats and then decreased (P < 0.01) on d 3 of lactation, remaining higher (P < 0.01) in primiparous than multiparous goats until the end of the study period. In both groups, free AA decreased (P < 0.01) at parturition, returning to prepartum levels (P < 0.01) on d 3 of lactation without difference between groups. Only in multiparous goats, plasma NEFA increased at parturition (P < 0.01), returning to prepartum levels on d 14 (P < 0.01). Changes in glucose and AA could have been caused by cortisol, which increased (P < 0.01) at parturition in both primiparous and multiparous goats, returning to prepartum levels (P < 0.01) on d 7 of lactation, without difference between the parity groups. In multiparous goats, insulin decreased soon after parturition (P < 0.05), remaining at low levels until the end of the study period, whereas in primiparous goats, insulin did not vary until d 14 of lactation, when it decreased (P < 0.05) also in this group. Therefore, between d 3 and 14 of lactation, insulin was higher in primiparous than multiparous goats (P < 0.05). Only in primiparous goats, at kidding, insulin was negatively correlated to BW (P < 0.01), and after parturition it was negatively correlated with milk yield (P < 0.05) and plasma NEFA (P < 0.05). We hypothesize that higher insulin levels in primiparous Saanen goats, which are still immature at their first breeding season, acted to limit both the mobilization of bodily reserves and the capture of nutrients by the lactating mammary gland, thus providing nutrients for their own physical and physiological development.

Effects of probucol, a typical hERG expression inhibitor, on in vivo QT interval prolongation in conscious dogs.

The cholesterol-lowering drug, probucol, is known to induce QT interval prolongation and torsades de pointes in patients. Recent in vitro studies have indicated that probucol reduces hERG expression in the plasma membrane and does not directly block human ether-a-go-go-related gene (hERG) channels. The present study was performed to investigate the effects of probucol on in vivo QT interval prolongation. Epicardial electrocardiograms were recorded in conscious dogs given oral single or repeated (7 days) doses of probucol (100mg/kg), and in combination with moxifloxacin (20mg/kg). QTc intervals were analyzed by a probabilistic method with individual rate collection formulae. Values of change in QTc (QTc) interval and its integration from 1 to 21 h (AUC1-21h) were calculated to evaluate drug-induced QT prolongation. A single dose of probucol slightly but significantly increased the AUC1-21h QTc interval on days 2 and 3. The QT prolongation was markedly augmented by repeated doses of probucol in a time-dependent manner, despite the lack of increase in plasma concentration. The combination of probucol and moxifloxacin produced additive effects on QT interval prolongation. These results suggest that long-term exposure to the hERG expression inhibitor, probucol, is required to evaluate its maximal effects on in vivo QT interval prolongation. A combination of direct and indirect hERG inhibitors may produce simple additive effects on QT interval prolongation.

Simultaneous quantification of linezolid, tinidazole, norfloxacin, moxifloxacin, levofloxacin, and gatifloxacin in human plasma for therapeutic drug monitoring and pharmacokinetic studies in human volunteers.

BACKGROUND: Linezolid may be administered in combination with norfloxacin, gatifloxacin, levofloxacin, moxifloxacin, and tinidazole for the treatment of various infections, such as urinary and respiratory tract infections, to improve the efficacy of the treatment or to reduce the duration of therapy. Knowledge of the antibiotic plasma concentrations combined with bacterial susceptibility evaluated in terms of minimum inhibitory concentration would optimize treatment efficacy while limiting the risk of dose-related adverse effects and avoiding suboptimal concentrations. METHODS: A new high-performance liquid chromatography assay method was developed and validated for determination of the above-mentioned drugs in small samples of human plasma. After protein precipitation with acetonitrile:methanol (1:1, vol/vol), satisfactory separation was achieved on a Hypersil BDS C18 column (250 × 4.6 mm, 5 µm) using a mobile phase comprising 20 mM sodium dihydrogen phosphate-2 hydrate (pH = 3.2) and acetonitrile at a ratio of 75:25, vol/vol; the elution was isocratic at ambient temperature with a flow rate of 1.5 mL/min. The ultraviolet detector was set at 260 nm. The validated method was applied to assay real plasma samples used for pharmacokinetic studies and therapeutic drug monitoring of the selected drugs. RESULTS: The assay method described was found to be rapid, sensitive, reproducible, precise, and accurate. Linearity was demonstrated over the concentration ranges as follows: 0.1-30 µg/mL for linezolid and tinidazole; 0.05-5 µg/mL for norfloxacin; and 0.1-10 µg/mL for moxifloxacin, levofloxacin, and gatifloxacin (mean r = 0.9999, n = 12). The observed within- and between-day assay precisions were within 12.5%, whereas accuracy ranged between 92.0% and 112% for all the analytes. The lower limit of quantification was 0.1 µg/mL for all the analytes except norfloxacin which was 0.05 µg/mL. CONCLUSIONS: This assay method was valid within a wide range of plasma concentrations and may be proposed as a suitable method for pharmacokinetic studies, therapeutic drug monitoring implementation, and routine clinical applications, especially for some populations of patients who receive a combination of these drugs.

