Sensitive determination of omeprazole and its two main metabolites in human plasma by column-switching high-performance liquid chromatography: application to pharmacokinetic study in relation to CYP2C19 genotypes

A simple and sensitive column-switching high-performance liquid chromatographic method was developed for the simultaneous determination of omeprazole and its two main metabolites, 5-hydroxyomeprazole and omeprazole sulfone, in human plasma. Omeprazole, its two metabolites and lansoprazol as an internal standard were extracted from 1 ml of alkalinized plasma sample using diethyl ether-dichloromethane (45:55, v/v). The extract was injected into a column I (TSK-PW precolumn, 10 microm, 35 mm x 4.6 mm i.d.) for clean-up and column II (Inertsil ODS-80A column, 5 microm, 150 mm x 4.6mm i.d.) for separation. The mobile phase consisted of phosphate buffer-acetonitrile (92:8 v/v, pH 7.0) for clean-up and phosphate buffer-acetonitrile-methanol (65:30:5 v/v/v, pH 6.5) for separation, respectively. The peak was detected with an ultraviolet detector set at a wavelength of 302 nm, and total time for chromatographic separation was approximately 25 min. The validated concentration ranges of this method were 3-2000 ng/ml for omeprazole, 3-50 ng/ml for 5-hydroxyomeprazole and 3-1000 ng/ml for omeprazole sulfone. Mean recoveries were 84.3% for omeprazole, 64.3% for 5-hydroxyomeprazole and 86.1% for omeprazole sulfone. Intra- and inter-day coefficient variations were less than 5.1 and 6.6% for omeprazole, 4.6 and 5.0% for 5-hydroxyomeprazole and 4.6 and 4.9% for omeprazole sulfone at the different concentrations. The limits of quantification were 3 ng/ml for omeprazole and its metabolites. This method was suitable for use in pharmacokinetic studies in human volunteers, and provides a useful tool for measuring CYP2C19 activity.     

Determination of pyronaridine in blood plasma by high-performance liquid chromatography for application in clinical pharmacological studies

A method is described for the determination of pyronaridine in plasma using high-performance liquid chromatography with fluorescence detection. The method involves liquid-liquid extraction with phosphate buffer (pH 6.0, 0.05 M) and diethyl ether-hexane (70:30%, v/v) and chromatographic separation on a C₁₈ column (Nucleosil, 250 × 4.6 mm I.D., 5 μm particle size) with acetonitrile-0.05 M phosphate buffer pH 6.0 (60:40%, v/v) as the mobile phase (1 ml/min) and detection by fluorescence (λ_ex = 267 nm, λ_em = 443 nm). The detector response is linear up to 1000 ng and the overall recoveries pyronaridine and quinine were 90.0 and 60.3%, respectively. The assay procedure was adequately sensitive to measure 10 ng/ml pyronaridine in plasma samples with acceptable precision (< 15% C.V.). The method was found to be suitable for use in clinical pharmacological studies.     

Development and validation of a liquid chromatography-tandem mass spectrometric assay for Eplerenone and its hydrolyzed metabolite in human plasma

A sensitive and specific liquid chromatography-tandem mass spectrometry assay was developed to quantify the first selective aldosterone blocker Eplerenone (I) and its hydrolyzed metabolite (II) in human plasma. The analytes (I, II) and their stable isotope-labeled analogues as internal standards were extracted on a C(18) solid-phase extraction cartridge using a Zymark RapidTrace automation system. The chromatographic separation was carried out on a narrow-bore reversed-phase Zorbax XDB-C(8) HPLC column with a mobile phase of acetonitrile/water (40:60, v/v) containing 10 mM ammonium acetate (pH 7.4). The analytes were ionized using negative-to-positive switch electrospray mass spectrometry, then detected by multiple reaction monitoring with a tandem mass spectrometer. The precursor to product ion transitions of m/z 415-->163 and m/z 431-->337 was used to measure I and II, respectively. The assay exhibited a linear dynamic range of 10-2500 ng/ml of plasma for both I and II. The lower limit of quantification was 10 ng/ml for I and II. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A throughput of 80 human plasma standards and samples per run was achieved with run time of 5 min for each injection. The assay has been successfully used in analyses of human plasma samples to support clinical studies.     

