Sensitive high-performance liquid chromatographic determination of pirenzepine in plasma

A high-performance liquid chromatographic method for the determination of pirenzepine in human plasma is reported using imipramine as an internal standard. The assay has a lower limit of detection of 2.5 ng/ml. The calibration function is found to be linear in the range from 5 ng/ml up to at least 100 ng/ml. Two sets of chromatographic conditions are described, which provide different chromatographic selectivities for the separation of the compounds of interest from other material present in a sample.     

Effective high-performance liquid chromatographic determination of glafenine in plasma: pharmacokinetic application

A high-performance liquid chromatographic method for an effective determination of glafenine and its main metabolite, glafenic acid, is described. The assay involves separate extraction procedures for glafenine and for its metabolite, but the same internal standard (floctafenine) and the same chromatographic conditions (including a 5-micron C8 column, a quaternary solvent mixture of water-acetonitrile-diethylamine-acetic acid and an ultraviolet detector set at 360 nm). For 1 ml of plasma, the detection limit is 0.05 mg/l for glafenine and 0.25 mg/l for glafenic acid. Compared with previously described techniques, this assay uses a very low glafenine linearity range, which allows the true pharmacokinetics of this drug to be described for the first time.     

Isocratic high-performance liquid chromatographic determination of plasma adenosine

Summary Due to manifold physiological and cardioprotective actions of adenosine, the demand for a simple but accurate method to determine its concentration in plasma is increasing. The aim of this study was firstly to develop a simple isocratic method instead of the gradient elution or peak-shifting techniques used earlier and secondly to check conflicting data on the composition of stop-solution, added to the sample in order to prevent changes in adenosine concentration. Isocratic elution improved signal to noise ratio and concentrations of 100 mol L^–1 dipyridamole and 2.5 mol L^–1 erythro-9(2-hydroxy-3-nonyl)adenine in the blood sample effectively prevented both adenosine formation and degradation, even without the use of a 5-ecto-nucleotidase inhibitor. Lowering the concentration of dipyridamole to 25 mol L^–1 caused more than a tenfold increase of adenosine concentration in two out of five cases and even 100 mol L^–1 dipyridamole alone is not sufficient to inhibit adenosine deaminase in blood samples.     

Sensitive high-performance liquid chromatographic determination of arbidol, a new antiviral compound, in human plasma

A highly sensitive and selective HPLC method was developed and validated for the determination of arbidol in human plasma. The method involves the liquid–liquid extraction of drug and internal standard from plasma with tert.-butyl methyl ether followed by evaporation and reconstitution in mobile phase. UV detection was done at 315 nm. The limit of quantification for arbidol in plasma was 0.005 μg/ml. Linearity in plasma was proven over the whole calibration range (10.2–0.005 μg/ml). The method was validated according to GLP guidelines and its suitability was demonstrated by analysis of samples from a pharmacokinetic study.     

Sensitive high-performance liquid chromatographic assay for the determination of eugenol in body fluids

The high-performance liquid chromatographic assay described permitted a simple, rapid, sensitive, selective and precise quantitative determination of eugenol in body fluids (serum, urine and bile) without derivatization. Amounts in the range 0.02-100 micrograms of eugenol per millilitre of body fluid were determined with intra-assay coefficients of variation below 4% (3.72-1.13%). The short analysis time for each sample and the selectivity even at low concentrations made this assay suitable for pharmacokinetic studies. Eugenol undergoes a pronounced first-pass effect; in serum, unconjugated eugenol was not detected after an oral dose of 150 mg. The kinetics of eugenol conjugates were measured. More than 80% of the dose was excreted within 6 h after oral administration.     

An improved high-performance liquid chromatographic determination of chlorpropamide in human plasma

Summary Samples were extracted with dichloromethane and the organic layer evaporated to dryness. The residue was dissolved in methanol, and 10 μl aliquot injected onto the column. Tolbutamide was used as the internal standard for chlorpropamide. The UV detector response was linear over the range 0–200 μg ml⁻¹ with a correlation coefficient of 0.999; detection limit: 0.002 μg ml⁻¹. Within-day and between-day assay variation was generally ≤7%. No interference from endogenous constituents was observed. The utility of the method was demonstrated by determining chlorpropamide in samples from six healthy volunteers following a single oral dose of 250 mg. The procedure is simple and requires small volumes of plasma.     

