LC determination of praziquantel in human plasma

A simple high-performance liquid chromatographic (HPLC) method for the determination of praziquantel in human plasma was developed and validated. The present method was described by adding drop-wise 0.2 M Zinc sulfate and acetonitrile to plasma sample for deproteinization. This method used a reversed-phase Spherisorb ODS 2 column (5 microm), 250 x 4.6 mm i.d. as a stationary phase with a mobile phase consisting of acetonitrile- methanol-water (36:10:54, v/v/v), a flow rate of 1.5 ml/min and UV detection wavelength of 217 nm. Diazepam was used as internal standard. The standard calibration curve was linear over the concentration range of 100-2000 ng/ml (r=0.999). The equation of a linear regression line was y=8.05E-04+7.25E-04x with slope and intercept values of 0.0007 and 0.0008, respectively. The limit of detection was 12.25 ng/ml and the limit of quantification was set at 100 ng/ml. The intra- and inter-day assay coefficients of variation (CV) were 3.0+/-1.7 and 6.3+/-1.9%, respectively. The percentage of recovery was 102.1+/-5.6. Therefore, the HPLC method described here was simple, rapid and reproducible since it did not require extraction and evaporation processes in sample preparation, which will reduce time-consuming or expensive sample preparation.     

A sensitive method for determination of COL-3, a chemically modified tetracycline, in human plasma using high-performance liquid chromatography and ultraviolet detection

COL-3, 6-deoxy-6-desmethyl-4-desdimethylamino-tetracycline, is a matrix metalloproteinase inhibitor currently in clinical development. A HPLC-UV method to quantitate COL-3 in human plasma was developed. COL-3 was extracted from plasma using solid-phase extraction cartridges. COL-3 is separated on a Waters Symmetry Shield RP8 (3.9 mm x150 mm, 5 microm) column with EDTA (0.001 M) in sodium acetate (0.01 M, pH 3.5)-acetonitrile mobile phase using a gradient profile at a flow rate of 1 ml/min for 22 min. Carryover was eliminated by using an extended needle wash of methanol:acetonitrile:dichloromethane (1:1:1, v/v/v). Detection of COL-3 and the internal standard, chrysin, was observed at 350 nm. COL-3 and chrysin elute at 8.9 and 9.9 min, respectively. The lower limit of quantitation in human plasma of COL-3 was 75 ng/ml, linearity was observed from 75 to 10,000 ng/ml. A 30,000 ng/ml sample that was diluted 1:50 with plasma was accurately quantitated. This method is rapid, widely applicable, and suitable for quantifying COL-3 in patient samples enabling further clinical pharmacology characterization of COL-3.     

Determination of colchicine in mouse plasma by high performance liquid-chromatographic method with UV detection and its application to pharmacokinetic studies

A simple and sensitive high performance liquid chromatography method with UV detection was described for the determination of colchicine (COL) in mouse plasma. After single-step deproteinization by acetonitrile using berberine hydrochloride as an internal standard (I.S.), solutes were separated on a Diamonsil C(18) column (250 mm x 4.6 mm I.D., 5 microm particle size) (Dikma), using acetonitrile-0.15% phosphoric acid solution (27:73, v/v) as mobile phase (flow-rate 1.0 ml/min); wavelength of the UV detector was set at 350 nm. No interference from any endogenous substances was observed during the elution of COL and internal standard (I.S., berberine hydrochloride). The retention times for COL and I.S. were 11.23 min and 8.82 min, respectively. The limit of quantification was evaluated to be 1.5 ng/ ml and the limit of detection was 0.5 ng/ml. The method was used in the study of pharmacokinetics of COL after intravenous injection (i.v.) and intraperitoneal injection (i.p.). The result indicated that COL disappears from the plasma according to a three compartment open model.     

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

A high performance liquid chromatographic method for the quantitation of celecoxib (CEL) in human plasma is presented. The method is based on liquid-liquid extraction with chloroform and reversed-phase chromatography using a Nucleosil CN column (250 mm x 4.6 mm i.d., 5 microm particle size) and UV spectrophotometer detection at 260 nm. The mobile phase consists of acetonitrile:water (60:40 (v/v)). Flutamide was used as internal standard (IS). The assay was linear in the concentration range of 10-1000 ng/ml when 0.5 ml aliquots of plasma were extracted. Within-day and between-day precision expressed by relative standard deviation is less than 4% and inaccuracy does not exceed 3%. The assay was used to analyze samples collected during human clinical studies.     

