Simultaneous determination of 5-fluorouracil and its active metabolites in serum and tissue by high-performance liquid chromatography

In order to observe the biodistribution of 5-fluorouracil (5-FU) and its main metabolites in different kinds of tissue (tumor, liver, kidney, spleen, mucosa, lungs, heart, peritoneum, pancreas) and serum according to various novel application forms, a simple and rapid method for the simultaneous determination of 5-FU and its active metabolites 5-fluorouridine (5-FUrd) and 5-fluoro-2'-deoxyuridine (5-FdUrd) has been established. Proteins in serum and tissue samples were precipitated by perchloric acid after addition of the internal standard 5-bromouracil. The compounds were separated using an ODS Hypersil (5 microm) column and detected by UV absorbance (254 nm). Specificity, linearity, reproducibility, intermediate precision and accuracy of the method were established. The lower limit of quantitation (LOQ) for the compounds in serum and various tissue samples was determined. Data on the recovery of the compounds and the internal standard are provided.

Determination of warfarin in the yolk and the white of hens' eggs by reversed-phase high-performance liquid chromatography

A procedure for the determination of warfarin, an anticoagulant rodenticide, in the white and the yolk of hens' eggs, using reversed-phase high-performance liquid chromatography is described. Liquid chromatography was performed on an octadecylsilane cartridge using methanol and ammonium acetate triethylamine buffer as the mobile phase, with UV detection at 281 nm. Samples (5 g) were analysed after liquid-phase extraction using a mixture of acetone and diethyl ether. Linearity, precision and accuracy of the method were determined in the range of 0.5-8.0 microg. Limits of quantitation for warfarin in the white and the yolk were 0.020 and 0.015 microg/g, respectively. Mean recoveries of warfarin from spiked white and yolk samples were 84.6 and 87.4%, respectively. The analytical method was applied to a fourteen-day experimental study conducted in laying hens that had been orally dosed with warfarin.

Validation parameters for a novel biosensor assay which simultaneously measures serum concentrations of a humanized monoclonal antibody and detects induced antibodies

This report documents the validation of an assay using BIAcore 2000 that, with a single injection of mouse serum, allows the quantitation of a humanized monoclonal antibody and can also detect the presence of antibodies directed against this humanized antibody. The important components required for the validation of biosensor assays including precision, accuracy, linearity, stability of the immobilized ligand, specificity and sensitivity are addressed. The tandem assay that is used as a model for biosensor validations is accomplished by flowing each sample across the surface of two flowcells in sequence. The first flowcell has the antigen that the humanized mAb was generated against immobilized while the humanized mAb itself is immobilized on the second flowcell. The quantitation component of this assay is precise and accurate with a limit of quantitation of 1 microg/ml in mouse serum samples. Any antibodies directed against the humanized mAb can be detected and also characterized as to isotype. This unique assay can be performed with as little as 10 microl of serum which is then diluted ten-fold prior to analysis. The small sample requirement allows analysis of individual mouse serum samples rather than requiring the use of pooled samples from multiple mice. A further advantage of this assay is the automation capability which allows unattended operation.

An enzyme immunoassay for rat growth hormone: validation and application to the determination of plasma levels and in vitro release

A competitive enzyme immunoassay for rat growth hormone (rGH) has been developed using polyclonal anti-rGH antibodies and an acetylcholinesterase (EC 3.1.1.7.) enzymatic tracer coupled covalently with rGH. The assay was performed in 96-well microtiter plates coated with rabbit polyclonal anti-goat immunoglobulin antibodies. Molecular sieve filtration and Western blot analysis revealed a single immunoreactive peak for rat plasma or pituitary extracts. Cross-reactivity with other rat pituitary hormones or human GH was less than 1%. Assay of samples in a concentration range of 0.7 to 69 ng/ml by enzyme immunoassay and radioimmunoassay were well correlated (r = 0.87 and 0.85 respectively for plasma and culture medium samples). Intra- and inter-assay variations in plasma were 4 (n = 24) and 14% (n = 9) respectively. Minimal detectable amounts of rGH were 0.6 ng/ml. A two-site immunometric assay also developed with the same antibodies allowed a detection threshold of 0.25 ng/ml.

Simultaneous determination of amphetamine and its analogs in human whole blood by gas chromatography-mass spectrometry

A sensitive and specific gas chromatography-mass spectrometry (GC-MS) method for the determination of amphetamine (AM), methamphetamine (MA), methylenedioxyamphetamine (MDA), methylenedioxymethamphetamine (MDMA) and methylenedioxyethylamphetamine (MDEA) in whole blood was designed, using the respective pentadeuterated analogs of the analytes as internal standards (I.S.). After alkalinisation of blood samples, the amphetamines were extracted using diethyl ether, derivatized with heptafluorobutyric anhydride, then purified by successive washings with deionized water and 4% NH4OH. Extraction recoveries were 85.2% for AM, 90.9% for MA, 76.5% for MDA, 84.1% for MDMA and 63.6% for MDEA. Chromatographic separation was performed on a non-polar 30 m x 0.32 mm HP 5 MS capillary column using a temperature program. Detection was carried out in the electron-impact, selected ion-monitoring mode, using three mass-to-charge ratios for each analyte and one for each I.S. Limits of detection ranged from 0.5 to 8 ng/ml and limits of quantification were 10 ng/ml for AM, MDMA and MDEA; 20 ng/ml for MA; and 50 ng/ml for MDA. The method was linear from this limit up to 1000 ng/ml for all analytes, with good intra-assay precision and good intermediate precision and accuracy over these ranges. There was no interferences from other sympathomimetic drugs such as ephedrine, norephedrine or methoxyphenamine. This method is thus suitable for clinical and forensic toxicology, as well as for doping control.