Analysis of Ecteinascidin 743, a new potent marine-derived anticancer drug, in human plasma by high-performance liquid chromatography in combination with solid-phase extraction

A reversed-phase high-performance liquid chromatographic method has been developed and validated for the quantification of the novel anticancer drug Ecteinascidin 743 in human plasma. The sample pretreatment of the plasma samples involved a solid-phase extraction (SPE) on cyano columns. Propyl-p-hydroxybenzoate was added after the sample pretreatment to correct for variability in injection volumes. The separation was performed on a Zorbax SB-C₁₈ column (75×4.6 mm I.D., particle size 3.5 μm) with acetonitrile–25 mM phosphate buffer, pH 5.0 (70:30, v/v) as the mobile phase. The flow-rate was 1.0 ml/min and the eluent was monitored at 210 nm. 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 1.0 ng/ml using 500 μl of plasma. The overall recovery of the sample pretreatment procedure for Ecteinascidin 743 was 87.0±5.9%. The drug was found to be stable in human plasma at −30°C for at least 2 months. At room temperature Ecteinascidin 743 was stable in human plasma for 5 h at most.     

Determination of hydroxyurea in plasma and peritoneal fluid by high-performance liquid chromatography using electrochemical detection

A sensitive method has been developed for the determination of hydroxyurea in plasma and peritoneal fluid using reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection. Plasma or peritoneal fluid samples were treated with acetonitrile to precipitate proteins then injected to the HPLC. A C₁₈ analytical column was used to separate hydroxyurea from interfering substances in the biological matrix. The mobile phase, consisting of 0.2 M sodium perchlorate–methanol (95:5, v/v) adjusted to pH 5.0, was delivered isocratically at a flow-rate of 1 ml/min and hydroxyurea was detected using a glassy-carbon electrode operating at an applied potential of +800 mV. Hydroxyurea eluted with a retention time of 3 min. The cycle time for analysis is short and the assay precision is acceptable (C.V. plasma=1.4–3.9%, C.V. peritoneal fluid=2.1–9.7%). The method has been validated and is linear from 25 to 400 ng/ml in plasma and 5 to 30 ng/ml in peritoneal fluid. The method has been shown to be applicable for pharmacokinetic studies.     

Stereoselective determination of cisapride, a prokinetic agent, in human plasma by chiral high-performance liquid chromatography with ultraviolet detection: application to pharmacokinetic study

We have developed a simple, sensitive, specific and reproducible stereoselective high-performance liquid chromatography technique for analytical separation of cisapride enantiomers and measurement of cisapride enantiomers in human plasma. A chiral analytical column (ChiralCel OJ) was used with a mobile phase consisting of ethanol–hexane–diethylamine (35:64.5:0.5, v/v/v). This assay method was linear over a range of concentrations (5–125 ng/ml) of each enantiomer. The limit of quantification was 5 ng/ml in human plasma for both cisapride enantiomers, while the limit of detection was 1 ng/ml. Intra- and inter-day C.V.s did not exceed 15% for all concentrations except at 12.5 ng/ml for EII (+)-cisapride, which was 20 and 19%, respectively. The clinical utility of the method was demonstrated in a pharmacokinetic study of normal volunteers who received a 20 mg single oral dose of racemic cisapride. The preliminary pharmacokinetic data obtained using the method we describe here provide evidence for the first time that cisapride exhibits stereoselective disposition.     

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%.     