Improved liquid chromatographic tandem mass spectrometric determination and pharmacokinetic study of glimepiride in human plasma

An improved liquid chromatographic tandem mass spectrometric method for the determination of glimepiride in human plasma has been developed and fully validated. The article describes in detail the bioanalytical procedure and summarizes the validation results obtained. The samples were extracted using liquid--liquid extraction with a mixture of 1-chlorobutane-isopropanol-ethyl acetate (88:2:10, v/v/v). The chromatographic separation was performed on a reversed-phase Hypersil ODScolumn (250 x 4.6 mm i.d.; 5 microm particle size) using a mobile phase consisting of formic acid 0.05 M-acetonitrile (28:72, v/v), pumped at a flow rate of 0.3 ml min(-1) heated to 25 degrees C. The analytes were detected using an API 3000 triple quadrupole mass spectrometer with positive electrospray ionization in multiple reaction monitoring mode. Tandem mass spectrometric detection enabled the quantitation of glimepiride down to 0.50 ng mL(-1). Calibration graphs were linear (r better than 0.998, n=1), in concentration range 0.50--1000 ng mL(-1), and the intra- and inter- day RSD values were less than 10.37 and 11.55% for glimepiride. The method was successfully applied to a kinetic study in order to assess the main pharmacokinetic parameters of glimepiride.     

Simple high-performance liquid chromatographic method for the determination of tetramethylpyrazine phosphate in very small volumes of dog plasma: application to a pharmacokinetic study

A rapid and sensitive high-performance liquid chromatographic (HPLC) method is developed for the determination of tetramethylpyrazine phosphate, an antiplatelet aggregation agent, in 100 microL of dog plasma. Sample preparations are carried out by deproteinization with an internal standard (carbamazepine) solution in acetonitrile. An aliquot of the supernatant (20 microL) is directly injected into an HPLC apparatus with methanol-phosphate buffer (0.01M, pH 3.0) (62:38, v/v) as the mobile phase at a flow rate of 1.0 mL/min. Separation is performed with a C18 column at 30 degrees C. The peak is detected using a UV detector set at 279 nm. The capacity factors are 1.48 for tetramethylpyrazine phosphate and 2.09 for carbamazepine, with a total run time of 10 min. The calibration curve is linear in the 0.2-50-microg/mL range. The limit of detection is 0.05 microg/mL. Mean recoveries are 92.6-98.1%. The within- and between-day variation coefficients are less than 4.9% and 7.5%, respectively. The present method has been successfully used to provide pharmacokinetic data after oral administration of tetramethylpyrazine phosphate pulsincap capsules and immediate-release tablets to dogs.     

Determination of neomycin in plasma and urine by high-performance liquid chromatography. Application to a preliminary pharmacokinetic study.

A reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the determination of neomycin in plasma and urine. The plasma was deproteinated with trichloroacetic acid and centrifuged. The supernatant was mixed with ion-pair concentrate and centrifuged again. The resultant supernatant was analyzed by HPLC. Urine was centrifuged to remove debris, if any, mixed with ion-pair concentrate and analyzed directly by HPLC. The HPLC conditions consisted of an ion-pairing mobile phase, a reversed-phase column, post-column derivatization with o-phthalaldehyde (OPA) reagent and fluorescence detection. The overall average recovery of neomycin was 97 and 113% from plasma spiked at 0.25-1.0 micrograms/ml, using standard curves prepared in plasma extract and in water, respectively, and 94% for urine spiked at 1-10 micrograms/ml using a standard curve prepared in water. The method was used to detect neomycin in plasma and urine obtained from animals injected intramuscularly with neomycin. Various pharmacokinetic parameters of neomycin were also determined from its profile of plasma concentration versus time.