A comprehensive model for enrofloxacin to ciprofloxacin transformation and disposition in dog

The pharmacokinetics of enrofloxacin and ciprofloxacin, its major active metabolite, were determined in dog after oral and intravenous administrations of enrofloxacin and intravenous infusion of ciprofloxacin. A comprehensive model of enrofloxacin and ciprofloxacin disposition was constructed to investigate the extent of enrofloxacin to ciprofloxacin transformation and the influence of the hepatic first-pass effect on the parent compound oral bioavailability. Plasma levels were measured using a validated HPLC method. Enrofloxacin and ciprofloxacin plasma concentration data were fitted simultaneously using a set of differential equations describing a six-compartment model (two compartments for each analyte, one for the liver, and one for the intestinal tract); it was assumed that only a fraction of enrofloxacin was metabolized to ciprofloxacin and that this conversion only occurred in the liver. The fitted parameters obtained from the model were used to calculate plasma clearances (0.729 +/- 0.212 L/h/kg for enrofloxacin, 0.468 +/- 0.094 L/h/kg for ciprofloxacin), distribution volumes (2.45 +/- 0.49 L/kg for enrofloxacin, 1.92 +/- 0.33 L/kg for ciprofloxacin), mean residence times (3.47 +/- 0.78 h for enrofloxacin, 4.20 +/- 0.82 h for ciprofloxacin), and the fractions of enrofloxacin metabolized to ciprofloxacin after intravenous and oral administrations of enrofloxacin. It was shown that enrofloxacin was largely metabolized to ciprofloxacin and that the fractions of metabolized enrofloxacin were similar after intravenous and oral administrations of enrofloxacin (40.44 +/- 10.08 and 40.17 +/- 8.33%, respectively), the hepatic first-pass effect being low (7.15 +/- 1.99%).

Determination of N,N',N"-triethylenthiophosphoramide in biological samples using capillary gas chromatography

A sensitive assay for the determination of N,N',N"-triethylenthiophosphoramide (thioTEPA) in microvolumes of human plasma and urine has been developed. ThioTEPA was analysed using gas chromatography with selective nitrogen-phosphorus detection, after extraction with ethyl acetate from the biological matrix. Diphenylamine is the internal standard. The limit of quantitation was 0.1 ng/ml, using only 100 microl of sample; recoveries ranged between 85 and 100% and both accuracy and precision were less than 10%. Using a flame ionisation nitrogen-phosphorus detector, the assay was not linear over the concentration range of 2-1000 ng/ml for plasma and 10-1000 ng/ml for urine. Linearity was accomplished in the range of 1-1000 ng/ml for plasma and urine when a thermionic nitrogen/phosphorous detector was used. The stability of thioTEPA in plasma proved to be satisfactory over a period of 3 months, when kept at -20 degrees C, whereas it was stable in urine for at least 1 month at -80 degrees C. ThioTEPA plasma concentrations of two patients treated with thioTEPA are presented demonstrating the applicability of the assay.

A competitive enzyme hybridization assay for plasma determination of phosphodiester and phosphorothioate antisense oligonucleotides

An enzyme competitive hybridization assay was developed and validated for determination of mouse plasma concentrations of a 15mer antisense phosphodiester oligodeoxyribonucleotide and of two phosphorothioate analogs. Assays were performed in 96-well microtiter plates. The phosphodiester sense sequence was covalently bound to the microwells. The 5'-biotinylated antisense sequence was used as tracer. The principle of the assay involves competitive hybridization of tracer and antisense nucleotide to the solid phase-immobilized sense oligonucleotide. Solid phase- bound tracer oligonucleotide was assayed after reaction with a streptavidin-acetylcholinesterase conjugate, using the colorimetric method of Ellman. As in competitive enzyme immunoassays, coloration was inversely related to the amount of analyte initially present in the sample. The limit of quantification was 900 pM for phosphodiester antisense oligonucleotide using a 100 microl volume of plasma without extraction. Cross-reactivity was negligible after a four base deletion in either the 3'or 5'position. The assay was simple and sensitive, suitable for in vitro screening of oligonucleotide hybridization potency in biological fluids and for measuring the plasma pharmacokinetics of phosphorothioate and phosphodiester sequences.

Quantification of benzocaine and its metabolites in channel catfish tissues and fluids by HPLC

Methods for extraction and gradient HPLC quantification were developed for benzocaine (BZ) and three of its metabolites to be used in conjunction with a reverse isotope technique. The metabolites were p-aminobenzoic acid (PABA), acetyl-p-aminobenzoic acid (AcPABA) and acetylbenzocaine (AcBZ). The matrixes studied were white muscle, red muscle, skin, liver, trunk kidney, head kidney, plasma and the bile of channel catfish. Analytes were validated for each of the compounds at 25 and 100 nmol per sample in the various tissues and fluids. The intraday variability (R.S.D.) was less than 13% in all tissues and fluids except for BZ in the liver. Recoveries varied from matrix to matrix for each analyte. The highest recoveries were obtained from plasma which ranged from 82.8-99.8% depending on the concentration. The average recovery of the compounds from tissues was between 50 and 78%, except for liver where the recovery of PABA and BZ was below 30%. Detection was by UV absorbance at 286 nm and the linear range was 2.5-15 nmol 100 ml-1 for all analytes. The method was selective; no interference peaks coeluted with the analytes.

Quantitative determination of CGP 61755, a protease inhibitor, in plasma and urine by high-performance liquid chromatography and fluorescence detection

A liquid chromatographic assay for the determination of CGP 61755 (I) in plasma and urine is described. A similar method for CGP 53437, another HIV-1 protease inhibitor, has been developed and reported previously. After a deproteinization step, a liquid-liquid extraction is performed. Compound I and the internal standard CGP 55749 (II) are hydrolyzed and the primary amine group derivatized using fluorescamine. Chromatography is achieved by isocratic elution with a mobile phase of 30 mM borax buffer (pH 9)-acetonitrile (58:42, v/v). The derivatives of the compounds I and II fluoresce at 480 nm, on excitation at 395 nm and the retention times under these conditions were approximately 6 and 8 min, respectively. The limit of quantitation (LOQ) which is the lowest concentration of the analyte that can be measured with a coefficient of variation and a deviation from theory of less than 20%, was 15 ng/ml plasma and 20 ng/ml urine. The analyte is stable for at least four months in human plasma and sixteen months in dog plasma samples. Different human plasma sources and three different species (rat, rabbit and dog) were tested and no interference between analyte and plasma constituents was observed.