Sensitive determination of clarithromycin in human plasma by high-performance liquid chromatography with spectrophotometric detection

A rapid, selective and sensitive high-performance liquid chromatographic method with spectrophotometric detection was developed for the determination of clarithromycin in human plasma. Liquid-liquid extraction of clarithromycin and norverapamil (as internal standard) from plasma samples was performed with n-hexane/1-butanol (98:2, v/v) in alkaline condition followed by back-extraction into diluted acetic acid. Chromatography was carried out using a CN column (250 mm x 4.6 mm, 5 microm) under isocratic elution with acetonitrile-50 mM aqueous sodium dihydrogen phosphate (32:68, v/v), pH 4.5. Detection was made at 205 nm and analyses were run at a flow-rate of 1.0 ml/min at 40 degrees C. The analysis time was less than 11 min. The method was specific and sensitive with a quantification limit of 31.25 ng/ml and a detection limit of 10 ng/ml in plasma. The mean absolute recovery of clarithromycin from plasma was 95.9%, while the intra- and inter-day coefficient of variation and percent error values of the assay method were all less than 9.5%. Linearity was assessed in the range of 31.25-2000 ng/ml in plasma with a correlation coefficient of greater than 0.999. The method was used to analyze several hundred human plasma samples for bioavailability studies.     

Determination of donepezil, an acetylcholinesterase inhibitor, in human plasma by high-performance liquid chromatography with ultraviolet absorbance detection

A simple and sensitive high-performance liquid chromatographic (HPLC) method with UV absorbance detection is described for the quantification of donepezil, a centrally and selectively acting acetyleholinesterase inhibitor, in human plasma. After sample alkalinization with 0.5 ml of NaOH (0.1 M), the test compound was extracted from I ml of plasma using isopropanol-hexane (3:97, v/v). The organic phase was back-extracted with 75 microl of HCl (0.1 M) and 50 microl of the acid solution was injected into a C18 STR ODS-II analytical column (5 microm, 150x4.6 mm I.D.). The mobile phase consisted of phosphate buffer (0.02 M, pH 4.6), perchloric acid (6 M) and acetonitrile (59.5:0.5:40, v/v) and was delivered at a flow-rate of 1.0 ml/min at 40 degrees C. The peak was detected using a UV detector set at 315 nm, and the total time for a chromatographic separation was approximately 8 min. The method was validated for the concentration range 3-90 ng/ml. Mean recoveries were 89-98%. Intra- and inter-day relative standard deviations were less than 7.3 and 7.6%, respectively, at the concentrations ranging from 3 to 90 ng/ml. The method shows good specificity with respect to commonly prescribed psychotropic drugs, and it could be successfully applied for pharmacokinetic studies and therapeutic drug monitoring.     

Sensitive liquid chromatography assay with ultraviolet detection for a new phosphodiesterase V inhibitor, DA-8159, in human plasma and urine

A sensitive high-performance liquid chromatographic (HPLC) method with ultraviolet absorption detection (292 nm) was developed and validated for the determination of the new phosphodiesterase V inhibitor, DA-8159 (DA), in human plasma and urine. A single step liquid-liquid extraction procedure using ethyl ether was performed to recover DA and the internal standard (sildenafil citrate) from 1.0 ml of biological matrices combined with 200 microl of 0.1M sodium carbonate buffer. A Capcell Pak C18 UG120 column (150 mm x 4.6 mm I.D., 5 microm) was used as a stationary phase and the mobile phase consisted of 30% acetonitrile and 70% 20mM potassium phosphate buffer (pH 4.5) at a flow rate of 1.0 ml/min. The lower limit for quantification was 5 ng/ml for plasma and 10 ng/ml for urine samples. Within- and between-run accuracy and precision were < or =15 and < or =10%, respectively, in both plasma and urine samples. The recovery of DA from human plasma and urine was greater than 70%. Separate stability studies showed that DA is stable under the conditions of analysis. This validated assay was used for the pharmacokinetic analysis of DA during a phase I, rising dose study.     

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.     

Quantitation of tadalafil in human plasma by liquid chromatography-tandem mass spectrometry with electrospray ionization

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantitation of tadalafil (I) in human plasma, a new selective, reversible phosphodiesterase 5 inhibitor. The analyte and internal standard (sildenafil, II) were extracted by liquid-liquid extraction with diethyl ether/dichloromethane (70/30, v/v) using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on reverse phase Xterra MS C18 column with a mobile phase of 10mM ammonium formate/acetonitrile (10/90, v/v, pH adjusted to 3.0 with formic acid). The protonate of analyte was quantitated in positive ionization by multiple reaction monitoring with a mass spectrometer. The mass transitions m/z 390.4 --> 268.0 and m/z 475.5 --> 58.3 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 10-1000 ng/mL for tadalafil in human plasma. The lower limit of quantitation was 10 ng/mL with a relative standard deviation of less than 15%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. Run time of 1.2 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.     

