Determination of linezolid in human serum by reversed-phase high-performance liquid chromatography with ultraviolet and diode array detection

A high-performance liquid chromatographic (HPLC) method with UV and DAD detection for the quantitative determination of linezolid in human serum was developed in present work. Chromatography was carried out by reversed-phase technique on a RP-18 column with a mobile phase composed of 50 mM phosphate buffer and acetonitrile (76 : 26, v/v), adjusted to pH 3.5 with orthophosphoric acid. Serum samples were deproteinized with methanol centrifuged and then, the supernatant was analyzed using HPLC procedure. No interference was observed at the retention times of linezolid from blank serum or ten commonly used antibiotics. A concentration range from 0.50 to 30.0 g/mL was utilized to construct calibration curves. The lower limit of detection was determined to be 0.1 μg/mL of serum for both detectors. The lower limit of quantification of 0.25 μg/mL (CV = 2.6%) was established for determination using HPLC-UV and 0.5 μg/mL (CV = 5.42%) for HPLC-DAD. The recovery of linezolid was approximately 100%. Intra-day accuracy ranged from 0.97 to 12.63% and 0.74 to 10.85% for HPLC-UV and HPLC-DAD method, respectively. Intra-day precision was less than 4.69% for HPLC-UV and less than 5.42% for HPLC-DAD method. Tests confirmed the stability of linezolid in serum during three freeze-thaw cycles and during long-term storage of frozen serum for up to 6 weeks; in extracts it was stable in the HPLC autosampler over 24 h. Statistical analysis by Student's t-test showed no significant difference between the results obtained by these two methods. In summary, these methods will be used and adapted for infected patients in intensive care unit, to determine linezolid serum concentrations in order to know the pharmacokinetic profiles of linezolid

Determination of linezolid in human serum by reversed-phase high performance liquid chromatography with ultrafiolet and diode array detection

A high-performance liquid chromatographic (HPLC) method with UV and DAD detection for the quantitative determination of linezolid in human serum was developed in present work. Chromatography was carried out by reversed-phase technique on a RP-18 column with a mobile phase composed of 50 mM phosphate buffer and acetonitrile (76 : 26, v/v), adjusted to pH 3.5 with orthophosphoric acid. Serum samples were deproteinized with methanol centrifuged and then, the supernatant was analyzed using HPLC procedure. No interference was observed at the retention times of linezolid from blank serum or ten commonly used antibiotics. A concentration range from 0.50 to 30.0 g/mL was utilized to construct calibration curves. The lower limit of detection was determined to be 0.1 μg/mL of serum for both detectors. The lower limit of quantification of 0.25 μg/mL (CV = 2.6%) was established for determination using HPLC-UV and 0.5 μg/mL (CV = 5.42%) for HPLC-DAD. The recovery of linezolid was approximately 100%. Intra-day accuracy ranged from 0.97 to 12.63% and 0.74 to 10.85% for HPLC-UV and HPLC-DAD method, respectively. Intra-day precision was less than 4.69% for HPLC-UV and less than 5.42% for HPLC-DAD method. Tests confirmed the stability of linezolid in serum during three freeze-thaw cycles and during long-term storage of frozen serum for up to 6 weeks; in extracts it was stable in the HPLC autosampler over 24 h. Statistical analysis by Student's t-test showed no significant difference between the results obtained by these two methods. In summary, these methods will be used and adapted for infected patients in intensive care unit, to determine linezolid serum concentrations in order to know the pharmacokinetic profiles of linezolid

Validation of LC/MS/MS method for assessment of the "in vitro" activity of the selected rat cytochrome P450 isoenzymes : application to early drug metabolism screening

A sensitive and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for simultaneous determination of seven metabolites of CYP450 model substrates (acetaminophen, 4-hydroxytolbutamide, 4í-hydroxymephenytoin, 1-hydroxybufuralol, 6-hydroxychlorzoxazone, 1í- and 4í-hydroxymidazolam) in rat liver microsomes was developed. The assay used Kinetex analytical column and a gradient mobile phase consistent of acetonitrile and water with addition of 0.1% formic acid. The analysis was performed in selected reaction monitoring (SRM) mode both in positive and negative (for 6-hydroxychlorzoxazone) mode. The method was validated over the concentration ranges of 10-2000 ng/mL for 4í-hydroxymephenytoin and 4-hydroxytolbutamide, 50-2000 ng/mL for 1-hydroxybufuralol and 25-2000 ng/mL for the rest of the analytes. The intra- and inter-day precision (2-12%) and accuracy (93-119%) were within the limits set by the FDA and EMA guidelines. The developed method was successfully applied to assess the activity of selected CYP450 isoenzymes in rat liver microsomes after addition of ketoconazole