Bio-analysis of docetaxel and hydroxylated metabolites in human plasma by high-performance liquid chromatography and automated solid-phase extraction

A semi-automated reversed-phase high-performance liquid chromatography (HPLC) method has been developed and validated for the quantification of the novel anticancer drug docetaxel in human plasma. The chromatographic system also separated putative hydroxylated metabolites. A limited validation was performed for the assay of the metabolites while these reference compounds were not available in large quantities. The sample pretreatment of the plasma samples involves a solid-phase extraction (SPE) on Cyano end-capped columns. 2'-Methylpaclitaxel was used as internal standard. An APEX-octyl column (150 x 4.6 mm I.D.; particle size 5 microns) was used with acetonitrile-0.02 M ammonium acetate buffer pH 5 mixture as the mobile phase. UV detection was performed at 227 nm. In patient samples hydroxylated docetaxel metabolites were detected and quantified by using the docetaxel calibration curve. The accuracies and precisions of the assay fall within +/- 15% for all quality control samples and within +/- 20% for the lower limit of quantitation, which was 10 ng/ml using 1.00 ml of sample for both the parent drug and its metabolites. The overall recovery of the sample pretreatment procedure for docetaxel was 78.0% +/- 5.8% anc 84.8% +/- 3.1% for the internal standard 2'-methylpaclitaxel. Docetaxel was found to be stable in human plasma at -30 degrees C for at least 6 months. At ambient temperature docetaxel was stable for at most 15 h in human plasma.

High-performance liquid chromatographic assay for thiopental in human plasma. Application to pharmacokinetic studies

A simple assay method for the measurement of thiopental by reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet absorbance detection was developed. The method involved a protein precipitation with methanol. Carbamazepine was used as internal standard. The mobile phase was acetonitrile-water (32:62, v/v). The elution was isocratic and the column temperature was ambient. Linear detection response was obtained for concentrations ranging from 1-100 microg ml(-1). Recovery from plasma averaged 88%. Precision, expressed as coefficient of variation (%), was in the range of 0.2-8%. Percent recovery was at least 93%. Stability studies showed that plasma samples should be processed as promptly as possible. This method has been used in therapeutic monitoring and for the determination of pharmacokinetic parameters of thiopental in patients treated with a high dose over a long time to decrease intracranial pressure.

High-performance liquid chromatographic assay for methyl-beta-cyclodextrin in plasma and cell lysate

This paper describes a high-performance liquid chromatographic method with fluorescence detection for the analysis of methyl-beta-cyclodextrin (MEBCD) in plasma and cell lysate, after in situ complexation with 1-naphthol. The size-exclusion HPLC column packed with TSK 3000 SW gel, was equilibrated with an eluent mixture composed of methanol and purified water (2:98, v/v) containing 10(-4) M 1-naphthol as a fluorophore. The detection is based on fluorescence enhancement caused by the formation of inclusion complexes and was performed at 290 and 360 nm for excitation and emission, respectively. The method involved a simple treatment of the samples with chloroform. Daunorubicin was used as internal standard. Limits of quantitation were 0.8 microM in plasma and 0.5 microM in cell lysate. Detection limits of 0.5 microM (50 pmol) and 0.3 microM (30 pmol) were obtained for MEBCD in the two media, respectively. Linear detection response was obtained for concentrations ranging from 1 to 100 microM in plasma and cell lysate. Recovery from plasma proved to be more than 40%. Precision, expressed as C.V. was in the range of 4 to 11%. Accuracy ranged from 89 to 105%.

Stereospecific determination of an HIV aspartyl protease inhibitor, PNU-103017, in rat, dog and human plasma using a Pirkle-concept high-performance liquid chromatographic column

A sensitive stereospecific high-performance liquid chromatographic assay for the quantitation of the enantiomers of 4-cyano-N-(3-(cyclopropyl-(5,6,7,8,9,10-hexahydro-4-hydroxy-2-oxo-2H- cycloocta(b)pyran-3-yl)methyl)phenyl)benzenesulfonamide (PNU-103017) (I), an HIV protease inhibitor, in plasma of rat, dog and human was developed. The procedure involved an acetonitrile-aided protein precipitation followed by solid-phase extraction (SPE) of I from plasma into ethanol. Stereospecific separation was accomplished on a Pirkle-concept chiral column (Regis S,S-Whelk-01, 250x4.6 mm I.D.) with a mobile phase of absolute ethanol-0.1% acetic acid in hexane (30:70, v/v). The eluate was monitored by UV absorbance (295 nm). Linear calibration curves were obtained in the range of 0.2 to 500 microM, with a lower limit of quantitation of 0.1-0.2 microM for both enantiomers in either rat, dog or human plasma. Intra- and inter-assay precision and assay accuracy were demonstrated to be acceptable for the stereoselective pharmacokinetic analysis of I in plasma.

Sensitive determination of docetaxel in human plasma by liquid-liquid extraction and reversed-phase high-performance liquid chromatography

A sensitive reversed-phase high-performance liquid chromatographic method has been developed and validated for the quantitative determination of docetaxel (I) in human plasma. The concentrations in plasma, for validation procedures spiked with known amounts of I, are read from calibration curves in the range of 10-20,000 ng/ml. The sample preparation involved a liquid-liquid extraction of 1000 microl of sample with a mixture of acetonitrile-n-butylchloride (1:4, v/v). The related compound paclitaxel (II) was used as internal standard. Chromatographic separations were performed an Inertsil ODS-80A column, with UV detection performed at 230 nm. The overall extraction recoveries were 84.3 and 90.0% for I and II, respectively. The lower limit of quantitation was 10 ng/ml, and the accuracy, within-run and between-run precisions at three tested concentrations fell within the generally accepted criteria for bioanalytical assays.

Direct determination of polyglucose metabolites in plasma using anion-exchange chromatography with pulsed amperometric detection

High-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) was evaluated for the quantitation of polyglucose metabolites (DP2-DP7) in human plasma. The method was investigated for accuracy, precision, specificity, linearity, range and analyte stability. Samples were prepared by dilution into the standard range (0.1-10 microg/ml) followed by deproteinization using a 30,000 molecular mass cut-off filtration device. The limit of detection was 0.05 microg/ml for all metabolites. Method precision for DP2-DP7 varied from approximately 2% R.S.D. in the upper range to approximately 15% R.S.D. at the limit of quantitation. Samples were stable following one or two freeze-thaw cycles and, after preparation, they could be refrigerated for up to 72 h. Application of this method to clinical plasma samples from continuous ambulatory peritoneal dialysis (CAPD) patients administered one daily night-time intraperitoneal exchange of 2 l of 7.5% polyglucose solution for four weeks indicated that plasma levels of DP2, DP3 and DP4 increased from baseline levels of <0.01 g/l to steady-state levels of 1.2+/-0.3, 1.2+/-0.3 and 0.4+/-0.1 g/l (mean+/-S.D.), respectively. These steady state plasma levels for DP2 and DP3 are comparable to previously reported levels in patients administered daily overnight 7.5% polyglucose dialysis solution.

