Simultaneous determination of phenylbutazone and its metabolites in plasma and urine by high-performance liquid chromatography

A high-performance liquid chromatographic method was developed for the simultaneous determination of phenylbutazone and its metabolites, oxyphenbutazone and γ-hydroxyphenylbutazone, in plasma and urine. Samples were acidified with hydrochloric acid and extracted with benzene—cyclohexane (1:1, v/v). The extract was redissolved in methanol and chromatographed on a μBondapak C₁₅ column using a mobile phase of methanol—0.01 M sodium acetate buffer (pH 4.0) in a linear gradient (50 to 100% methanol at 5%/min; flow-rate 2.0 ml/min) in a high-performance liquid chromatograph equipped with an ultra-violet absorbance detector (254 nm). The detection limit for phenylbutazone, oxyphenbutazone and for γ-hydroxyphenylbutazone was 0.05 μg/ml.A precise and sensitive assay for the determination of phenylbutazone and its metabolites was established.     

Simultaneous analysis of disopyramide and quinidine in plasma by high-performance liquid chromatography

A new reversed-phase high-performance liquid chromatographic method allowing simultaneous measurement of plasma concentrations of disopyramide and quinidine is described. Disopyramide and quinidine were separated on a reversed-phase column using 0.05 M phosphate buffer (pH 3.0)—acetonitrile (73:27, v/v), as mobile phase and the peaks were monitored by UV absorbance at the wavelengths of 254 and 325 nm. The drugs were extracted from alkaline plasma with chloroform containing the internal standard. The organic phase was evaporated to dryness and the residue was redissolved in a small volume of the mobile phase before analysis by high-performance liquid chromatography. The method is convenient and reliable in routine monitoring of both drugs.     

High-performance liquid chromatographic method for the direct determination of 4-methylumbelliferone and its glucuronide and sulfate conjugates: Application to studies in the single-pass in situ perfused rat intestine—liver preparation

A direct high-performance liquid chromatographic (HPLC) assay was developed for the separation and determination of 4-methylumbelliferone (4MU) and its glucuronide (MUG) and sulfate (MUS) conjugates in the cell-free perfusate (“plasma”) from in situ perfused rat intestine—liver preparation. In addition, a procedure was developed to extract and determine 4MU in the whole blood perfusate. Perfusate plasma containing an internal standard (umbelliferone) was precipitated with methanol (1:4, v/v), and injected into a reversed-phase HPLC system with gradient elution. 4MU and the same internal standard were also extracted directly from the whole blood perfusate with ethyl acetate and injected into a reversed-phase HPLC system with isocratic elution. Inter- and intra-day precision studies (n = 5 for each) for both the plasma and whole blood procedures demonstrated relative standard deviations of less than 10% at all concentrations studied. The compounds were stable in either the plasma or blood extracts at room temperature for up to 72 h. The procedures were successfully used to analyze perfusate samples obtained from the single-pass in situ perfusion of rat intestine—liver system with either trace (0.95 nM) or 32.3 μM concentrations of 4MU. The intestine was responsible for the formation of most of the MUG formed by the intestine—liver preparation during steady-state perfusion with either input concentration of 4MU.     

High-performance liquid chromatographic determination of pipotiazine in human plasma and urine

A high-performance liquid chromatographic method has been developed for the determination of pipotiazine in human plasma and urine. After selective extraction, pipotiazine and the internal standard (7-methoxypipotiazine) are chromatographed on a column packed with Spherosil XOA 600 (5 μm) using a 7:3 (v/v) mixture of diisopropyl ether—isooctane (1:1, v/v) + 0.2% triethylamine and diisopropyl ether—methanol (1:1, v/v) + 0.2% triethylamine + 2.6% water. The eluted compounds are measured by fluorescence detection. The sensitivity of the method was established at 0.25 ng/ml pipotiazine in plasma and 2 ng/ml pipotiazine in urine (C.V. < 5%). The method has been successfully applied to a pharmacokinetic study following a single oral administration of 10 mg of pipotiazine.     

Determination of ibuprofen in serum by high-performance liquid chromatography and application to ibuprofen disposition

A high-performance liquid chromatographic method for quantitation of ibuprofen from serum and application of this method to ibuprofen disposition in the dog is described. The drug was extracted from acidified plasma with dichloromethane. The internal standard used was a methanolic solution of 4-n-butylphenylacetic acid. A μBondapak C₁ column was used for analysis; the mobile phase was methanol—water—glacial acetic acid (pH 3.4) (75:24:1, v/v). A wavelength of 272 nm was used to monitor ibuprofen and the internal standard.Method sensitivity was 0.5 μg/ml serum using either 0.5 or 1.0 ml of sample, and no interference was found from endogenous compounds or other commonly used anti-inflammatory agents. The coefficients of variation of the method were 4.2% and 6.0% for samples containing 50.0 and 6.25 μg/ml of ibuprofen, respectively, and the calibration curve was linear for the range of 0.5 to 100 μg/ml. This method was demonstrated to be suitable for pharmacokinetic and/or biopharmaceutical studies of ibuprofen in man and the dog.     