Comparative evaluation of aqueous and plasma concentration of topical moxifloxacin alone and with flurbiprofen in patients of cataract surgery.

OBJECTIVES: To determine the aqueous and plasma concentrations of moxifloxacin administered topically alone and with flurbiprofen in patients undergoing cataract surgery. MATERIALS AND METHODS: A total of 50 subjects scheduled for routine cataract surgery were randomly allocated to two groups (n = 25 each). Group-1 patients were treated with topical moxifloxacin alone: One drop 6 times/day for 3 days before surgery and one drop 4 times on the day of surgery: Group-2 patients were treated with topical moxifloxacin as in Group-1 and with topical flurbiprofen: One drop 4 times/day for 3 days before and on the day of surgery. The interval between two drugs was 30 min for last 3 days and 15 min on the day of surgery. Last dose was administered 1 h before aqueous humor and blood sampling for both the groups. The antibiotic concentration in aqueous humor and plasma were determined by using high performance liquid chromatography. RESULTS: The mean concentration of moxifloxacin in aqueous humor was 1.71 ± 0.82 mg/ml in Group-1 and 2.39 ± 1.34 mg/ml in Group-2. Concentrations of moxifloxacin in aqueous humor were significantly higher in Group-2 than that of Group-1. CONCLUSION: Flurbiprofen may increase the concentration of moxifloxacin in aqueous humor.

Biopharmaceutical characterization, metabolism, and brain penetration of the triple reuptake inhibitor amitifadine.

Amitifadine (EB-1010, formerly DOV 21,947) is a serotonin-preferring triple reuptake inhibitor that is a drug candidate for major depressive disorder. We investigated several relevant biopharmaceutic and drug-like characteristics of amitifadine using in vitro methodology and additionally determined the in vivo brain to plasma ratio of the drug in rats. Amitifadine was highly plasma protein bound with over 99% of drug bound to human plasma proteins. Using Caco-2 cell lines, amitifadine was bidirectionally highly permeable and showed no evidence of active secretion. Amitifadine was metabolized slowly by human hepatocytes and the major metabolite was the lactam EB-10101. In vitro studies using human liver microsomes demonstrated that EB-10101 was formed by monoamine oxidase A (MAO-A) and a NADPHdependent enzyme, possibly a cytochrome P450 (CYP) isoform. Amitifadine was a moderate inhibitor of the human isoforms of the major drug metabolizing enzymes CYP2D6, CYP3A4, CYP2C9, and CYP2C19 (IC50 = 9 - 100 µM), but was a potent inhibitor of human CYP2B6 (IC50 = 1.8 µM). The brain to plasma ratio for amitifadine varied from 3.7 - 6.5 at various time points, indicating preferential partitioning into rat brain versus plasma. The low affinity for the major drug metabolizing CYP enzymes and metabolism by multiple pathways may reduce pharmacokinetic drug-drug interactions and effects of enzyme polymorphisms. Overall, these studies suggest that amitifadine has drug-like characteristics favorable for drug development.

Pharmacokinetics of moxifloxacin and high-dose levofloxacin in severe lower respiratory tract infections.