A sensitive and selective method for the determination of mevalonic acid in dog plasma by gas chromatography/negative ion chemical ionization-mass spectrometry

A sensitive and selective method has been developed for the determination of mevalonic acid (MVA), a cholesterol biosynthetic precursor, in dog plasma using solid-phase extraction in combination with gas chromatography/negative ion chemical ionization-mass spectrometry (GC/NICI-MS). MVA extracted from plasma with a phenylboronic acid-bonded phase cartridge was converted to its pentafluorobenzyl (PFB) ester-cyclic boronate derivative to produce a carboxyltate anion [M-PFB]- in the NlCl mode. PFB ester boronate derivatives of MVA and its internal standard, d3-mevalonolactone, were monitored in the selected ion mode at m/z 213 and 216, respectively. The precision and accuracy of within-run and between-run assays were within 8%. This method was used to follow the diurnal variation of MVA levels in plasma of fasted and fed dogs. The diurnal variations of plasma MVA levels observed between the two groups were similar to those reported previously for human and rat plasma.

Simple and robust high-performance liquid chromatographic method for the determination of ranitidine in microvolumes of human serum

A simple robust high-performance liquid chromatographic method is described for the determination of ranitidine in microvolumes of human serum. The drug of interest was isolated using liquid-liquid extraction with dichloromethane and back-extraction with 0.1% phosphoric acid and separation was obtained using a reversed-phase column under isocratic conditions, with ultraviolet detection at 313 nm. Intra-day and inter-day coefficients of variation ranged from 1 to 6% and 3 to 10%, respectively. Accuracy of the assay was less than 10% at all concentrations. The limit of detection and the limit of quantitation were 2 and 7 ng/ml, respectively. The linearity was assessed in the range 10-1000 ng/ml. It was shown that a group of common drugs co-administered with ranitidine did not interfere with its determination. The applicability of this method for the pharmacokinetic study of ranitidine following i.v. infusion in patients was demonstrated using only 100 microl of serum. The ruggedness of the assay was demonstrated over a three-year period.

Determination of thiamphenicol in human plasma by micellar electrokinetic capillary chromatography

A micellar electrokinetic chromatographic method is described for the determination of thiamphenicol in human plasma. The plasma sample was basified by adding K2HPO4 and was then extracted with ethyl acetate. After the solvent was evaporated, the residue was reconstituted in water. Approximately 40 nl of the solution were injected hydrodynamically. The running buffer was 20 mM borate (pH 9.2) containing 40 mM sodium dodecyl sulfate and 10% acetonitrile. The applied voltage was 18 kV and the detector wavelength was set at 195 nm. On-column sample stacking was achieved during the analysis to enhance the sensitivity; the limit of quantitation was 0.1 microg/ml. Linearity was over the range of 0.2 to 10 microg/ml. Recovery was 93.7+/-3.3%, the intra-day precision and accuracy was 99.6+/-2.8%; the inter-day precision and accuracy was 98.4+/-3.4%. The concentration of thiamphenicol in human plasma from eight volunteers was measured after administering thiamphenicol capsules orally.

Determination of 5-fluorouracil and its main metabolites in plasma by high-performance liquid chromatography: application to a pharmacokinetic study

This paper describes a relatively simple and sensitive high-performance liquid chromatographic assay (HPLC) with ultraviolet absorbance detection for 5-fluorouracil (5-FUra) and its two main metabolites, 5-fluorouridine (5-FUrd) and 5-fluoro-2'-deoxyuridine (5-FdUrd), in plasma. In this study, two plasma clean-up procedures involving addition of internal standard, solid-phase and liquid-liquid extractions have been developed. A reversed-phase Kromasil C18 column was used. The detection was performed at 268 nm for 5-FUra and at 275 nm for the two metabolites. Linear detection responses were obtained for concentrations ranging from 25 to 1000 ng/ml. The average recovery from plasma was 35, 42 and 48% for 5-FUra, 5-FUrd and 5-FdUrd, respectively. Precision, expressed as C.V., ranged from 2.7 to 13% and the mean recovery from 94 to 105%. The limits of quantitation and detection of the three analytes were 20 and 10 ng/ml, respectively. The method was used to monitor the pharmacokinetic profile of 5-FUra and its two metabolites in patients with metastatic colorectal cancer.

Determination of LSD and N-demethyl-LSD in urine by liquid chromatography coupled to electrospray ionization mass spectrometry

A sensitive and highly specific method for the determination of LSD and N-demethyl-LSD in urine, using combined liquid chromatography and mass spectrometry (LC-MS) with electrospray ionization, has been developed. Extrelut-3 extraction cartridges were used for a basic sample clean-up. Elution was obtained by toluene-diethyl ether (60:40, v/v). A Nucleosil C18 (150 X 1 mm I.D.) reversed-phase column was used for the chromatographic separation, together with a mixture of 2 mM ammonium formate buffer (pH 3) and acetonitrile (70:30, v/v) as mobile phase. Recoveries were 93 and 80%, detection limits 0.025 and 0.035 ng/ml for LSD and N-demethyl-LSD, respectively. Intra-assay precision, studied at four concentrations, was better than 9% at the ng/ml range and better than 14% at 0.10 ng/ml for both compounds. Limits of quantitation were 0.05 and 0.10 ng/ml for LSD and N-demethyl-LSD, respectively. Reproducibility was good and linearity excellent for LSD in the range from 0.05 to 20 ng/ml (r>0.9999, n=7).