Determination of a cyclooxygenase II inhibitor in human plasma by capillary gas chromatography with mass spectrometric detection

Sensitive methods based on capillary gas chromatography (GC) with mass spectrometric (MS) detection in a selected-ion monitoring mode (SIM) for the determination of a cyclooxygenase II (COX-II) inhibitor (3-isopropoxy-4-(4-methanesulfonylphenyl)-5,5'-dimethyl-5H-furan-2-one, I) in human plasma, in two concentration ranges of 0.1-20 and 5-1000 ng/ml, are described. Following liquid-liquid extraction, the residue, after evaporation of the organic phase to dryness, was reconstituted in acetonitrile (20 l) and part of the extract (1 l) was analyzed by GC/MS/SIM. The drug (I) and internal standard (II) were separated on a 25 mx0.2 mm capillary column with HP Ultra 1 (100% dimethylpolysiloxane, 0.33 m) phase and analyzed by MS/SIM monitoring ions at m/z 237 and 282 for I and II, respectively. The standard curve was linear within the lower concentration range of 0.1-20 ng/ml and the lower limit of quantification (LLOQ) in plasma was 0.1 ng/ml. Intraday coefficients of variation (CV, n=5) were 8.9, 4.2, 5.7, 3.1, 1.9, 1.9, and 4.4% at 0.1, 0.2, 0.5, 1.0, 5.0, 10, and 20 ng/ml, respectively. The standard curve was also linear within the higher concentration range of 5-1000 ng/ml and the LLOQ in plasma was 5 ng/ml. Intraday coefficients of variation (CV, n=5) were all below 9% at all concentrations within the standard curve range. The accuracy for I in human plasma was 91-112% and the recovery of I and II was greater than 70% at all concentrations within both standard curve ranges. The details of the assay methodology are presented.     

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.     

Sensitive isocratic liquid chromatographic assay for the determination of 5, 10, 15, 20-tetra(m-hydroxyphenyl)chlorin in plasma and tissue with electrochemical detection

A simple extraction procedure and a sensitive high-performance liquid chromatographic (HPLC) method are described for the determination of the photodynamic therapeutic agent 5, 10, 15, 20-tetra(m-hydroxyphenyl)chlorin (mTHPC) in plasma and tumour tissue. Reversed-phase high-performance liquid chromatography was performed on a C₁₈ column (70×4.6 mm I.D.) with a mobile phase of 0.01 M potassium dihydrogenphosphate buffer, pH 2.5-acetonitrile (55:45, v/v) and a coulometric detection (+0.80 V). The mean recoveries of mTHPC in the concentration ranges (5–2000 and 10–1000 ng/ml) were 90 and 89% for plasma and tumour samples, respectively. The procedure for plasma and tissue preparation involved solvent precipitation using methanol combined with ammonia solution and dimethyl sulphoxide (4, 0.2, 0.1, v/v/v) and (2, 0.1, 0.1, v/v/v) for plasma and tissue, respectively. For mTHPC at concentrations ranging from 5 to 2000 ng/ml, the within-day relative standard deviations, based on triplicate determinations were less than 8% and the between-day relative standard deviations calculated by performing extraction procedure of plasma samples on three different days ranged from 3 to 18%. This highly sensitive method, 5 and 10 ng/ml for plasma and tissue respectively, was applied successfully to the determination of mTHPC in mouse tumours for pharmacokinetic studies.     