This study evaluated the pharmacokinetics of intravenous moxifloxacin 400 mg once and levofloxacin 500 mg twice daily in patients with lower respiratory tract infections (LRTIs) and assessed their pharmacodynamic adequacy against common respiratory pathogens. Eighteen patients with LRTIs hospitalised in general wards were included. Serial blood samples were obtained at steady state and concentrations were determined using HPLC. Pharmacokinetic variables were estimated by a two-compartment model. The characteristic pharmacodynamic parameter for fluoroquinolones (AUC(0-24)/MIC) was calculated. Peak and trough concentrations were, respectively, 4.81 ± 1.03 and 0.59 ± 1.13 mg/L for moxifloxacin and 6.42 ± 1.08 and 0.79 ± 0.39 mg/L for levofloxacin. Pharmacokinetic data for moxifloxacin and levofloxacin, respectively, were: CL, 10.27 ± 1.24 and 22.66 ± 6.62 L/h; t1/2, 13.43 ± 5.12 and 6.75 ± 1.34 h; Vss, 163.03 ± 53.88 and 170.73 ± 39.59 L; and AUC(0-24), 39.38 ±5.28 and 47.06 ± 14.09 mg·h/L. The pharmacodynamic target was attained in all patients by both antibiotics against the majority of respiratory pathogens. Moxifloxacin proved to be pharmacodynamically efficacious against Gram-positive bacteria with MICs ≤ 0.79 mg/L and Gram-negative bacteria with MICs ≤ 0.32 mg/L. These MIC thresholds for levofloxacin were 1.1 mg/L and 0.38 mg/L, respectively. Moxifloxacin and high-dose levofloxacin show a favourable pharmacokinetic profile in plasma of patients with severe LRTIs, without significant interpatient variability. They ensure optimal pharmacodynamic exposure against the majority of microbes involved in these infections. However, the predicted efficacy against Gram-negative bacteria with MICs ≥ 0.5 mg/L appears to be low.

Pharmacokinetics of moxifloxacin in critically ill patients with impaired renal function undergoing pulse high-volume haemofiltration.

Moxifloxacin is an 8-methoxy quinolone with a broad spectrum of activity against clinically important pathogens. The aim of this study was to investigate the pharmacokinetics of intravenous (i.v.) moxifloxacin in critically ill patients with impaired renal function undergoing pulse high-volume haemofiltration (PHVHF) (n=8) to provide a reference for clinical rational moxifloxacin use in these patients. Blood and ultrafiltrate samples were obtained following i.v. infusion of a single 400 mg moxifloxacin dose. Concentrations of moxifloxacin in serum and ultrafiltrate were determined by HPLC analysis with fluorometric detection. Pharmacokinetics of moxifloxacin in plasma and ultrafiltrate were best described by a two-compartment model. Peak and trough serum moxifloxacin concentrations were 4.84 ± 1.85 mg/L and 1.17 ± 0.73 mg/L, respectively, at the arterial port after a single i.v. 400 mg dose. The mean elimination half-life was 4.82 ± 2.13 h, the volume of distribution was 82.63 ± 24.69 L and the calculated AUC(0-12) was 26.91 ± 10.96 mgh/L. Total clearance was 14.36 ± 8.44 L/h and the clearance of haemofiltration was 1.67 ± 0.95 L/h.C(max)/MIC(90) ratios and predicted AUC(0-24)/MIC(90) ratios were above the cut-off points for common pathogens that indicate clinical success. A single 400 mg i.v. dose of moxifloxacin is safe and efficacious in the treatment of critically ill patients infected with clinically common pathogens and impaired renal function undergoing PHVHF. It also should be kept in mind that the standard dose is not sufficient for this population infected with pathogens with a higher MIC(90) (0.5 mg/L).

The effect of the molecular adsorbent recirculating system on moxifloxacin and meropenem plasma levels.

BACKGROUND: Adequate plasma antibiotic concentrations are necessary for effective elimination of invading microorganism; however, extracorporeal organ support systems are well known to alter plasma concentrations of antibiotics, requiring dose adjustments to achieve effective minimal inhibitory concentrations in the patient's blood. METHODS: A mock molecular adsorbent recirculating system (MARS) circuit was set using 5000 ml of bovine heparinized whole blood to simulate an 8-h MARS treatment session. After the loading dose of 400 mg of moxifloxacin or 2 g of meropenem had been added, blood was drawn from the different parts of the MARS circuit at various time points and analyzed by high-performance liquid chromatography. The experiments were performed in triplicate. Additionally, meropenem concentrations were determined in the plasma of one patient treated with MARS suffering from acute liver failure due to an idiosyncratic reaction to immunosuppressive medication. RESULTS: In our single-compartment model, a significant decrease in the quasi-systemic concentration of moxifloxacin and meropenem could be detected as early as 15 min after the commencing of the MARS circuit. Moreover, within 60 min the moxifloxacin and meropenem concentrations were less than 50% of the initial value. The activated charcoal removed the majority of moxifloxacin and meropenem in the albumin circuit. In our patient, the meropenem concentrations in the return line after MARS were constantly lower than in the access line, indicating a likely removal of meropenem through MARS. CONCLUSION: Our data provide evidence that moxifloxacin and meropenem are effectively removed from the patient's blood by MARS, leading to low plasma levels. Dose adjustments of both antibiotic compounds may be required.