Determination of antisense phosphorothioate oligonucleotides and catabolites in biological fluids and tissue extracts using anion-exchange high-performance liquid chromatography and capillary gel electrophoresis

Chemically modified phosphorothioate oligodeoxynucleotides (ODNs) have become critical tools for research in the fields of gene expression and experimental therapeutics. Bioanalytical assays were developed that utilized fast anion-exchange high-performance liquid chromatography (HPLC) and capillary gel electrophoresis (CGE) for the determination of 20-mer ODNs in biological fluids (plasma and urine) and tissues. A 20 mer ODN in the antisense orientation directed against DNA methyltransferase (denoted as MT-AS) was studied as the model ODN. The anion-exchange HPLC method employed a short column packed with non-porous polymer support and a ternary gradient elution with 2 M lithium bromide containing 30% formamide. Analysis of the MT-AS is accomplished within 5 min with a detection limit of approximately 3 ng on-column at 267 nm. For plasma and urine, samples were diluted with Nonidet P-40 in 0.9% NaCl and directly injected onto the column, resulting in 100% recovery. For tissue homogenates, a protein kinase K digestion and phenol-chloroform extraction were used, with an average recovery of about 50%. Since the HPLC assay cannot provide one-base separation, biological samples were also processed by an anion-exchange solid-phase extraction and a CGE method to characterize MT-AS and its catabolites of 15-20-mer, species most relevant to biological activity. One base separation, under an electric field of 400 V/cm at room temperature, was achieved for a mixture of 15-20-mer with about 50 pg injected. Assay validation studies revealed that the combined HPLC-CGE methods are accurate, reproducible and specific for the determination of MT-AS and its catabolites in biological fluids and tissue homogenates, and can be used for the pharmacokinetic characterization of MT-AS.

Determination of a new antifungal agent, voriconazole, by multidimensional high-performance liquid chromatography with direct plasma injection onto a size-exclusion column

A fully automated method has been developed for the analysis of a new antifungal agent, voriconazole, in human plasma. Multidimensional chromatography was used with size-exclusion chromatography as the first step to separate plasma protein from the drug and internal standard which were then trapped on a precolumn of pellicular ODS. A reversed-phase column, Spherisorb ODS2, then separated drug and internal standard from one another and from remaining plasma components. With an injection of 0.56 ml plasma the limit of quantitation of the method was 5 ng/ml.

Tacrolimus (FK506): validation of a sensitive enzyme-linked immunosorbent assay kit for and application to a clinical pharmacokinetic study

Tacrolimus (FK506) is a macrolide immunosuppressant approved for the prophylaxis of organ rejection in liver transplant. Immunoassays of low intra- and interday variability and high sensitivity are necessary to adequately characterize terminal elimination phase concentrations in pharmacokinetic studies. A new ELISA kit for the quantitation of tacrolimus in human whole blood has been validated for use in pharmacokinetic studies. Methanol sample extracts were dried and reconstituted in a horseradish peroxidase (HPR)-FK506 conjugate solution. The reconstituted samples and mouse anti-FK506 were added to a microplate, precoated with secondary antibody, and incubated, FK506 and the HPR-FK506 conjugate competed to bind with anti-FK506, which was immobilized by binding to the secondary antibody. Unbound FK506 was washed away, and substrate was added for color development. Once the reaction was stopped with 2 N H2SO4, the plate was read at 450 nm. The linear range was 0.5-60 ng/ml, with a limit of quantitation of 0.5 ng/ml. Interday precision and accuracy were < or = 10.4% C.V. and < or = 3% R.E. for quality control samples. The lack of interference from endogenous compounds was established by parallelism and recoveries of FK506 from six lots of control matrix. Cross-reactivity against the metabolites and analogs were not performed because the kit monoclonal antibody was from the same source as Kobayashi et al (1). The utility and sensitivity of the kit present a good method for the quantitation of tacrolimus in blood from pharmacokinetic studies. The method is robust and has been used to assay tacrolimus in several thousand whole blood samples by multiple analysts.

Effect of variability of plasma interferences on the accuracy of drug immunoassays

Most immunoassays applied to drugs in human plasma do not use an extraction of analyte. To compensate for interferences due to plasma proteins or salts, standards are prepared in drug-free plasma. Because the concentration of plasma components varies from one subject to another, it is likely that the drug-free plasma is not representative of the potential interference in each plasma. Using two immunoassays, for a steroid (nomegestrol acetate) and a heptapeptide (BN 52080), the authors have shown that tracer binding to the antibody may vary significantly between plasma from different subjects. Intersubject variability of tracer-antibody binding was 21.6% (coefficient of variation for 25 subjects) for nomegestrol acetate. When the same plasma were spiked with the steroid at a concentration corresponding to the central part of the standard curve, the recovery was between 39 and 215%. Intersubject variability in tracer binding was lower (7.7%) for the peptide immunoassay, but still affected accuracy. The authors show that this problem is common to direct immunoassays for other drugs and must be solved in assay development.

Radioimmunoassay of zidovudine: extended use and potential application

When first approved, the dosing regimens for zidovudine were 1,200-1,500 mg/day; however, because toxicity developed, the daily dose had to be reduced to 500-600 mg/day. At these lower doses, plasma concentrations for a considerable segment of the dosing interval are often below the assay sensitivity for the high-performance liquid chromatography (HPLC) method. Although commonly used, the zidovudine radioimmunoassay has had minimal documentation for the quantitative analysis of clinical samples, especially at current doses. The authors' findings indicate that plasma, urine treated with phosphate buffer, and cerebrospinal fluid samples may be assayed using a commercially available radioimmunoassay. A good correlation was found for clinical samples measured by radioimmunoassay and HPLC (R2 = 0.85). The greater assay sensitivity, ability to process multiple specimens, and the relatively rapid turnaround time suggest that the zidovudine radioimmunoassay may have an important role in clinical trials evaluating zidovudine pharmacokinetics. This report summarizes the authors' experience with the zidovudine radioimmunoassay and focuses on its potential use in studying the role of therapeutic drug monitoring for zidovudine.

High-performance liquid chromatographic method for an automated determination of local anaesthetics in human plasma

A method is described that allows the rapid and precise determination of the local anaesthetics bupivacaine and etidocaine from biological fluids. This method uses a fully automated system with solid-phase extraction in combination with a column-switching technique. Both sample extraction on a LiChrocart pre-column and elution onto the analytical LiChrospher column, were performed automatically and concomitantly using conventional HPLC equipment in conjunction with an OSP-2 on-line sample preparator from Merck combined with UV detection. Recoveries were found to be 96.7 and 96.4% for 2 micrograms/ml bupivacaine and etidocaine, respectively. Lower limits of quantification were found to be 0.05 microgram/ml plasma for both of the compounds.

