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.

Limited-sampling strategies for therapeutic drug monitoring of moxifloxacin in patients with tuberculosis.

BACKGROUND: Moxifloxacin (MFX) is a potent drug for multidrug resistant tuberculosis(TB) treatment and is also useful if first-line agents are not tolerated. Therapeutic drug monitoring may help to prevent treatment failure. Obtaining a full concentration-time curve of MFX for therapeutic drug monitoring is not feasible in most settings. Developing a limited-sampling strategy based on population pharmacokinetics (PK) may help to overcome this problem. METHODS: Steady-state plasma concentrations after the administration of 400 mg of MFX once daily were determined in 21 patients with TB, using a validated liquid chromatography-tandem mass spectrometry method. A one-compartment population model was generated and crossvalidated. Monte Carlo data simulation (n=1000) was used to calculate limited-sampling strategies. The correlation between predicted MFX AUC0-24h (area under the concentration-time curve 0 to 24 hours) and observed AUC0-24h was investigated by Bland-Altman analysis. Finally, the predictive performance of the final model was tested prospectively using MFX profiles from patients with TB receiving 400, 600, or 800 mg once daily. RESULTS: Median minimum inhibitory concentration of Mycobacterium tuberculosis isolates was 0.25 mg/L (interquartile range: 0.25-0.5 mg/L). The geometric mean AUC0-24h was 24.5 mg·h/L (range: 8.5-72.2 mg·h/L), which resulted in a geometric mean AUC0-24h/minimum inhibitory concentration ratio of 72 (range: 21-321). PK analysis, based on PK profiles of 400 mg of MFX once daily, resulted in a crossvalidated population PK model with the following parameters: apparent clearance (Cl) 18.5±8.6 L/h per 1.85 m, Vd 3.0±0.7 L/kg corrected lean body mass, Ka 1.15±1.16 h, and F was fixed at 1. After the Monte Carlo simulation, the best predicting strategy for MFX AUC0-24h for practical use was based on MFX concentrations 4 and 14 hours postdosing (r=0.90, prediction bias=-1.5%, and root mean square error=15%). CONCLUSIONS: MFX AUC0-24h in patients with TB can be predicted with acceptable accuracy for clinical management, using limited sampling. AUC0-24h prediction based on 2 samples, 4 and 14 hours postdose, can be used to individualize treatment.

Cardiovascular safety assessments in the conscious telemetered dog: utilisation of super-intervals to enhance statistical power.

INTRODUCTION: ICH S7A and S7B guidelines recommend the use of conscious animals for assessment of non-clinical cardiovascular safety of new chemical entities prior to testing in humans. Protocol design and data analysis techniques can affect the quality of the data produced and can therefore ultimately influence the clinical management of cardiovascular risk. It is therefore essential to have an understanding of the magnitude of changes detectable and the clinical relevance of these changes. This paper describes the utilisation of "super-intervals" to analyse and interpret data obtained from our conscious telemetered dog cardiovascular safety protocol and reports the statistical power achieved to detect changes in various cardiovascular parameters. METHODS: Cardiovascular data from 18 dog telemetry studies were used to calculate the statistical power to detect changes in cardiovascular parameters. Each study followed a test compound versus vehicle cross-over experimental design with 24h monitoring (n=4). 1 min mean raw data from each individual animal was compressed into 15 min mean data for each dose group for visualisation. Larger summary periods, or "super-intervals", were then selected to best represent any observed cardiovascular effects whilst taking into account the pharmacokinetic profile of the drug e.g. intervals of 1 to 6, 7 to 14 and 14 to 22h post-dose. RESULTS: With this methodology and study design we predict, using the median percentile that our studies have 80% power to detect the following changes: HR (+/-10bpm), LV +dP/dt max (+/-375mmHg/s), MBP (+/-5mmHg) and QTc (+/-4ms). DISCUSSION: Super-intervals are a simple way to handle the high degree of natural variability seen with any ambulatory cardiovascular assessment and, in our hands, result in highly statistically powered studies. The ability of this model to detect cardiovascular changes of small, but biologically relevant, magnitude enables confident decision making around the cardiovascular safety of new chemical entities.

Serum and prostatic tissue concentrations of moxifloxacin in patients undergoing transurethral resection of the prostate.