In vivo metabolic investigation of moxifloxacin using liquid chromatography/electrospray ionization tandem mass spectrometry in combination with online hydrogen/deuterium exchange experiments.

RATIONALE: Tuberculosis is a leading cause of death from an infectious disease and moxifloxacin is an effective drug as compared to other fluoroquinolones. To date only two metabolites of the drug are known. Therefore, the present study on characterization of hitherto unknown in vivo metabolites of moxifloxacin using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is undertaken. METHODS: In vivo metabolites of moxifloxacin have been identified and characterized by using LC/ESI-MS/MS in combination with an online hydrogen/deuterium (H/D) exchange technique. To identify in vivo metabolites, blood, urine and faeces samples were collected after oral administration of moxifloxacin to Sprague-Dawley rats. The samples were prepared using an optimized sample preparation approach involving protein precipitation, liquid-liquid extraction followed by solid-phase extraction and LC/MS/MS analysis. RESULTS: A total of nine phase I and ten phase II metabolites of moxifloxacin have been identified in urine samples including N-sulphated, glucuronide and hydroxylated metabolites which are also observed in plasma samples. In faeces samples, only the N-sulphated metabolite is observed. The structures of metabolites have been elucidated based on fragmentation patterns, accurate mass measurements and online H/D exchange LC/MS/MS experiments. Online H/D exchange experiments are used to support the identification and structural characterization of drug metabolites. CONCLUSIONS: A total of 19 in vivo metabolites of moxifloxacin have been characterized using LC/ESI-MS/MS in combination with accurate mass measurements and online H/D exchange experiments. The main phase I metabolites of moxifloxacin are hydroxylated, decarbonylated, desmethylated and desmethylhydroxylated metabolites which undergo subsequent phase II glucuronidation pathways.

Moxifloxacin population pharmacokinetics in patients with pulmonary tuberculosis and the effect of intermittent high-dose rifapentine.

We described the population pharmacokinetics of moxifloxacin and the effect of high-dose intermittent rifapentine in patients with pulmonary tuberculosis who were randomized to a continuation-phase regimen of 400 mg moxifloxacin and 900 mg rifapentine twice weekly or 400 mg moxifloxacin and 1,200 mg rifapentine once weekly. A two-compartment model with transit absorption best described moxifloxacin pharmacokinetics. Although rifapentine increased the clearance of moxifloxacin by 8% during antituberculosis treatment compared to that after treatment completion without rifapentine, it did not result in a clinically significant change in moxifloxacin exposure.

Penetration of moxifloxacin into liver tissue.

Moxifloxacin is considered for treatment of pyogenic liver abscesses as well as antibiotic prophylaxis in the case of hepatobiliary interventions. The aim of this study was to provide data on the pharmacokinetic (PK) profile of moxifloxacin in serum and liver tissue of patients undergoing liver resection due to primary or secondary tumours of the liver. Patients scheduled for liver resection (n=34) received moxifloxacin 400 mg at randomised time intervals prior to surgery. Blood and healthy liver tissue were sampled 1.5-26 h after administration of moxifloxacin. Immediately after centrifugation, plasma was separated, frozen and stored until analysis. In a subgroup of 19 patients, additional plasma specimens were obtained after 2, 4, 8, 12, 24, 36 and 48 h to assess the PK profile. PK parameters of moxifloxacin were calculated applying a two-compartment model. Median (interquartile range) PK parameters were as follows: peak concentration at the end of moxifloxacin infusion (C(max)), 6.0 mg/L (4.8-7.1 mg/L); area under the concentration-time curve extrapolated to infinity (AUC(0-∞)), 51.1 mgh/L (40.3-57.7 mgh/L); elimination half-life, 13.2h (11.0-14.1 h); volume of distribution at steady state (V(ss)), 138.7 L (102.7-168.5 L); and total body clearance (CL), 7.8 L/h (6.9-9.9L/h). Mean tissue concentrations were 9.13 mg/kg after 1.6-2.4 h, 7.62 mg/kg after 2.6-4.9h, 7.48 mg/kg after 5.6-10.0 h and 6.24 mg/kg after 22.9-26.5 h. Mean tissue:serum ratios were 2.9, 3.4, 5.0 and 12.3, respectively. The lowest tissue concentration found in the study at any time point was 2.8 mg/kg. In conclusion, moxifloxacin rapidly penetrates into the liver tissue where its concentration remains high following intravenous administration. Therefore, intravenously applied moxifloxacin might be used for the treatment of bacterial liver infections such as pyogenic liver abscess as well as in pre-operative prophylaxis.