Determination of artemether and its metabolite, dihydroartemisinin, in plasma by high-performance liquid chromatography and electrochemical detection in the reductive mode

An analytical method for the determination of artemether (A) and its metabolite dihydroartemisinin (DHA) in human plasma has been developed and validated. The method is based on high-performance liquid chromatography (HPLC) and electrochemical detection in the reductive mode. A, DHA and artemisinin, the internal standard (I.S.), were extracted from plasma (1 ml) with 1-chlorobutane-isooctane (55:45, v/v). The solvent was transferred, evaporated to dryness under nitrogen and the residue dissolved in 600 microliters of water-ethyl alcohol (50:50, v/v). Chromatography was performed on a Nova-Pak CN, 4 microns analytical column (150 mm x 3.9 mm I.D.) at 35 degrees C. The mobile phase consisted of pH 5 acetate-acetonitrile (85:15, v/v) at a flow-rate of 1 ml/min. The analytes were detected by electrochemical detection in the reductive mode at a potential of -1.0 V. Intra-day accuracy and precision were assessed from the relative recoveries (found concentration in % of the nominal value) of spiked samples analysed on the same day (concentration range 10.9 to 202 ng/ml of A and 11.2 to 206 ng/ml of DHA in plasma). The mean recoveries over the entire concentration range were from 96 to 100% for A with C.V. from 6 to 13%, from 92% to 100% for DHA (alpha-tautomer) with C.V. from 4 to 16%. For A, the mean recovery was 96% at the limit of quantitation (LOQ) of 10.9 ng/ml with a C.V. of 13%. For DHA, the mean recovery was 100% at the LOQ of 11.2 ng/ml with a C.V. of 16%.

Determination of nalbuphine in human plasma by high-performance liquid chromatography with electrochemical detection. Application to a pharmacokinetic study

A high-performance liquid chromatographic procedure has been developed for the measurement of nalbuphine in plasma. Separation is performed on a reversed-phase analytical column (Ultrasphere ODS, 250 x 4.6 mm I.D., particle size, 5 microns). Mobile phase consisted of methanol-phosphate buffer (20:80, v/v) (pH 3.4). Electrochemical detection was performed using an ESA Coulochem II Model 5200 electrochemical detector equipped with a Model 5020 guard cell working at 550 mV and a Model 5021 analytical cell operating in the oxidation screening mode, with the potential of the first electrode set at 60 mV and the second electrode set at 450 mV. The method involves sample clean-up by liquid-liquid extraction using a chloroform-isopropanol mixture. After centrifugation, the organic phase was back-extracted with 17 mM phosphoric acid and then the aqueous phase was injected onto the column. The limits of quantitation and detection were 0.3 and 0.1 ng/ml, respectively. The extraction recovery was 91.1 +/- 3.7%. The intra- and inter-assay coefficients of variation were below 10%. Stability tests under various conditions have been performed. This method has been used to determine the pharmacokinetic parameters of nalbuphine in children.

High-performance liquid chromatographic determination of 9-(3-pyridylmethyl)-9-deazaguanine (BCX-34) in biological fluids

9-(3-Pyridylmethyl)-9-deazaguanine (BCX-34), a new purine nucleoside phosphorylase inhibitor, has selective immunosuppressive activity with potential therapeutic value in T-cell-mediated disease. We now report a sensitive, specific and reproducible method for measurement of 9-(3-pyridylmethyl)-9-deazaguanine in biological fluids using high-performance liquid chromatography (HPLC). 9-(3-Pyridylmethyl)-9-deazaguanine was extracted from plasma using perchloric acid precipitation followed by passage through Sep-Pak C18 cartridges (average extraction efficiency, 64.6%). Standard curves were linear over the range of interest (28-1120 ng/ml in plasma and 200-4000 ng/ml in urine, r2 > 0.999). Within-day and between-day coefficients of variation were less than 8%. The limit of quantitation was 28 ng/ml in plasma and 200 ng/ml in urine. This HPLC method should be useful in future clinical studies with this drug.

Determination of clozapine and its major metabolites in human plasma and red blood cells by high-performance liquid chromatography with ultraviolet absorbance detection

An isocratic high-performance liquid chromatographic (HPLC) method with UV absorbance detection is described for the quantification of clozapine (8-chloro-11-(4'-methyl)piperazino-5H-dibenzo[b,e]-1,4-diazepine) and its two major metabolites in plasma and red blood cells (RBCs). The method involves sample clean-up by liquid-liquid extraction with ethyl acetate. The organic phase was back-extracted with 0.1 M hydrochloric acid. Loxapine served as the internal standard. The analytes were separated by HPLC on a Kromasil Ultrabase C18 analytical column (5 microns particle size; 250 x 4.6 mm I.D.) using acetonitrile-phosphate buffer pH 7.0 (48:52, v/v) as eluent and were measured by UV absorbance detection at 254 nm. The limits of quantiation were 20 ng/ml for clozapine and N-desmethylclozapine and 30 ng/ml for clozapine N-oxide. Recovery from plasma or RBCs proved to be higher than 62%. Precision, expressed as % C.V., was in the range 0.6-15%. Accuracy ranged from 96 to 105%. The method's ability to quantify clozapine and two major metabolites simultaneously with precision, accuracy and sensitivity makes it useful in therapeutic drug monitoring.

Pharmacokinetics of intravenous and oral prethcamide in horses

The respiratory stimulant prethcamide is a mixture of equal parts of crotethamide and cropropamide. A specific and sensitive gas chromatographic method for the determination of crotethamide and cropropamide in horse plasma and urine is described. Both components of prethcamide were extracted from plasma and urine into dichloromethane. The extracts were analyzed by capillary gas chromatography with thermionic detection in the nitrogen-specific detection mode. The lower limits of quantitation were 4.0 ng ml-1 of plasma and 10.0 ng ml-1 of urine. Calibration curves were linear from 2.0-100 ng ml-1 of plasma for both components. Pharmacokinetic parameters for crotethamide and cropropamide after intravenous and oral dosing were estimated by analysis of plasma concentration versus time data. The total plasma clearance of cropropamide was greater than that of crotethamide and both values were greater than 5 ml min-1 kg-1. Renal clearance values of the two drugs were comparable and were much less than estimates of filtration clearance values in horses, indicating extensive re-absorption of both components from the renal tubules. Both compounds were metabolized by N-demethylation of the [(dimethylamino)-carbonyl]-propyl moiety and these metabolites were excreted in urine. The method was demonstrated to be suitable for detecting illicit administration of prethcamide to competition horses.