Determination of endothelin antagonist BMS182874 in plasma by high-performance liquid chromatography

A simple and rapid high performance liquid chromatography (HPLC) method was developed for the determination of BMS182874 (BMS) in mouse plasma. The drug was extracted from plasma by a liquid-liquid extraction process. The method consists of reversed-phase chromatography using a Thermo Hypersil-Keystone RP-18 5 microm, 250 x 2.1 mm column and UV spectrophotometer detection at 255 nm. The mobile phase consists of 45% (v/v) acetonitrile: 55% (v/v) trifluoroacetic acid (0.015% v/v; pH 3.0) at a flow rate of 0.6 ml/min. Validity of the method was studied and the method was precise and accurate with a linearity range from 100 ng/ml to 1000 ng/ml. The extraction efficiency was found to be 81, 84 and 87% for 100, 500 and 1000 ng/ml, respectively for spiked drug in plasma. The limit of quantification and limit of detection were found to be 50 and 10 ng/ml, respectively in plasma. Within-day and between-day precision expressed by relative standard deviation was less than 4% and inaccuracy did not exceed 4%. The assay was also used to analyze samples collected during animal studies. The suitability and robustness of the method for in vivo samples were confirmed by analysis of BMS from mouse plasma and tissues dosed with BMS.     

High-performance liquid chromatography method for determining alendronate sodium in human plasma by detecting fluorescence: application to a pharmacokinetic study in humans

A high-performance liquid chromatographic (HPLC) method was developed using diethylamine (DEA) solid-phase extraction (SPE), 9-fluorenylmethyl derivative (FMOC) and fluorescence detection for quantifying alendronate in human plasma. Sample preparation involved a manual protein precipitation with trichloroacetic acid, a manual coprecipitation of the bisphosphonate with calcium phosphate and derivatization with 9-fluorenylmethyl chloroformate in citrate buffer at pH 11.9. Liquid chromatography was performed on a Capcell Pak C(18) column (4.6 mm x 150 mm, 5 microm particles), using a gradient method starting with mobile phase acetonitrile/methanol-citrate/pyrophosphate buffer (32:68, v/v). The total run time was 25 min. The fluorometric detector was operated at 260 nm (excitation) and 310 nm (emission). Pamidronate was used as the internal standard. The limit of quantification was 1 ng/ml using 3 ml of plasma. The intra- and inter-day precision expressed as the relative standard deviation was less than 15%. The assay was applied to the analysis of samples from a pharmacokinetic study. Following the oral administration of 70 mg of alendronate sodium to volunteers, the maximum plasma concentration (C(max)) and elimination half-life were 40.94 +/- 19.60 ng/ml and 1.67 +/- 0.50 h, respectively. The method was demonstrated to be highly feasible and reproducible for pharmacokinetic studies including bioequivalence test of alendronate sodium in humans.     

Development and validation of a simple reversed-phase high-performance liquid chromatography method for the determination of testosterone in serum of males

An isocratic high-performance liquid chromatographic method with detection at 234 nm was developed, optimized and validated for the determination of testosterone in human serum. Propylparaben was used as internal standard. A Hypersil BDS RP-C18 column (150 mmx4.6 mm, 5 microm), was equilibrated with a mobile phase composed of acetonitrile and water (35:65, v/v) and having a flow rate of 1 ml/min. The elution time for testosterone and internal standard was approximately 11.6 and 9.9 min, respectively. Calibration curves of testosterone in serum were linear in the concentration range of 1-20 ng/ml. Limits of detection and quantification in serum were 0.4 and 1.1 ng/ml, respectively. Recovery was greater than 92%. Intra- and inter-day relative standard deviation for testosterone in serum was less than 2.1 and 3.9%, respectively. This method was applied to the determination of testosterone serum levels of 12 healthy males and data were correlated with data obtained using a radioimmunoassay method.     