Determination of acetylmethadol and metabolites by use of high-performance liquid chromatography

A method is described for the simultaneous determination of l,α-acetylmethadol (LAAM) and five active metabolites — noracetylmethadol, dinoracetylmethadol, methadol, normethadol, and dinormethadol — in biofluids by high-performance liquid chromatography using a normal-phase column and a UV detector at 218 nm. The compounds are recovered from biofluids by a multistep liquid—liquid extraction. The mobile phase is methanol—acetonitrile (70:30, v/v) containing 0.015% ammonium hydroxide as the modifier. Retention times can be varied by adjusting the composition of the mobile phase to maximize peak height for quantitation using l-propranolol as the internal standard or peak separation for the collection of fractions. Using a UV detector the lower limit of sensitivity is 10 ng/ml of biofluid. Using fraction collection of radiolabeled drug and metabolites followed by liquid scintillation counting the lower limit of sensitivity is 1.0 ng/ml. Commonly used or abused narcotics including morphine, heroin, meperidine, methadone and propoxyphene do not interfere with the analysis. The method has been applied to plasma and urine samples from humans, sheep and rats. Extracts of urine from patients receiving maintenance treatment with LAAM contain LAAM and each of the five active metabolites.     

Stereoselective and simultaneous measurement of cis- and trans-isomers of doxepin and N-desmethyldoxepin in plasma or urine by high-performance liquid chromatography

Doxepin is a tricyclic antidepressant marketed as an irrational mixture of cis- and trans-geometric isomers in the ratio of 15:85. A convenient high-performance liquid chromatographic (HPLC) procedure for simultaneous quantitation of geometric isomers of doxepin and N-desmethyldoxepin in plasma and urine is described. The HPLC procedure employed a normal phase system with a silica column and a mobile phase consisting of hexane-methanol-nonylamine (95:5:0.3, v/v/v), a UV detector and nortriptyline as the internal standard. The liquid-liquid extraction solvent was a mixture of n-pentane-isopropanol (95:5, v/v). The limit of quantitation was 1 ng/ml for each isomer. The calibration curves were linear over the ranges 1–200 ng/ml (plasma) and 1–400 ng/ml (urine). In plasma, the accuracy (mean±S.D.) (97.53±1.67%) and precision (3.89±1.65%) data for trans-doxepin were similar to corresponding values for urine, i.e., 97.10±2.40 and 3.82±1.14%. Accuracy and precision data for trans-N-desmethyldoxepin in plasma were 97.57±2.06 and 4.38±3.24%, and in urine were 97.64±3.32 and 5.26±1.83%, respectively. Stability tests under three different conditions of storage indicated no evidence of degradation. The recovery of doxepin was 61–64% from plasma and 63–68% from urine. The method has been applied to analyses of plasma and urine samples from human volunteers and animals dosed with doxepin.     

Stereoselective determination of R(−)- and S(+)-MK-571, a leukotriene D4 antagonist,in human plasma by chiral high-performance liquid chromatography

A stereoselective high-performance liquid chromatographic method that utilizes fluorescence detection was developed for the selective and sensitive quantification of R(−)- and S(+)-enantiomers of MK-571 (1), a potent and specific leukotriene D₄ antagonist, in human plasma. Racemic 1 was isolated from the acidified plasma using solid-phase extraction and the resulting residue was successfully reacted with isobutyl chloroformate and R(+)-1-(1-naphthyl)ethylamine in triethylamine—acetonitrile medium to form the diastereomer of each enantiomer. A structural analogue of 1 was used as internal standard. The derivatized sample was dissolved in 1,1,2-trichlorotrifluoroethane and an aliquot was chromatographed on a (R)-urea chiral column using a mobile phase containing 89% triethylamine—pentane (3:1000, v/v), 10% 2-propanol, and 1% acetonitrile at a flow-rate of 1.5 ml/min. The fluorescence response (excitation wavelength, 350 nm; emission wavelength, 410 nm) was linear (r²>0.999) for concentrations of enantiomers of 1 from 0.05 μg/ml, the lowest quantitation limit, up to 2.5 μg/ml. Intra-day coefficients of variation at 0.05 μg/ml were 2.4% for the R(−)-isomer and 2.0% for S(+)-isomer. The corresponding inter-day coefficients of variation for R(−)- and S(+)-1 were 2.6 and 3.6%, respectively. The utilit of the methodology was established by analysis of plasma samples from male volunteers receiving single intravenous and oral doses of racemic 1.     