A rapid and specific assay for the determination of lamotrigine in human plasma by normal-phase HPLC

A rapid and specific high-performance liquid chromatography assay of lamotrigine in human plasma is described. Lamotrigine is extracted with dichloromethane from buffered plasma to which an internal standard has been added. The solvent is directly injected into a 250 x 4.6-mm Spherisorb Silica column and the drug is eluted by using a mixture of methanol, n-heptane, dichloromethane, and 28-30% ammonium hydroxide (20:40:40:0.3 vol/vol) at a flow rate of 1 ml/min. The eluates are detected at 240 nm. The assay requires 250 microliters of sample, and concentrations as low as 0.4 microgram/ml can be measured accurately. The method is linear in the range of 0.4-16 micrograms/ml, with a mean coefficient of correlation (r) > or = 0.997. Within- and between-day relative standard deviations at three different concentration levels (1, 4, and 8 micrograms/ml) are < or = 8.6%.

Determination of angiotensin II receptor antagonist (E4177) in human plasma and urine by high-performance liquid chromatography

A sensitive reversed-phase high-performance liquid chromatographic (HPLC) method with fluorescence detection was developed for the analysis of a new angiotensin II receptor antagonist, E4177, in human plasma and urine. The analyte and internal standard (I.S.) are extracted from acidified plasma and urine by liquid-liquid extraction and then refined by solid-phase extraction. The extraction recovery was greater than 90%. E4177 and I.S. were separated from endogenous components in plasma and urine on a C18 column using a mobile phase of acetonitrile-water-85% phosphoric acid (27.3:72.0:0.7, v/v). The eluent was monitored by fluorescence with excitation and emission set at 280 and 380 nm, respectively. The assay was linear from 2.5 to 1000 ng/ml of plasma and from 5 to 1500 ng/ml of urine. The limit of quantification was 2.5 and 5 ng/ml for plasma and urine, respectively. Inter- and intra-day coefficients of variation for the plasma and urine ranged from 0.6 to 4.7%. E4177 was stable in plasma and urine for at least 9 months during storage at -20 degrees C, respectively. The method was successfully applied to the determination of E4177 in plasma and urine for a pharmacokinetic study.

Microencapsulation of theophylline using ethylcellulose: in vitro drug release and kinetic modelling

This study details the process of coating theophylline with ethylcellulose using the coacervation technique of microencapsulation. Microencapsulation of theophylline not only renders it sustained-release, but also decreases its gastric irritation and masks the bitter taste (Lin and Yang 1987). The non-solvent addition method was chosen through a literature survey to ascertain various phases of the coacervate (Robinson 1989, Nixon and Wong 1990). A three-phase diagram was used to determine the optimum quantity of each component required. Steps were then carried out to optimize the production. Drug release rates of the prepared microcapsules were determined over 12-h cycles using the U.S.P. dissolution apparatus and the results obtained were compared with those of Knoll's (Germany) sustained-release theophylline capsules. Significant control over the rate of drug released from the developed dosage form was achieved during the experiment time (12 h). It is concluded that the method employed in this study could be effectively used in the preparation of sustained-release theophylline microcapsules capable of releasing their drug content for an extended period of time. Kinetic studies suggested that both the prepared microcapsules and Knoll's product followed Higuchi's model for drug release. Particle size and release data analysis from five consecutive batches prepared in the laboratory indicated suitable reproducibility of the coacervation process.

Enantioselective determination of FCE 28833, a new potential antiischemic agent, in gerbil plasma using column switching HPLC with UV detection

A sensitive and selective high performance liquid chromatographic method using an automated column switching technique for the determination of FCE 28833 enantiomers in gerbil plasma was developed. After solid-liquid extraction using a Supelcosil C18 cartridge, FCE 28833 was eluted on a clean-up column (Spherisorb CN) and the enantiomers were separated using an analytical chiral column (Crownpack CR(+)). The mobile phase (15% methanol in HClO4 1 mM) was directed through the columns at a flow rate of 1 ml/min and the fraction eluted between 13 and 40 min was transferred from the clean-up column into the analytical column. FCE 28833 enantiomers were monitored at 257 nm. The limit of quantitation of the method was 20 ng/ml plasma for both enantiomers and proved to be linear, precise, and accurate for the assay of both enantiomers in the 20-6,000 ng/ml concentration range. No interference from the blank gerbil plasma sample was observed. The suitability of the method was assessed using plasma samples obtained from male gerbils treated with a single oral dose (400 mg/kg) of FCE 28833.

An evaluation of the accuracy of four ELISA methods for measuring natural and recombinant human interferon-g

We describe an evaluation of four ELISA methods, including three commercial kits, for measuring recombinant and natural human interferon-g (hIFN-g). Using a panel of samples, including well-characterized reference standards, we compared relative quantification between assays, within assays and, where possible, the absolute accuracy of quantification as compared to other analytical methods. The four assays generated markedly different results; up to an almost 60-fold difference between the highest and lowest values for one sample. The differences between assays were not necessarily predictable. No single correction factor could be determined to correct results from one method to another across the panel of samples tested. We conclude that investigators should be diligent to revalidate commercial methods before depending on such methods and resultant data.

Validation of liquid chromatographic and gas chromatographic methods. Applications to pharmacokinetics

Validations of analytical methods are important for the generation of data for bioavailability, bioequivalence and pharmacokinetic studies. It is essential to use well defined and fully validated analytical methods to obtain reliable results that can be satisfactorily interpreted. This manuscript is intended to provide guiding principles for the evaluation of a method's overall performance. For this purpose, all of the variables of the method are considered, including sampling procedure, sample preparation, chromatographic separation, detection and data evaluation. The criteria considered are as follows: stability, selectivity, limits of quantification and of detection, accuracy, precision, linearity, recovery and ruggedness. Models used for analytical calibration curves are explained in term of validity and limitations, along with a presentation of the most common statistical considerations used to validate the model. Appropriate means of testing precision and accuracy, the most important factors in assessing method quality, are presented. Other issues, such as re-validation, cross-validation, partial sample volume, endogenous drugs and biological matrix of limited availability, are also discussed.

Comparison between gas chromatography-atomic emission detection and gas chromatography-mass spectrometry for the assay of propofol

Quantitation by gas chromatography-atomic emission detection (GC-AED) is based on the intensity of the signal measured at a wavelength characteristic of an element, after atomisation by the plasma. This response depends only on the number of atoms of this element present in the molecule under investigation, and is independent of the structure of the molecule. This technique was used for the assay of propofol, and the estimation of its two metabolites, after calibration with standard solutions of pure propofol. The results were compared with those obtained by gas chromatography-mass spectrometry (GC-MS). Propofol was quantified with higher precision and accuracy by GC-AED than by GC-MS which exhibited larger residual values. Concentration assessment for two metabolites showed a better agreement with the theoretical value by GC-AED since the response depends only on the number of carbon atoms in each molecule.