Quantification of trimetazidine in human plasma by liquid chromatography-electrospray ionization mass spectrometry and its application to a bioequivalence study

A rapid, sensitive and specific liquid chromatography-electrospray ionization mass spectrometric (LC-ESI-MS) method has been developed for the quantification of trimetazidine in human plasma. The analyte and the internal standard (pseudoephedrine) were extracted from plasma samples with n-hexane-dichloromethane (1:1, v/v) and analyzed on a C18 column. The chromatographic separation was achieved within 3.5 min using the mobile phase consisting of methanol/0.05% formic acid (80:20, v/v) and the flow rate was 1.0 ml/min. Ion signals m/z 181.0 and 148.0 were measured in the positive mode for trimetazidine and pseudoephedrine, respectively. The calibration curves were linear within the range of 0.4 to approximately 120 ng/ml. The lower limit of quantification (LLOQ) was 0.4 ng/ml with 0.5 ml plasma sample. The intra- and inter-day precisions were lower than 12% in terms of relative standard deviation (RSD). The inter-day relative error (RE) as determined from quality control samples (QCs), ranged from -1.4% to 3.3%. This validated method was successfully applied to the bioequivalent evaluation of two brands of trimetazidine tablets in 20 healthy volunteers.     

Simple high-performance liquid chromatographic determination of buspirone in human plasma

A simple, rapid and sensitive high-performance liquid chromatographic method for the determination of buspirone in plasma was developed. Buspirone was isolated from plasma using protein precipitation by acetonitrile and the recovery was complete. Citalopram was used as internal standard. The chromatographic conditions were as follows: analytical 125 x 4 mm, i.d. Nucleosil C18 column (5 microm particle size), mobile phase consisting of sodium dihydrogen phosphate buffer/acetonitrile (60:40, v/v) adjusted to pH 5.5 at a flow rate of 1.0 ml min(-1), UV detection at 235 nm. The quantification limit for buspirone in plasma was 0.5 ng ml(-1).The calibration curve was linear over the concentration range 0.5-10 ng ml(-1). The inter- and intra-day assay coefficients of variation were found to be less than 8%. The present validated method was successfully used for bioequivalence studies of buspirone in human subjects.     

Adaptation of solid phase extraction to an automated column switching method for online sample cleanup as the basis of a facile and sensitive high-performance liquid chromatographic assay for paclitaxel in human plasma

An improved method for assaying paclitaxel in human plasma by high-performance liquid chromatography (HPLC) with UV detection at 227 nm has been developed by adapting previously reported sample preparation methods and chromatographic conditions to facilitate semi-automated sample cleanup using a column switching technique. Manual sample manipulations were limited to isolating the drug and internal standard from plasma (1.0 ml) by liquid-liquid extraction using tert-butyl methyl ether. The sample extract was initially loaded onto a short cartridge column containing a cyanopropyl stationary phase. During the predetermined time interval that the drug and internal standard eluted from the cartridge, 1.50-2.20 min, a fully automated 6-position switching valve was used to direct the effluent onto an octylsilica analytical column. The same mobile phase, composed of acetonitrile-methanol-ammonium acetate buffer (pH 5.0; 20 mM) (76:19:105, v/v/v) and delivered at flow rate of 1.0 ml/min, was used for both separations. The overall retention times of paclitaxel and the internal standard were 10.9 and 18.1 min, respectively. The analytical method was thoroughly validated for quantitating paclitaxel in plasma at concentrations ranging from 6 to 586 nM (5-500 ng/ml). The lowest concentration of paclitaxel measured with acceptable day-to-day accuracy (100.2%) and precision (RSD 11.7%, n = 21, 5 months) was 6 nM (5 ng/ml). The sensitivity and selectivity of the assay proved to be more than adequate for monitoring steady-state plasma concentrations of the drug when administered to cancer patients as a 96 h continuous intravenous infusion in combination with other anticancer agents, such as doxorubicin and topotecan. Moreover, the heart-cutting procedure prevented the problematic introduction of interfering nonpolar plasma components onto the analytical column, thereby enhancing sample throughput while decreasing the technical demands of the assay. The method was found to be extremely reproducible and robust during extended use for the routine analysis of plasma specimens acquired from several clinical trials.     