The spectrum of pathogens causing chronic bacterial prostatitis comprises Gram-negative, Gram-positive and atypical microorganisms. Because of its broad spectrum of activity, the group 4 fluoroquinolone moxifloxacin might be a suitable antibiotic for treatment of bacterial prostatitis. The aim of this prospective study was to investigate the penetration of moxifloxacin into prostatic tissue in patients with benign prostatic hyperplasia. Patients received a single dose of moxifloxacin 400 mg in an 1 hour lasting infusion (250 ml) for perioperative prophylaxis before undergoing transurethral resection of the prostate (TURP). Serum concentrations were determined in all patients before infusion, at the end of infusion (time point 0), 0.5, 1 and 2 h after the end of infusion. Patients were randomized for tissue sampling either 0, 0.5, 1 or 2 h after the end of infusion. At beginning of TURP approximately 1 g of tissue was sampled for analysis. Concentrations of moxifloxacin in serum and tissue were determined by HPLC. 39 patients were evaluated. Median serum and prostatic tissue concentrations peaked at 0 h (4.94 mg/ L and 8.50 mg/ kg, respectively). The lowest concentrations were quantified at 2 h after the end of infusion (2.46 mg/ L and 3.88 mg/ kg, respectively). The prostatic tissue concentrations of moxifloxacin were approximately twice as high as in corresponding serum. At the end of infusion the tissue and serum concentrations seemed to be already equilibrated, as their ratios did not differ significantly during the time of investigation. After an intravenous infusion of 400 mg the serum and prostatic tissue concentrations of moxifloxacin were well above the MIC values of most important prostatic pathogens. The high tissue/ serum ratio and the extended antibacterial spectrum suggests active concentration in the prostate which may translate into increased efficacy compared to group 2 and 3 fluoroquinolones in the treatment of chronic bacterial prostatitis.

QT prolongation and proarrhythmia by moxifloxacin: concordance of preclinical models in relation to clinical outcome.

Moxifloxacin, a fluoroquinolone antibiotic associated with QT prolongation, has been recommended as a positive control by regulatory authorities to evaluate the sensitivity of both clinical and preclinical studies to detect small but significant increases in QT interval measurements. In this study, we investigated effects of moxifloxacin on the hERG current in HEK-293 cells, electrocardiograms in conscious telemetered dogs, and repolarization parameters and arrhythmogenic potentials in the arterially perfused rabbit ventricular wedge model. Moxifloxacin inhibited the hERG current with an IC50 of 35.7 microM. In conscious telemetered dogs, moxifloxacin significantly prolonged QTc at 30 and 90 mg kg(-1), with mean serum Cmax of 8.52 and 22.3 microg ml(-1), respectively. In the wedge preparation, moxifloxacin produced a concentration-dependent prolongation of the action potential duration, QT interval, and the time between peak and end of the T wave, an indicator for transmural dispersion of repolarization. Phase 2 early after-depolarizations were observed in one of five experiments at 30 microM and five of five experiments at 100 microM. The arrhythmogenic potential was also concentration-dependent, and 100 microM ( approximately 18-fold above the typical unbound Cmax exposure in clinical usage) appeared to have a high risk of inducing torsade de pointes (TdP). Our data indicated a good correlation among the concentration-response relationships in the three preclinical models and with the available clinical data. The lack of TdP report by moxifloxacin in patients without other risk factors might be attributable to its well-behaved pharmacokinetic profile and other dose-limiting effects.

The impact of mechanical ventilation on the moxifloxacin treatment of experimental pneumonia caused by Streptococcus pneumoniae.

OBJECTIVE: Streptococcus pneumoniae is a leading cause of community-acquired pneumonia and is responsible for early-onset ventilator-associated pneumonia as well. In intensive care units, community-acquired pneumonia is still associated with a mortality rate of up to 30%, especially when mechanical ventilation is required. Our objective was to study to what extent MV could influence the efficacy of moxifloxacin in a rabbit model of pneumonia. DESIGN: Prospective experimental study. SETTING: University hospital laboratory. SUBJECTS: Male New Zealand White rabbits (n = 75). INTERVENTIONS: S. pneumoniae (16089 strain; minimal inhibitory concentration for moxifloxacin = 0.125 mg/L) was instilled intrabronchially. Four hours later, a human-like moxifloxacin treatment was initiated in spontaneously breathing (SB) and mechanically ventilated (MV) animals. Untreated rabbits were used as controls. Survivors were killed 48 hrs later. Pneumonia was assessed and moxifloxacin pharmacokinetics were analyzed. MEASUREMENTS AND MAIN RESULTS: Moxifloxacin treatment was associated with an improvement in survival in the SB animals (13 of 13 [100%] vs. eight of 37 [21.6%] controls). The survival rate was less influenced by treatment in MV rabbits (seven of 15 [46.1%] vs. one of eight [12.5%] controls). The lung bacterial burden was greater in MV compared with SB rabbits (5.1 +/- 2.4 vs. 1.6 +/- 1.4 log10 colony-forming units/g, respectively). Nearly all the untreated animals presented bacteremia as reflected by a positive spleen culture. No bacteremia was found in SB animals treated with moxifloxacin. In contrast, three of 13 (23.1%) moxifloxacin-treated and MV animals had positive spleen cultures. The apparent volume of distribution of moxifloxacin was lower in MV compared with SB rabbits. CONCLUSIONS: In our model of moxifloxacin-treated S. pneumoniae pneumonia, mechanical ventilation was associated with a higher mortality rate and seemed to promote bacterial growth as well as systemic spread of the infection. In addition, the volume of distribution of moxifloxacin was reduced in the presence of mechanical ventilation. Although the roles of factors such as anesthesia, paralysis, and endotracheal tube insertion could not be established, these results suggest that mechanical ventilation may impair host lung defense, rendering antibiotic therapy less effective.