Enantioseparation of ofloxacin in urine by capillary electrokinetic chromatography using charged cyclodextrins as chiral selectors and assessment of enantioconversion

Enhanced antibacterial activity of levofloxacin/hydroxypropyl-β-cyclodextrin inclusion complex: In vitro and in vivo evaluation

Levofloxacin is the levo-enantiomer of ofloxacin (a fluoroquinolone class of antibacterial drug). Cyclodextrins (CDs) including hydroxypropyl-β-cyclodextrin (HPβCD) are generally used as a chiral selector for the enantioseparation of some drugs including levofloxacin or as a drug/food nanocarrier for the efficacy improvement of many pharmaceuticals. We hypothesized that the cyclodextrin inclusion is potentially able to further improve the antibacterial activity of levofloxacin. To test this hypothesis, the levofloxacin/HPβCD inclusion complex was prepared by the freeze-drying method and characterized by phase solubility diagram, differential scanning calorimetry (DSC), X-ray diffractometry (XRD), UV-Vis spectrophotometer, and ¹H NMR spectroscopy, confirming the successful HPβCD inclusion of levofloxacin. The in vitro antibacterial effects of HPβCD, levofloxacin, and the levofloxacin/HPβCD inclusion complex against four different bacterial strains in liquid media and on agar plates were determined/compared (an MIC₉₀ of 0.5-1.0 μg/mL for the inclusion complex compared with that of 1.0-2.0 μg/mL for free levofloxacin in liquid). Moreover, the in vivo antibacterial effects of levofloxacin and levofloxacin/HPβCD inclusion complex were tested by using a skin scald model in mice infected with Staphylococcus aureus, and decreased amounts of both bacteria and leukocytes were detected in scalded skin after the inclusion complex treatment. The data revealed that the levofloxacin/HPβCD inclusion complex had an enhanced antibacterial activity compared with free levofloxacin. It implies that cyclodextrins (e.g. HPβCD) may have a beneficial role when using as a chiral selector or as a drug nanocarrier for levofloxacin and that the levofloxacin/HPβCD inclusion complex has the potential of being developed into a pharmaceutical for antibacterial therapies.

Chiral separation of quinolones by liquid chromatography and capillary electrophoresis

The quinolones are derivatives of oxoquinolines and mostly known for their antibacterial and antiviral activities. Many quinolones are chiral compounds having asymmetric centers and important due to their enantioselective biological activities. In order to study the biological activities of quinolone enantiomers, to control the manufacturing of homochiral drugs and to prepare necessary quantities of pure enantiomers for preclinical or clinical trials, respective chiral separation methods are urgently needed. In this context, the present review discusses chromatographic and electrophoretic methods for the enantioseparation of chiral quinolones and provides some useful information on their physical and pharmaceutical properties. The drawbacks of currently used techniques are revealed and ways to overcome them are outlined. Moreover, recommendations for an optimal choice of a separation protocol are given.

Methods for the analysis of fluoroquinolones in biological fluids

Methods for the analysis of ten selected fluoroquinolone antibiotics in biological fluids are reviewed. Approaches for sample preparation, detection methods, limits of detection and quantitation, and recovery information are provided for both single analyte and multi-analyte fluoroquinolone methods.

Chiral separation of four fluoroquinolone compounds using capillary electrophoresis with hydroxypropyl-β-cyclodextrin as chiral selector

A capillary zone electrophoresis (CZE) investigation on the enantiomeric separation of lomefloxacin, gatifloxacin, pazufloxacin and ofloxacin was undertaken. Resolution of the enantiomers was achieved using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as the chiral selector. Parameters influencing separation include cyclodextrin concentration, separational potential, pH and organic additive are discussed. A buffer consisting of 70 mM phosphate and 40 mM HP-beta-CD at pH 3.96 was found to be highly efficient for the separation of lomefloxacin, at pH 3.90 for gatifloxacin, at pH 5.04 for pazufloxacin and at pH 2.16 for ofloxacin. To the best of our knowledge, this is the first report on the enantiomeric resolution of lomefloxacin and gatifloxacin applying CE.

Hydrophilic interaction liquid chromatography–tandem mass spectrometry for the determination of levofloxacin in human plasma

A rapid, sensitive and selective hydrophilic interaction liquid chromatography-tandem mass spectrometric (HILIC-MS/MS) method for the determination of levofloxacin in human plasma was developed. Levofloxacin and ciprofloxacin (internal standard) were extracted from human plasma with dichloromethane and analyzed on an Atlantis HILIC Silica column with the mobile phase of acetonitrile-ammonium formate (100 mM, pH 6.5) (82:18 v/v). The analytes were detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r>0.999) over the concentration range of 10.0-5000 ng/ml. The lower limit of quantification for levofloxacin was 10.0 ng/ml using 20 microl plasma sample. The coefficient of variation and relative error for intra- and inter-assay at four QC levels were 2.9-7.8% and -7.3% to -2.2%, respectively. The recoveries of levofloxacin and ciprofloxacin were 55.2% and 77.3%, respectively. This method was successfully applied to the pharmacokinetic study of levofloxacin in humans.