Analysis of clonazepam in a tablet dosage form using smallbore HPLC

A stability indicating, reversed phase high-performance liquid chromatographic method utilizing a smallbore HPLC column has been developed for the determination of clonazepam in a commercial tablet dosage form. The use of a small bore column results in a substantial solvent savings, as well as a greater mass sensitivity, especially in the identification of degradation peaks in a chromatogram. The method involves ultraviolet detection at 254 nm and utilized a 150 x 3.0 mm i.d. column packed with 3 microm octyldecylsilane particles with a mobile phase of water methanol acetonitrile (40:30:30, v/v/v) at a flow rate of 400 microl min(-1) at ambient temperature, with and without the use of 1,2-dichlorobenzene as the internal standard. The current USP method for the analysis of clonazepam using a 300 x 3.9 mm i.d. conventional octyldecylsilane column was utilized as a comparison to the smallbore method. The retention times for clonazepam and the internal standard on the 3.0 mm i.d. column were 4.0 and 12.5 min, respectively. The intra- and interday RSDs on the 3.0 mm i.d. column were < 0.55% (n =4) using the internal standard, and < 0.19% (n = 4) without the internal standard at the lower limit of the standard curve, 50 microg ml(-1) and had a limit of detection of 24 ng ml(-1). The assay using the 3.0 mm i.d. column was shown to be suitable for measuring clonazepam in a tablet dosage form.     

Sensitive determination of nefopam and its metabolite desmethyl-nefopam in human biological fluids by HPLC

Nefopam (NEF) and desmethyl-nefopam (DMN) were assayed simultaneously in plasma, globule and urine samples using imipramine as internal standard. A liquid-liquid extraction procedure was coupled with a reverse phase high-performance liquid chromatography system. This system requires a mobile phase containing buffer (15 mM KH(2)PO(4) with 5 mM octane sulfonic acid: pH 3.7) and acetonitrile (77:33, v/v) through (flow rate=1.5 ml/min) a C(18) Symmetry column (150x4.6 I.D., 5 micrometer particle size: Waters) and a UV detector set at 210 nm. Internal standard was added to 1 ml of plasma or globule sample or 0.5 ml of urine sample, prior to the extraction under alkaline ambiance with n-hexane. The limits of quantification were 1 and 2 ng/ml for both molecules in plasma and globule, respectively; 5 and 10 ng/ml for NEF and DMN in urine, respectively. The method proved to be accurate and precise: the relative error at three concentrations ranged from -13.0 to +12.3% of the nominal concentration for all molecule and biological fluid; the within-day and between-day precision (relative standard deviation %) ranged from 1.0 to 10.1% for all the molecules and biological fluids. The method was linear between 1 and 60 ng/ml for both molecules in the plasma; 2 and 25 ng/ml for both molecules in the globule; 25 and 250 ng/ml for NEF and 50 and 500 ng/ml for DMN in the urine: correlation coefficients of calibration curves (determined by least-squares regression) of each molecule were higher than 0.992 whatever the biological fluid and during the pre-study and in-study validations. This method was successfully applied to a bio-availability study of NEF in healthy subjects.     

HPLC assay and pharmacokinetic study of atorvastatin in beagle dogs after oral administration of atorvastatin self-microemulsifying drug delivery system

A specific and accurate reversed-phase HPLC with UV detection was developed for the assay of atorvastatin in beagle dog plasma. Indomethacin was used as the internal standard. Atorvastatin was extracted by protein precipitation, the extracts were injected into a Kromasil C8 column (150 mm x 4.6 mm, 5 microm) with UV wavelength set at 270 nm. The mobile phase consisted of acetonitrile:0.1 mol/L ammonium acetate buffer (pH 4.0) (65:35% v/v) at a flow rate of 1.0 ml/min. The column was at ambient temperature (25 degrees C). The injection volume was 25 microl. The blank plasma did not interfere with the determination of atorvastatin and indomethacin. A good linear relationship was obtained between the peak area ratio of atorvastatin to indomethacin and the concentration of atorvastatin over the range of 0.05 to 2.5 microg/mL. The limit of quantification was 25 ng/mL, the limit of detection was 8 ng/ml. The total chromatographic analysis time was within 9 min. The method is accurate, precise and fast for the assay of atorvastatin in plasma following oral administration of an atorvastatin SMEDDS to healthy beagle dogs.     

High-performance liquid chromatographic method for the determination and pharmacokinetic study of oxypeucedanin hydrate and byak-angelicin after oral administration of Angelica dahurica extracts in mongrel dog plasma