No effect of a single supratherapeutic dose of lersivirine, a next-generation nonnucleoside reverse transcriptase inhibitor, on corrected QT interval in healthy subjects.

The objective of this study was to investigate the effect of a supratherapeutic dose of lersivirine (LRV) on corrected QT (QTc) interval using Fridericia's equation (QTcF) in healthy subjects. In this randomized, single-dose, placebo- and active-controlled 3-way crossover study, healthy adult males (n = 48) were randomized to receive LRV (2,400 mg), moxifloxacin (400 mg), or placebo for each treatment period. Triplicate 12-lead electrocardiogram measurements were performed, PK samples were collected, and vital signs were measured. Adverse event monitoring and safety laboratory testing were performed. All subjects were white (mean age, 39 years; body mass index [BMI], 25.6 kg/m(2)) and completed the study. Following LRV administration, the upper bound of the 90% confidence interval (CI) for time-matched adjusted mean differences to placebo QTcF at each time point postdose was below the regulatory threshold of 10 ms, satisfying the criteria for a negative thorough QT/QTc study. The highest upper bound of QTcF 90% CI occurred at 6 h for LRV (3.32 ms; 90% CI, 1.47 to 5.17 ms). The study was deemed adequately sensitive as the lower bound of the 90% CI for the adjusted mean QTcF differences between moxifloxacin and placebo at the moxifloxacin historical T(max) of 3 h was >5 ms (15.29 ms; 90% CI, 13.44 to 17.14 ms). There was no statistically significant relationship between LRV exposure and placebo-adjusted change from baseline QTcF or clinically significant changes in QRS complex, pulse rate (PR) interval, heart rate, or blood pressure. LRV (2,400 mg) did not prolong the QTcF interval, and no clinically relevant electrocardiogram or vital sign changes were observed in healthy subjects.

Development and validation of liquid chromatography-mass spectrometric method for simultaneous determination of moxifloxacin and ketorolac in rat plasma: application to pharmacokinetic study.

A highly sensitive, selective and rapid liquid chromatography-electrospray ionization mass spectrometry (LC-MS) method has been developed and validated for simultaneous determination of moxifloxacin (MFX) and ketorolac (KTC) in rat plasma. Gemifloxacin (GFX) was used as an internal standard (IS). A simple protein precipitation method was used for the extraction of analytes from rat plasma. Effective chromatographic separation of MFX, KTC and GFX was achieved on a Kromasil C(18) column (100 × 4.6 mm, 5 µm) using a mobile phase consisting of acetonitrile-10 mm ammonium acetate (pH 2.5)-0.1% formic acid (50:25:25) in an isocratic elution, followed by detection with positive ion electrospray ionization mass spectrometry using target ions of [M + H](+) at m/z 402 for MFX, m/z 256 for KTC and m/z 390 for GFX in selective ion recording mode. The method was validated over the calibration range of 5-100 ng/mL for MFX and 10-6000 ng/mL for KTC. The method demonstrated good performances in terms of intra- and inter-day precision (0.97-5.33%) and accuracy (93.91-101.58%) for both MFX and KTC, including lower and upper limits of quantification. The recoveries from spiked control samples were >75% for MFX and >79% for KTC. The matrix effect was found to be negligible and the stability data were within acceptable limits. Further, the method was also successfully applied to a single-dose pharmacokinetic study in rats. This method can be extended to measure plasma concentrations of both drugs in human to understand drug interaction and adverse effects.

Spectrofluorimetric study of the interaction between europium(III) and moxifloxacin in micellar solution and its analytical application.

A sensitive spectrofluorimetric method has been developed for the determination of moxifloxacin (MOX) using europium(III)-MOX complex as a fluorescence probe in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS). The fluorescence (FL) intensity of Eu(3+) was enhanced by complexation with MOX at 614 nm after excitation at 373 nm. The FL intensity of the Eu(3+)-MOX complex was significantly intensified in the presence of SDBS. Under the optimum conditions, it was found that the enhanced FL intensity of the system showed a good linear relationship with the concentration of MOX over the range of 1.8 × 10(-11)-7.3 × 10(-9) g mL(-1) with a correlation coefficient of 0.9998. The limit of detection of MOX was found to be 2.8 × 10(-12) g mL(-1) with relative standard deviation (RSD) of 1.25% for 5 replicate determination of 1.5 × 10(-8) g mL(-1) MOX. The proposed method is simple, offers higher sensitivity with wide linear range and can be successfully applied to determine MOX in pharmaceutical and biological samples with good reproducibility. The luminescence mechanism is also discussed in detail with ultraviolet absorption spectra.