High-performance liquid chromatographic assay for melphalan in human plasma. Application to pharmacokinetic studies

This paper describes a simple, rapid and reproducible high-performance liquid chromatographic method (HPLC) with ultraviolet absorbance detection for the analysis of melphalan in plasma. The HPLC column was an Ultrasphere ODS (5 microns) and the eluent was composed of methanol, purified water and acetic acid (49.5:49.5:1, v/v). The detection was performed at 261 nm. The method involved a simple treatment of the samples with methanol. The propylparaben was used as internal standard. Linear detection response was obtained for concentrations ranging from 50 to 2500 ng/ml. Recovery from plasma proved to be more than 90%. Precision, expressed as C.V., was in the 0.5 to 9% range. Accuracy ranged from 95 to 102%. This method was used to determine the pharmacokinetic parameters of melphalan following high-dose (140 mg/m2) intravenous administration in patients with advanced malignancies undergoing peripheral blood hematopoietic progenitor-cell transplantation.

Analysis of clobazam and its active metabolite norclobazam in plasma and serum using HPLC/DAD

This report describes a simple reversed-phase high-performance liquid chromatographic (HPLC) method with automated solid-phase extraction (SPE) for analysing clobazam and norclobazam concentrations in human serum or plasma. For the HPLC analysis the samples and standards are prepared with an ASPEC automatic sample preparer using 100-mg Bond-Elut C-18 solid-phase extraction columns. The HPLC method is an isocratic method with a mobile phase of acetonitrile:methanol:10 mmol l-1 dipotassium hydrogen phosphate, pH 3.7 (30:2:100), at a flow rate of 1.5 ml min-1. The benzodiazepines are detected with a diode array detector (DAD) at 240 nm and the peak purity analyses are performed at 210-365 nm. The recovery is over 97% for both analytes, and it is independent of the drug concentration. The intra-assay CVs vary between 0.7 and 2.2% and inter-assay CVs between 3.8 and 4.6% at therapeutic drug concentrations. The detection limit is 15 nmol l-1. The assay is linear from 30 to 20,000 nmol l-1 (clobazam) and from 170 to 105,000 nmol l-1 (norclobazam). This method leads to a very good separation of norclobazam from carbamazepine and phenytoin. None of the anti-epileptic or antidepressant drugs tested interfere with the assay.

The impact of column temperature in the high performance liquid chromatographic analysis of topotecan in rat and dog plasma

A sensitive high performance liquid chromatographic (HPLC) assay has been developed and validated for the quantitation of the novel anticancer agent topotecan and topotecan as its lactone plus carboxylate forms in rat and dog plasma. Linear responses in analyte standard peak areas were observed over the concentration ranges 0.10-10 ng ml-1 using 100 microliters of rat plasma and 0.2-100 ng ml-1 using 100 microliters of dog plasma. Due to the instability of the drug in the biological matrix it was necessary to obtain the plasma fraction within 5 min after blood sampling by centrifugation, immediately followed by protein precipitation with cold methanol (-30 degrees C). For the determination of total drug levels (lactone plus lactone ring-opened form), plasma samples were deproteinated with methanol and subsequently acidified with 2% (v/v) perchloric acid. The samples were analysed by HPLC using a Zorbax SB-C18 Stable Bond column and methanol-0.1 M hexane-1-sulfonic acid in methanol-0.01 M N,N,N'N'-tetramethylethylenediamine in distilled water pH 6.0 (25:10:65, v/v/v) as the mobile phase. The detection was performed fluorimetrically. The analytical column was thermostated at 19-21 degrees C to obtain baseline resolution between an interfering endogenous compound in rat and dog plasma and topotecan. This endogenous peak was absent in human plasma. Variation of chromatography temperature appeared to be a very useful tool in the bioanalysis of topotecan. It allowed optimization of the separation between the endogenous compound and the analyte; different mechanisms of solute interactions are apparently involved in this reversed-phase ion-pair chromatographic system.

Quantitative determination of norethisterone acetate in human plasma by capillary gas chromatography with mass-selective detection

An analytical method for the determination of norethisterone acetate (NETA) in human plasma by capillary gas chromatography-mass-selective detection (GC-MS), with testosterone acetate as internal standard, was developed and validated. After addition of the internal standard, the compounds were extracted from plasma at basic pH into diethyl ether-dichloromethane (3:2, v/v), which was then evaporated to dryness. The compounds were converted into their pentafluoropropionyl derivatives which were determined by gas chromatography using a mass selective detector at m/z 486 for NETA and m/z 476 for the internal standard. Intra-day and inter-day accuracy and precision were found suitable over the range of concentrations between 0.10 to 10 ng/ml. The method was applied to clinical samples.

Determination of trace lithium in biological fluids using graphite furnace atomic absorption spectrophotometry: variability of urine matrices circumvented by cation exchange solid phase extraction

A graphite furnace atomic absorption spectrometry method has been developed for the quantitative determination of submicromolar endogenous concentration of lithium in human plasma and urine using pyrolitically-coated graphite tubes in combination with ammonium nitrate matrix modification. This latter treatment could not completely abolish the interferences caused by the matrix, notably in urine samples. The variability of the urinary matrices required an additional standardization procedure by solid-phase extraction on strongly acidic cation exchange cartridges. Matrix-matched samples were used for the establishment of calibration curves with the addition-calibration method. Calibration curves were linear up to 0.72 mumol/l (1.0 > r2 > 0.99). The described method enables accurate measurements of trace-lithium in biological samples at concentrations down to 0.03 mumol/l with intra- and inter-day variabilities < 10%. The method was applied to the determination of trace-lithium levels in urine and plasma samples from healthy individuals enabling the calculation of its fractional excretion (FeLi) (median range 17.3%), a value which reflects the functional capacity of the kidney to reabsorb sodium and water at the proximal tubular portion of the nephron. This sensitive method can thus be used as an investigative and diagnostic tool in various renal pathophysiological conditions, in clinical research, and may also be applied to studies on the trace-lithium status of population in connection with psycho-affective disorders.