Measurement of bumetanide in plasma and urine by high-performance liquid chromatography and application to bumetanide disposition

A high-performance liquid chromatographic method for the measurement of bumetamide in plasma and urine is described. Following precipitation of proteins with acetonitrile, bumetanide was extracted from plasma or urine on a 1-ml bonded-phase C₁₈ column and eluted with acetonitrile. Piretanide dissolved in methanol was used as the internal standard. A C₁₈ Radial Pak column and fluorescence detection (excitation wavelength 228 nm; emission wavelength 418 nm) were used. The mobile phase consisted of methanol—water—glacial acetic acid (66:34:1, v/v) delivered isocratically at a flow-rate of 1.2 ml/min. The lower limit of detection for this method was 5 ng/ml using 0.2 ml of plasma or urine. Nafcillin, but not other semi-synthetic penicillins, was the only commonly used drug that interfered with this assay. No interference from endogenous compounds was detected. For plasma, the inter-assay coefficients of variation of the method were 7.6 and 4.4% for samples containing 10 and 250 ng/ml bumetanide, respectively. The inter-assay coefficients of variation for urine samples containing 10 and 2000 ng/ml were 8.1 and 5.7%, respectively. The calibration curve was linear over the range 5–2000 ng/ml.     

Determination of metyrapone and the enantiomers of its chiral metabolite metyrapol in human plasma and urine using coupled achiral-chiral liquid chromatography

A coupled achiral-chiral liquid chromatographic assay has been developed to determine the concentrations of metyrapone and the enantiomers of its chiral metabolite metyrapol in plasma and urine. The chromatographic system consisted of a silica precolumn (75 × 4.6 mm I.D.) coupled in-line to a 250 × 4.6 mm I.D. column containing cellulose tris(4-methylbenzoate) coated on silica gel (Chiralcel OJ-CSP). When plasma samples were analyzed, the mobile phase was hexane-ethanol (92:8, v/v) modified with 0.1% diethylamine and when urine samples were analyzed the mobile phase was hexane-ethanol (94:6, v/v) modified with 0.2% diethylamine. Under these chromatographic conditions the chromatographic retentions [expressed as capacity factors (k′)] for metyrapone were k′ = 2.35 (plasma) and 2.52 (urine); for (−)-metyrapol k′ = 4.22 (plasma) and 4.62 (urine); for (+)-metyrapone k′ = 5.16 (plasma) and 5.86 (urine); enantioselectivities (α) were 1.09 (plasma) and 1.13 (urine). The assay has been validated for use in metabolic studies. The analyses of plasma and urine samples from one subject following oral administration of 750 mg of metyrapone indicated that the enzymatic reduction of myterapone by aldo-keto reductase was enantiospecific.     

Stereospecific determination of tiaprofenic acid in plasma: problems with drug degradation

A sensitive stereospecific high-performance liquid chromatographic assay for the quantification of tiaprofenic acid in human plasma was developed. The procedure involved extraction of tiaprofenic acid from acidified plasma into hexane-diethyl ether (8:2, v/v). Stereospecific separation was achieved with a prepacked ga₁-acid glycoprotein column without derivatization. The mobile phase consisted of 2% 2-propanol in 0.01 M phosphate buffer, pH 6.5. Tiaprofenic acid was detected at 317 nm. The limit of quantification was found to be 25 ng/ml for each enantiomer using a 0.5 ml plasma sample. The assay was reproducible and accurate to be applied to the stereoselective pharmacokinetic analysis of tiaprofenic acid in plasma. Because of photoinstability of tiaprofenic acid plasma sampling and sample extraction should be performed under light protection.     