Enantiomeric purity assay of moxifloxacin hydrochloride by capillary electrophoresis

A capillary electrophoresis method for determining the enantiomeric purity of moxifloxacin hydrochloride in drug substance and ophthalmic/otic drug products was developed and validated. Because moxifloxacin hydrochloride has two chiral centers, the existence of four different isomers is possible. The method was capable of separating moxifloxacin hydrochloride, which is the S,S-isomer, from its potential chiral degradation products, which are the R,R-enantiomer, the R,S-diastereomer, and the S,R-diastereomer. The separation was carried out at 20 degrees C in a 50 microm x 40 cm fused-silica capillary with an applied voltage of -13 kV using a 12.5 mM TEA phosphate buffer (pH 2.5) containing 5% highly-sulfated gamma-cyclodextrin (HS-gamma-CD) and 6% acetonitrile. The detection wavelength was 295 nm. The method was validated with respect to its specificity, linearity, range, accuracy, and precision in the expected range of occurrence for the isomeric impurities (0.05-5%). The method was used to investigate whether racemization was a potential degradation pathway for the drug substance, both in the solid state and in solution.

Comprehensive strategy for chiral separations using sulfated cyclodextrins in capillary electrophoresis

This review focuses on the emerging role of sulfated cyclodextrins in the capillary electrophoretic (CE) separation of chiral analytes. Since being introduced as enantioselective agents for CE in 1995, these anionic additives have continued to demonstrate remarkable application universality. The broad spectrum of chiral compounds successfully separated using this approach includes acidic, basic, neutral, and zwitterionic species. This impressive array of analyte structures is derived from a growing diversity of compound classes including pharmaceuticals, plant extracts, biomarkers, herbicides, alkaloids, fungicides, and metal ions. Moreover, literature reports highlight the minimal optimization required to achieve a successful separation. Based on these findings, sulfated cyclodextrins appear to be well suited for the development of a more universal, comprehensive separation strategy for chiral compounds. This review explores this proposition by beginning with the structure and migration properties of sulfated cyclodextrins, using applications to highlight the separating power of this technique and ending with a pragmatic, comprehensive separation strategy.

Pharmacokinetic study of levofloxacin in rat blood and bile by microdialysis and high-performance liquid chromatography

The aim of this study was to develop a rapid and sensitive method for the simultaneous determination of unbound levofloxacin in rat blood and bile using high-performance liquid chromatography coupled with microdialysis for further pharmacokinetic study. Microdialysis probes were simultaneously inserted into the jugular vein toward the right atrium and the bile duct of male Sprague-Dawley rats for biological fluid sampling after administration of levofloxacin 3 mg/kg through the femoral vein. Levofloxacin and dialysates were separated using a Merck LiChrospher reversed-phase C18 column maintained at ambient temperature. The mobile phase was comprised of acetonitrile-1 mM 1-octanesulfonic acid (40:60, v/v, pH 3.0 adjusted with orthophosphoric acid). The fluorescence response for levofloxacin was observed at excitation and emission wavelengths of 292 and 494 nm, respectively. The detection limit of levofloxacin was 50 ng/ml. Intra-day and inter-day precision and accuracy of levofloxacin measurements fell well within the predefined limits of acceptability. The disposition of levofloxacin in the blood and bile fluid suggests that there was rapid exchange and equilibration between the blood and hepatobiliary systems, and the plasma level of levofloxacin was greater than that of the bile. Thus, levofloxacin undergoes hepatobiliary excretion but might not be related to the P-glycoprotein transport system.

Selected fundamental aspects of chiral electromigration techniques and their application to pharmaceutical and biomedical analysis

While capillary electrophoresis has been established as a major enantioseparation technique within the last decade, the potential of capillary electrochromatography is still studied extensively. This review summarizes recent applications of electromigration techniques with regard to the enantioseparation of chiral drugs. The first part discusses the general aspects of migration models and the enantiomer migration order. The application of capillary electrophoresis to chiral pharmaceutical analysis considers recent literature on: (1) chiral resolutions of non-racemic mixtures of enantiomers for the development of assays and the determination of the stereochemical purity of the drugs, (2) chiral separations of compounds in pharmaceutical formulations and products, and (3) enantioseparations of drugs in biological samples. A shorter section devoted to chiral electrochromatography discusses some fundamental aspects as well as the application to the chiral analysis of drugs including bioanalysis.