Validation of LC/MS/MS method for assessment of the "in vitro" activity of selected rat cytochrome P450 isoenzymes : application to early drug metabolism screening

A sensitive and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for simultaneous determination of seven metabolites of CYP450 model substrates (acetaminophen, 4-hydroxytolbutamide, 4'-hydroxymephenytoin, 1-hydroxybufuralol, 6-hydroxychlorzoxazone. 1'-and 4-hydroxymidazolam) in rat liver microsomes was developed. The assay used Kinetex analytical column and a gradient mobile phase consistent of acetonitrile and water with addition of 0.1\% formic acid. The analysis was performed in selected reaction monitoring (SRM) mode both in positive and negative (for 6-hydroxychlorzoxazone) mode. The method was validated over the concentration ranges of 10-2000 ng/mL for 4-hydroxymephenytoin and 4-hydroxytolbutamide, 50-2000 ng/mL for 1-hydroxybufuralol and 25-2000 ng/mL for the rest of the analytes. The intra- and inter-day precision (2-12%) and accuracy (93-119%) were within the limits set by the FDA and EMA guidelines. The developed method was successfully applied to assess the activity of selected CYP450 isoenzymes in rat liver microsomes after addition of ketoconazole

Binding of 1-[3-(4-tert-butyl-phenoxy)propyl]piperidine, a new non imidazole histamine H3 receptor antagonist to bovine serum albumin

The degree of binding of a drug to plasma proteins has a significant effect on its distribution, elimination, and pharmacological effect since only the unbound fraction is available for distribution into extra-vascular space. The binding of DL76 (1-[3-(4-tert-butyl-phenoxy)propyl]piperidine) to bovine serum albumin (BSA) was studied in vitro by equilibrium dialysis at 37OC and pH 7.4 over the concentration range of 0.32ñ317.18 μM and at a physiological protein concentration of 602 μM. Drug concentrations were determined by validated LC/MS/MS method. Nonlinear regression analyses of the data pointed to a single class of binding sites (m = 1) with a dissociation constant of DL76 equal 49.20 μM. Scatchard plot concave-down curve might indicate positive cooperativity, which was confirmed by the Hill plot with the slope higher than one

Determination of "in vitro" metabolism of a new non-imidazole histamine H3 receptor antagonist 1-[3-(4-tert-butylphenoxy) propyl]piperidine

Early understanding of the pharmacokinetics of drug candidates is essential during the evaluation of drug development process. DL76 1-[3-(4-tert-butylphenoxy)propyl]piperidine is a novel promising non-imidazole H3 receptor antagonist. The presented study was undertaken to compare with each other the predicted hepatic clearance values of DL76 calculated, using two most common mathematical models ìwell-stirredî and ìparallel tubeî, based on the data obtained in in vitro experiments. The metabolic intrinsic clearance of DL76 equaled to 0.4848 mL/min/mg protein was scaled up and the values of hepatic clearance estimated from ìwellstirredî and ìparallel tubeî models were 55.47 mL/min/kg and 58.80 mL/min/kg, respectively. They were further compared with pharmacokinetic parameters calculated based on the concentration-time profile obtained following intravenous administration of DL76 to rats at the dose of 6 mg/kg. The estimated systemic serum clearance value of 144.5 mL/h/kg and blood clearance value of 81.17 mL/min/kg indicate the potential extrahepatic metabolism of the investigated compound. This study demonstrates the utility of rat liver microsomes for the prediction of DL76 hepatic clearance

LC–MS–MS Method for the Analysis of New Non-Imidazole Histamine H3 Receptor Antagonist 1-[3-(4-tert-Butylphenoxy)propyl]piperidine in Rat Serum—Application to Pharmacokinetic Studies

A sensitive and specific liquid chromatography electrospray ionisation–tandem mass spectrometry method for determination of new non-imidazole histamine H3 receptor antagonist 1-[3-(4-tert-butylphenoxy)propyl]piperidine (DL76) in rat serum has been developed and validated. Chromatography was performed on a XBridge™ C18 analytical column (2.1 × 30 mm, 3.5 µm, Waters, Ireland) with gradient elution using a mobile phase containing acetonitrile and water with an addition of 0.1% of formic acid. Detection was achieved by an Applied Biosystems MDS Sciex (Concord, Ontario, Canada) API 2000 triple quadrupole mass spectrometer. Electrospray ionization (ESI) was used for ion production. The limit of detection in the SRM mode was found to be 0.5 ng mL−1. The limit of quantification was 1 ng mL−1. The precision and accuracy for both intra- and inter-day determination of DL76 ranged from 1.65 to 15.09% and from 88.74 to 113.43%. The results of this analytical method validation allow to carry out pharmacokinetic studies in rats. The method was used for the pilot study of the pharmacokinetic behavior of DL76 in rats after intravenous administration