Reevaluation of moxifloxacin pharmacokinetics and their direct effect on the QT interval.

The objectives of this study were to investigate the population pharmacokinetics of moxifloxacin and their relationship with the observed QT interval as well as the effect of covariates in healthy subjects using nonlinear mixed-effects modeling. A pool of 4 thorough QT studies were used, representing 99 healthy subjects who received moxifloxacin. The data were modeled using Monolix. Moxifloxacin pharmacokinetics were ascribed a 2- compartment open model. The TRANSIT model provided a better description of the delay in absorption than did the LAG model. The most significant covariate was lean body mass (LBM). The population estimates for clearance and central volume of distribution were 10.0 L/h per 60 kg of LBM and 131 L per 60 kg of LBM, respectively. The effect of moxifloxacin on QT was investigated using a direct effect model. The SLOPE model, relating the QT increase as a linear function of concentration, provided a better description of the pharmacodynamic effect than did the Emax model. The unique covariate was gender for both baseline QT and individual heart rate correction factor. The pharmacokinetics of moxifloxacin were satisfactorily described by an open 2-compartmental model with linear elimination. The trigonometric equation with a direct and proportional concentration effect satisfactorily described the effect on QT.

Effect of rifampicin & isoniazid on the steady state pharmacokinetics of moxifloxacin.

BACKGROUND & OBJECTIVES: Moxifloxacin (MFX) is reported to have promising antimycobacterial activity, and has a potential to shorten tuberculosis (TB) treatment. We undertook this study to examine the influence of rifampicin (RMP) and isoniazid (INH) on the steady state pharmacokinetics of MFX individually in healthy individuals. METHODS: A baseline pharmacokinetic study of MFX (400 mg once daily) was conducted in 36 healthy adults and repeated after one week of daily MFX with either RMP (450/600 mg) (n = 18) or INH (300 mg) (n = 18). Plasma MFX concentrations were determined by a validated HPLC method. RESULTS: Plasma peak concentration and exposure of MFX was significantly lower and plasma clearance significantly higher when combined with RMP (P<0.001). The C max to MIC and AUC 0-12 to MIC ratios of MFX were significantly lower during concomitant RMP (P<0.001). INH had no significant effect on the pharmacokinetics of MFX. INTERPRETATION & CONCLUSIONS: Concomitant RMP administration caused a significant decrease in C max and AUC 0-12 of MFX, the mean decreases being 26 and 29 per cent, respectively. It is uncertain whether this decrease would affect the treatment efficacy of MFX. Prospective studies in TB patients are needed to correlate MFX pharmacokinetics with treatment outcomes.

Pharmacokinetic evaluation of the penetration of antituberculosis agents in rabbit pulmonary lesions.

Standard antituberculosis (anti-TB) therapy requires the use of multiple drugs for a minimum of 6 months, with variable outcomes that are influenced by a number of microbiological, pathological, and clinical factors. This is despite the availability of antibiotics that have good activity against Mycobacterium tuberculosis in vitro and favorable pharmacokinetic profiles in plasma. However, little is known about the distribution of widely used antituberculous agents in the pulmonary lesions where the pathogen resides. The rabbit model of TB infection was used to explore the hypothesis that standard drugs have various abilities to penetrate lung tissue and lesions and that adequate drug levels are not consistently reached at the site of infection. Using noncompartmental and population pharmacokinetic approaches, we modeled the rate and extent of distribution of isoniazid, rifampin, pyrazinamide, and moxifloxacin in rabbit lung and lesions. Moxifloxacin reproducibly showed favorable partitioning into lung and granulomas, while the exposure of isoniazid, rifampin, and pyrazinamide in lesions was markedly lower than in plasma. The extent of penetration in lung and lesions followed different trends for each drug. All four agents distributed rapidly from plasma to tissue with equilibration half-lives of less than 1 min to an hour. The models adequately described the plasma concentrations and reasonably captured actual lesion concentrations. Though further refinement is needed to accurately predict the behavior of these drugs in human subjects, our results enable the integration of lesion-specific pharmacokinetic-pharmacodynamic (PK-PD) indices in clinical trial simulations and in in vitro PK-PD studies with M. tuberculosis.