Isocratic reversed-phase liquid chromatographic of all-trans-retinoic acid and its major metabolites in new potential supplementary test systems for developmental toxicology

An isocratic reversed-phase high-performance liquid chromatographic procedure for the determination of all-trans-retinoic acid (all-trans-RA) and its metabolites, all-trans-4-oxo-RA, 5,6-epoxy-RA, 9-cis-RA and13-cis-RA, in mouse plasma and embryo and in new in vitro potential test systems for development toxicology has been developed. These compounds, their biological precursor retinol (vitamin A) and the internal standard were resolved on a Spherisorb ODS-2 (5 μm) column (250×4.6 mm I.D.) with acetonitrile-water-methanol-n-butyl alcohol (56:37:4:3, v/v) containing 100 mM ammonium acetate and 70 mM acetic acid as the elution system with a total run time of 23 min. The assay was linear over a wide range, with a lower limit of quantitation of 50 ng/ml or 10 ng/ml of protein for all-trans-RA, 13-cis-RA and 9-cis-RA and of 25 ng/ml or 5 ng/ml protein for the 4-oxo- and 5,6-epoxy-metabolites. At these concentrations, intra-assay coefficients of variation (C.V.) of the retinoids were 3–9%. Mean intra-assay C.V. averaged 5–7% in the tissues studied. Its use is discussed for RA measurements in some of the new test systems — Drosophila melanogaster, sea urchin embryos and cultured human keratinocytes — that have to be evaluated in toxicological testing, supplementary to standard assays in mammals.     

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 μl of water-ethyl alcohol (50:50, v/v). Chromatography was performed on a Nova-Pak CN, 4 μm analytical column (150 mm×3.9 mm I.D.) at 35°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 (α-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 CV of 13%. For DHA, the mean recovery was 100% at the LOQ of 11.2 ng/ml with a CV of 16%.     

Determination of cycloserine in human plasma by high-performance liquid chromatography with fluorescence detection,using derivatization with p-benzoquinone

A new method for determining cycloserine in plasma samples is described. This method is based on the derivatization of cycloserine with p-benzoquinone, a reaction that takes place at the same time as the process of plasma deproteinization due to the presence of ethanol as solvent in the solution of the derivatization reagent. Four derivatives are obtained from this reaction. The main derivative is well correlated with the cycloserine concentration. The ratio between the volumes of the plasma sample and the reagent solution is 1:2 for a p-benzoquinone concentration of 1000 μg/mL. Elution from a C₁₈ column was isocratic, using a mobile phase containing (v/v) 85% aqueous 0.1% formic acid solution, and 15% (v/v) of a mixture of methanol and acetonitrile (1:1), with a flow-rate of 1 mL/min, at 25°C. Determinations by fluorescence detection were achieved with excitation at 381 nm and emission at 450 nm, with a detection limit of 10 ng/mL for an injection volume of 5 μL. This method was validated and applied to the determination of cycloserine in blood plasma samples of several healthy volunteers.     

Determination of ticlopidine in human plasma by high-performance liquid chromatography and ultraviolet absorbance detection

A simple HPLC method has been developed for the determination of ticlopidine in human plasma. Plasma samples were buffered at pH 9 and extracted with n-heptane-isoamyl alcohol (98.5: 1.5, v/v). Imipramine was used as internal standard. Chromatography was performed isocratically with acetonitrile-methanol-0.05 M KH₂PO₄ (20:25:55, v/v) at pH 3.0 containing 3% triethylamine at a flow-rate of 1 ml/min. A reversed-phase column, Supelcosil LC-8-DB, 15 cm × 4.6 mm I.D., 5 μm particle size, was used. The effluent was monitored by UV absorbance detection at 235 nm. The method showed good accuracy, precision and linearity in the concentration range 5–1200 ng/ml. The limit of quantitation was 5 ng/ml, with a precision (C.V.) of 8.91%, which is the same as that achieved by other authors with a previously published GC-MS method. The procedure described in this paper is simple and allows the routine assessment of ticlopidine plasma concentration in pharmacokinetic studies following therapeutic doses in human subjects.     

Determination of omeprazole in human plasma by high-performance liquid chromatography

A new method for the determination of omeprazole in human plasma was developed. Omeprazole was extracted from plasma with toluene-isoamylalcohol (95:5, v/v), the organic phase was evaporated, dissolved in the mobile phase and injected into a reversed-phase C₁₈ column. Flunitrazepam was used as an internal standard. The mobile phase consisted of 47% methanol and 53% of 0.1 M dipotassium hydrogenphosphate, pH 7.8. The spectrophotometric detection was performed at 302 nm. Limit of quantitation was 9.7 ng/ml and the calibration curve was linear up to 1240 ng/ml.     