A high-performance liquid chromatographic method was developed and validated for the determination and pharmacokinetic study of oxypeucedanin hydrate and byak-angelicin after oral administration of Angelica dahurica extracts in mongrel dog plasma. The coumarin components and the internal standard isopsoralen were extracted from plasma samples with the mixture of tert-butyl methyl ether and n-hexane (4:1, v/v). Chromatographic separation was performed on a C(18) column (200 mm x 4.6mm, 5 microm) with the mobile phase acetonitrile-methanol-water-acetic acid (20:15:65:2, v/v/v/v) at a flow-rate of 1.0 ml/min. Only the peak of oxypeucedanin hydrate and byak-angelicin could be detected in dog plasma after oral administration of ethanol extracts of A. dahurica mainly containing xanthotoxol, osthenol, imperatorin, oxypeucedanin hydrate and byak-angelicin. The calibration curves of oxypeucedanin hydrate and byak-angelicin were linear over a range of 22.08-8830.00 and 6.08-2430.00 ng/ml in dog plasma, respectively. The quantification limit of oxypeucedanin hydrate and byak-angelicin in dog plasma was 22.08 and 6.08 ng/ml, respectively. The intra- and inter-day precision was less than 7.6% and 8.5% and the accuracy was from 91.9% to 106.1%. The lowest absolute recoveries of oxypeucedanin hydrate and byak-angelicin were 85.7% and 87.0%, respectively. The method was successfully applied to the pharmacokinetic studies of oxypeucedanin hydrate and byak-angelicin in dog plasma after oral administration of ethanol extracts from A. dahurica.     

A simple and rapid HPLC method for the determination of atorvastatin in human plasma with UV detection and its application to pharmacokinetic studies

A rapid and sensitive high-performance liquid chromatographic method for the determination of atorvastatin (CAS 134523-00-5) in plasma was developed in this study. Atorvastatin was isolated from plasma using protein precipitation by acetonitrile. Diltiazem (CAS 33286-22-5) was used as internal standard. The chromatographic conditions were as follows: analytical 125 x 4 mm (i.d.) Nucleosil C8 column (5 microm particle size), mobile phase consisting of sodium dihydrogen phosphate buffer-acetonitrile (60:40, v/v) adjusted to pH 5.5 at a flow rate of 1.5 ml/min, UV detection at 245 nm. The detection limit for atorvastatin in plasma was 1 ng ml(-1). The calibration curve was linear over the concentration range 20-800 ng ml(-1). The recovery was complete. The inter-day and intra-day assay coefficients of variation were found to be less than 7%. The present validated method was successfully used for pharmacokinetic studies of atorvastatin in human subjects.     

Determination of lovastatin in human plasma by ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry and its application in a pharmacokinetic study

A selective, rapid and sensitive ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the quantitative determination of lovastatin in human plasma and its application in a pharmacokinetic study. With mycophenolate mofetil as internal standard, sample pretreatment involved a one-step extraction with tert-butyl methyl ether of 0.2 ml plasma. The analysis was carried out on an ACQUITY UPLCTM BEH C18 column (50 mm x 2.1 mm, i.d., 1.7 microm) with flow rate of 0.35 ml/min. The mobile phase was 20% water and 80% acetonitrile (v/v). The detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode via electrospray ionization (ESI). Linear calibration curves were obtained in the concentration range of 0.08-24.50 ng/ml, with a lower limit of quantification of 0.08 ng/ml. The intra- and inter-day precision (RSD) values were below 15% and accuracy (RE) was -7.6 to 9.3% at all QC levels. The method was applicable to clinical pharmacokinetic study of lovastatin in healthy volunteers following oral administration.     

Determination of thiencynonate by liquid chromatographic-mass spectrometry and its application to pharmacokinetics in rats

A sensitive and specific high-performance liquid chromatography-tandem mass spectrometry method (LC/ESI/MS) was developed and validated for the identification and quantification of the novel lead compound of anticholinergic drug thiencynonate in rat plasma. The analytes were determined using positive electrospray ionization mass spectrometry in the selected reaction ion monitoring (SRM). The chromatography separation was on BetaBasic-18 column (150 mm x 2.1 mm i.d., 3 microm). The mobile phase was composed of methanol-water (70:30, v/v), containing 0.5 per thousand formic acid, which was pumped at a flow rate of 0.2 ml/min. Phencynonate was selected as the internal standard (IS). Simultaneous MS detection of thiencynonate and IS was performed at m/z 364.4 (thiencynonate), m/z 358 (phencynonate), and the SRM of the two compounds were both at 156. Thiencynonate eluted at approximately 2.8 min, phencynonate eluted at approximately 2.9 min and no endogenous materials interfered with their measurement. Linearity was obtained over the concentration range of 1-100 ng/ml in rat plasma. The lower limit of quantification (LLOQ) was reproducible at 1 ng/ml in rat plasma. The precision measured was obtained from 2.47 to 9.28% in rat plasma. Extraction recoveries were in the range of 67.63-76.76% in plasma. This method was successfully applied to the identification and quantification of thiencynonate in pharmacokinetic studies.     