Simultaneous determination of lipoic acid (LA) and dihydrolipoic acid (DHLA) in human plasma using high-performance liquid chromatography coupled with electrochemical detection

A fast, simple, and a reliable high-performance liquid chromatography linked with electrochemical detector (HPLC-ECD) method for the assessment of lipoic acid (LA) and dihydrolipoic acid (DHLA) in plasma was developed using naproxen sodium as an internal standard (IS) and validated according to standard guidelines. Extraction of both analytes and IS from plasma (250 μl) was carried out with a single step liquid-liquid extraction applying dichloromethane. The separated organic layer was dried under stream of nitrogen at 40°C and the residue was reconstituted with the mobile phase. Complete separation of both compounds and IS at 30°C on Discovery HS C18 RP column (250 mm × 4.6 mm, 5 μm) was achieved in 9 min using acetonitrile: 0.05 M phosphate buffer (pH 2.4 adjusted with phosphoric acid) (52:48, v/v) as a mobile phase pumped at flow rate of 1.5 ml min(-1) using electrochemical detector in DC mode at the detector potential of 1.0 V. The limit of detection and limit of quantification for lipoic acid were 500 pg/ml and 3 ng/ml, and for dihydrolipoic acid were 3 ng/ml and 10 ng/ml, respectively. The absolute recoveries of lipoic acid and dihydrolipoic acid determined on three nominal concentrations were in the range of 93.40-97.06, and 93.00-97.10, respectively. Similarly coefficient of variations (% CV) for both intra-day and inter-day were between 0.829 and 3.097% for lipoic acid and between 1.620 and 5.681% for dihydrolipoic acid, respectively. This validated method was applied for the analysis of lipoic acid/dihydrolipoic acid in the plasma of human volunteers and will be used for the quantification of these compounds in patients with oxidative stress induced pathologies.     

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.     

Liquid chromatographic analysis of the cis(Z)- and trans(E)-isomers of clopenthixol in human plasma using a novel solid phase extraction procedure

A simple and highly sensitive high-performance liquid chromatographic (HPLC) method for the simultaneous determination of cis(Z)-clopenthixol and trans(E)-clopenthixol in human plasma has been developed. The chromatographic analysis was carried out isocratically on a reversed-phase column (C(8) 150 x 4.6 mm I.D., 5 microm) using a mixture of 25 mM phosphate buffer and acetonitrile (65:35 v/v, pH* 3.0) as the mobile phase, and ultraviolet detection at 230 nm. Plasma sample pretreatment was accomplished by means of an original solid-phase extraction (SPE) procedure carried out on cyanopropyl cartridges, with a high extraction yield and good selectivity. Under the optimum conditions, calibration graphs of spiked human plasma samples were obtained over the concentration ranges 1-300 ng ml(-1) for cis(Z)-clopenthixol and 1-200 ng ml(-1) for trans(E)-clopenthixol. The limit of detection (LOD) was 0.3 ng ml(-1) for both cis(Z)- and trans(E)-isomers of clopenthixol. The method was successfully applied to the determination of cis(Z)-clopenthixol and trans(E)-clopenthixol in plasma samples of schizophrenic patients undergoing therapy with zuclopenthixol.     

Quantitation of tamsulosin in human plasma by liquid chromatography-electrospray ionization mass spectrometry

A highly sensitive method for quantitation of tamsulosin in human plasma using 1-(2,6-dimethyl-3-hydroxylphenoxy)-2-(3,4-methoxyphenylethylamino)-propane hydrochloride as the internal standard (I.S.) was established using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). After alkalization with saturated sodium bicarbonate, plasma were extracted by ethyl acetate and separated by HPLC on a C18 reversed-phase column using a mobile phase of methanol-water-acetic acid-triethylamine (620:380:1.5:1.5, v/v). Analytes were quantitated using positive electrospray ionization in a quadrupole spectrometer. LC-ESI-MS was performed in the selected ion monitoring (SIM) mode using target ions at m/z 228 for tamsulosin and m/z 222 for the I.S. Calibration curves, which were linear over the range 0.2-30 ng/ml, were analyzed contemporaneously with each batch of samples, along with low (0.5 ng/ml), medium (3 ng/ml) and high (30 ng/ml) quality control samples. The intra- and inter-assay variability ranged from 2.14 to 8.87% for the low, medium and high quality control samples. The extraction recovery of tamsulosin from plasma was in the range of 84.2-94.5%. The method has been used successfully to study tamsulosin pharmacokinetics in adult humans.