Stereoselective high-performance liquid chromatography determination of propranolol and 4-hydroxypropranolol in human plasma after pre-column derivatization

A stereoselective reversed-phase HPLC assay to quantify S-(−) and R-(+) enantiomers of propranolol and 4-hydroxypropranolol in human plasma was developed. The method involved liquid–liquid extraction for sample clean-up and employed 2,3,4,6-tetra-O-acetyl-β-glucopyranosyl isothiocyanate as a pre-column chiral derivatization reagent. The internal standard used was 4-methylpropranolol. The derivatized products were separated on an Altex C₁₈ column using a mixture of acetonitrile–water–phosphoric acid–triethylamine (58:42:0.1:0.06 and 50:50:0.15:0.06, v/v, for propranolol and 4-hydroxypropranolol, respectively) as mobile phase. The detection of propranolol derivatives was made at λ_ex=280 nm and λ_em=325 nm, and the corresponding 325 and 400 nm were used for 4-hydroxypropranolol derivatives. The assay was linear from 1 to 100 ng/ml and from 2 to 50 ng/ml using 0.5 ml of human plasma for propranolol and 4-hydroxypropranolol enantiomers, respectively. The present assay is used to quantify the enantiomers of propranolol and 4-hydroxypropranolol, respectively, in human plasma for pharmacokinetic studies.     

Differential pulse amperometric detection of drugs in plasma using a dropping mercury electrode as a high-performance liquid chromatographic detector

High-performance liquid chromatographic separation prior to reductive electrochemical determination at the dropping mercury electrode imparts specificity and sensitivity not attainable by conventional polarographic analysis of drugs and their metabolites. The utility of this novel approach is demonstrated by the analysis of chlordiazepoxide and its N-desmethyl metabolite in plasma which previously required thin-layer chromatographic separation prior to polarographic measurement. A mobile phase of methanol—isopropanol—0.0075 M acetate buffer, pH 3.5 (53:5:42), is used with the detector operated in the differential pulse mode at E_p = ?0.820 V vs. Ag/AgCl. The response was linear (r = 0.998) in the concentration range of 0.05–2.0 μg/ml plasma for each component. The minimum detectability for each component under these conditions is 5.0 ng injected at a current range of 0.5 μA full scale. Techniques for oxygen removal and hydrodynamic considerations for the pumping system are presented.     

Quantification of paclitaxel metabolites in human plasma by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic (HPLC) method has been validated for the quantitative determination of the three major paclitaxel metabolites (6α-hydroxypaclitaxel, 3′-p-hydroxypaclitaxel, 6α,3′-p-dihydroxypaclitaxel) in human plasma. The HPLC system consists of an APEX-octyl analytical column and acetonitrile-methanol-0.02 M ammonium acetate buffer pH 5 (AMW; 4:1:5, v/v/v) as the mobile phase. Detection is performed by UV absorbance measurement at 227 nm. The sample pretreatment of the plasma samples involves solid-phase extraction (SPE) on Cyano Bond Elut columns.The concentrations of the metabolic products could be determined by using the paclitaxel standard curve with a correction factor of 1.14 for 6α,3′-p-dihydroxypaxlitaxel. The recoveries of paclitaxel and the metabolites 6α,3′-p-dihydroxypaclitaxel, 3′-p-hydroxypaclitaxel and 6α-hydroxypaclitaxel in human plasma were 89, 78, 91 and 89%, respectively. The accuracy of the assay for the determination of paclitaxel and its metabolites varied between 95 and 97%, at a 50 ng/ml analyte concentration. The lower limit of quantitation was 10 ng/ml for both the parent drug and its metabolites.     

Determination of ticarcillin epimers in plasma and urine with high-performance liquid chromatography

A high-performance liquid chromatogaphic method was developed for determining the concentrations of ticarcillin (TIPC) epimers in human plasma and urine. Samples were prepared for HPLC analysis with a solid-phase extraction method and the concentrations of TIPC epimers were determined using reversed-phase HPLC. The mobile phase was a mixture of 0.005 M phosphate buffer (pH 7.0) and methanol (12:1, v/v) with a flow-rate of 1.0 ml/min. TIPC epimers were detected at 254 nm. Baseline separation of the two epimers was observed for both plasma and urine samples with a detection limit of ca. 1 μg/ml with a S/N ratio of 3. No peaks interfering with either of the TIPC epimers were observed on the HPLC chromatograms for blank plasma and urine. The recovery was more than 80% for both plasma and urine samples. C.V. values for intra- and inter-day variabilities were 0.9–2.1 and 1.1–6.4%, respectively, at concentrations ranging between 5 and 200 μg/ml. The present method was used to determine the concentrations of TIPC epimers in plasma and urine following intravenous injection of TIPC to a human volunteer. It was found that both epimers were actively secreted into urine and that the secretion of TIPC was not stereoselective. Plasma protein binding was also measured, which revealed stereoselective binding of TIPC in human plasma.