A rapid reversed phase high performance liquid chromatographic method for determination of etoposide (VP-16) in human plasma

A rapid, simple and sensitive isocratic High Performance Liquid Chromatography (HPLC) method was developed to measure the concentration of etoposide in plasma samples with UV detection at 220 nm. The method uses a Bondapac C18 column at 60 degrees C. The mobile phase consists of Methanol: water (45:55 v/v) at a flow rate of 2.8 ml/min. Phenacetin was used as an internal standard. The plasma samples were extracted using ether with the organic layer evaporated under nitrogen. The residue was dissolved in 200 microl methanol with 20 microl injected into the HPLC column. The extraction method showed a recovery of 91.5+/-3% for etoposide. In this system, the retention time of phenacetin and etoposide were 3.3 and 4.4 min, respectively. The limit of detection of etoposide in plasma is 20 ng/ml and the limit of quantitation is 40 ng/ml. This analytical method has very good reproducibility (8.1% between-day variability at a concentration of 50 ng/ml). It is a fast, sensitive and economic method applicable for clinical and pharmacokinetic studies.     

Validated HPLC method for determination of PAT-5A, an insulin sensitizing agent, in rat plasma

A high performance liquid chromatographic method for the determination of PAT-5A (a potent insulin sensitizer) using DRF-2095 (a thiazolidinedione) as internal standard (I.S.) is described. A 1:1 v/v ethylacetate and dichloromethane solvent mixture was used for extraction of PAT-5A from plasma. A Kromasil KR100-5C18-250A, 5 microm, 4.6 x 250 mm SS column was used for the analysis. Mobile phase consisting of sodium dihydrogen phosphate (pH 4.0, 0.05 M) and methanol mixture (25:75, v/v) was used at a flow rate of 1.0 ml/min. The eluate was monitored using a UV detector set at 345 nm. Ratio of peak area of analyte to I.S. was used for quantification of plasma samples. Using this method the absolute recovery of PAT-5A from rat plasma was > 90% and the limit of quantification was 0.05 microg/ml. The intra-day relative standard deviation (RSD) ranged from 2.19 to 4.98% at 1.0 microg/ml, 1.05 to 3.68% at 10.0 microg/ml and 3.14 to 5.08% at 50 microg/ml. The inter-day RSD were 1.6, 2.24 and 1.54% at 1, 10 and 50 microg/ml, respectively. The method was applied to measure the plasma concentrations of PAT-5A in pharmacokinetic and bioavailability studies in male Wistar rats.     

HPLC assay for albendazole and metabolites in human plasma for clinical pharmacokinetic studies

A sensitive and selective HPLC chromatography method using UV detection (295 nm) was developed for the determination of albendazole, albendazole sulfoxide (ABZSO), and albendazole sulfone (ABZSO2) in human plasma. Albendazole, ABZSO, ABZSO2, and the internal standard, oxibendazole, were extracted from human plasma by loading onto a conditioned C(18) SPE cartridge, rinsing with 15% methanol, and eluting with 90% methanol. Samples were evaporated under a stream of nitrogen, reconstituted with mobile phase, 1.25% triethylamine in water-methanol-acetonitrile (72:15:13, v/v/v) (pH* 3.1), and injected onto a Waters muBondapak Phenyl 3.9 x 300 mm HPLC column. Mobile phase flow rate was 1.0 ml/min. The retention times of albendazole, ABZSO, ABZSO2, and the internal standard were approximately 24.4, 7.9, 13.4, and 11.3 min, respectively. Total run time was 30 min. The assay was linear for concentration ranges in human plasma of 20-600 ng/ml for albendazole, 20-1000 ng/ml for ABZSO, and 20-300 ng/ml for ABZSO2. The analysis of quality control samples demonstrated excellent precision. Coefficients of variation for albendazole (20, 400, 600 ng/ml) were 6.7, 8.1 and 7.0%; ABZSO (20, 400, 800 ng/ml) were 6.0, 8.5 and 5.9%; ABZSO2 (20, 150, 300 ng/ml) were 3.1, 3.9 and 2.3%, respectively. The method appears to be robust and has been applied to a pharmacokinetic study of albendazole in healthy volunteers.