Liquid/liquid extraction using 96-well plate format in conjunction with hydrophilic interaction liquid chromatography-tandem mass spectrometry method for the analysis of fluconazole in human plasma

A bioanalytical method using automated sample transferring, automated liquid/liquid extraction (LLE) and hydrophilic interaction liquid chromatography-tandem mass spectrometry was developed for the determination of fluconazole in human plasma. Samples of 0.05 ml were transferred into 96-well plate using automatic liquid handler (Multiprobe II). Automated LLE was carried out on a 96-channel programmable liquid handling workstation (Quadra 96) using methyl-tetra butyl ether as the extraction solvent. The extract was evaporated to dryness, reconstituted, and injected onto a silica column using an aqueous-organic mobile phase. The chromatographic run time was 2.0 min per injection, with retention times of 1.47 and 1.44 min for fluconazole and internal standard (IS) ritonavir, respectively. The detection was by monitoring fluconazole at m/z 307-->238 and IS at m/z 721-->296, respectively. The standard curve range was 0.5-100 ng ml(-1). The inter-day precision and accuracy of the quality control samples were <7.1% relative standard deviation and <2.2% relative error.     

Automated 96-well liquid-liquid back extraction liquid chromatography-tandem mass spectrometry method for the determination of ABT-202 in human plasma

A high-throughput bioanalytical method using automated sample transferring, automated liquid-liquid back extraction and liquid chromatography-tandem mass spectrometry was developed in a GLP regulated environment for the determination of ABT-202 in human plasma. Samples of 0.30 ml were transferred into 96-well plate using an automatic liquid handler. Automated liquid-liquid extraction (LLE) was carried out on a 96-channel programmable liquid handling workstation using methyl tert-butyl ether as the extraction solvent. A dual-HPLC with single mass spectrometer configuration was utilized to provide a reliable and routine means to increase sample throughput. The standard curve range was 0.38-95.02 ng/ml. There was no interference from endogenous components in the blank plasma tested. The accuracy (% bias) at the lower limit of quantitation (LLOQ) was 7.7% and the precision (% CV) for samples at the LLOQ was 4.7%. The inter-day % CV and % bias of the quality control samples were < or = 6.8 and < or = 7.6%, respectively. Coefficients of determination, a measure of linearity, ranged from 0.994 to 0.997. The method was accurate and reproducible and was successfully applied to generate plasma concentration-time profiles for human subjects after low oral doses of the compound.     

Quantitative analysis of PD 0332991 in xenograft mouse tumor tissue by a 96-well supported liquid extraction format and liquid chromatography/mass spectrometry

Phase II attrition of clinical candidates in the drug development cycle is currently a major issue facing the pharmaceutical industry. To decrease phase II attrition, there is an increased emphasis on validation of mechanism of action, development of efficacy models and measurement of drug levels at the site of action. PD 0332991, a highly specific inhibitor of cyclin-dependent kinase 4 (CDK-4) is currently in clinical development for the treatment of solid tumor. A clinical presurgical study will be required to better understand how PD 0332991 affects signaling pathways and how the intratumoral concentration of PD 0332991 correlates with plasma PK parameters and molecular alterations in breast cancer tissues after PD 0332991 treatment. Before conducting such a clinical study, it is important to evaluate PD 0332991 levels in tumor tissue samples from a xenograft mouse model for the determination of drug exposure at the site of action. Therefore, the objectives of this study were (1) to develop and validate a sensitive LC–MS/MS method to quantify PD 0332991 in mouse tumor tissues from MDA-MB-231-Luc human breast tumor xenografts in SCID-beige mice; (2) to quantify PD 0332991 levels in mouse tumor tissues after oral administration of PD 0332991 at 10 and 100 mg/kg using the validated LC–MS/MS method. Both liquid–liquid extraction (LLE) and supported liquid extraction (SLE) in a 96-well format were developed and evaluated to achieve optimal extraction recovery with minimal matrix effects. The newly developed SLE method is more efficient (speed and ease) and demonstrates comparable recovery (93.1–100% at three different concentrations) compared to the traditional LLE method. The validated LC–MS/MS for PD 032291 in mouse tumor tissue homogenate method exhibited a linear dynamic range of 0.1–100 ng/mL with inter-day accuracy and precision within 15%. The validated method was successfully applied to measure PD 0332991 levels in tumor tissues in MDA-MB-231-Luc human breast tumor xenografts in SCID beige mice. The mean tumor concentrations at 6 h post-oral PD 0332991 administration at 10 and 100 mg/kg were 1793 (±1008) and 25,163 (±3959) ng/g, respectively.     

高效液相色谱-串联质谱法测定人血浆中色氨酸及其代谢物浓度

目的建立一种基于高效液相色谱-串联质谱(LC-MS/MS)技术同时快速测定人血浆中色氨酸及其代谢产物(犬尿氨酸、犬尿喹啉酸和吲哚丙酸)含量的方法。方法采用甲醇/乙腈(v/v,50/50)沉淀蛋白,以色氨酸-d_5为内标,色谱柱:Ultimate XB-C_(18) HPLC柱(2.1 mm×100 mm,3μm),流动相:水-甲醇(45/55,水相含5 mmol/L醋酸铵和0.2%甲酸),流速:0.3 ml/min,柱温:40℃,分析时间共3 min。质谱采用API4000 QTrap三重四极杆质谱仪的正离子多反应监测模式监测。考察该方法的专属性、线性及定量范围、精密度与准确度、回收率与基质效应以及稳定性。结果色氨酸、犬尿氨酸、犬尿喹啉酸及吲哚丙酸的线性范围分别在100～2×10~4、25～5 000、5～1 000、10～2 000 ng/ml;平均回收率均>90%;日内和日间精密度(RSD)和准确度(RE)均小于15%;稳定性良好。该方法成功测定了90例冠心病患者血浆中的色氨酸、犬尿氨酸、犬尿喹啉酸及吲哚丙酸的浓度。结论该方法简便、快捷、灵敏,可用于人体血浆中色氨酸及其代谢产物浓度的测定。     

A 96-well single-pot liquid-liquid extraction, hydrophilic interaction liquid chromatography-mass spectrometry method for the determination of muraglitazar in human plasma

A single-pot liquid-liquid extraction (LLE) with hydrophilic interaction liquid chromatography/tandem mass spectrometry (HILIC/MS/MS) method has been developed and validated for the determination of muraglitazar, a hydrophobic diabetes drug, in human plasma. To 0.050 ml of each plasma sample in a 96-well plate, the internal standard solution in acetonitrile and toluene were added to extract the compound of interest. The plate was vortexed, followed by centrifugation. The organic layer was then directly injected into an LC/MS/MS system. Chromatographic separation was achieved isocratically on a Thermohypersil_Keystone, Hypersil silica column (3 mmx50 mm, 3 microm). The mobile phase contained 85% of methyl t-butyl ether and 15% of 90/10 (v/v) acetonitrile/water with 0.3% trifluoroacetic acid. Post-column mobile phase of 50/50 (v/v) acetonitrile/water containing 0.1% formic acid was added. Detection was by positive ion electrospray tandem mass spectrometry on a Sciex API 4000. The standard curve, ranged from 1 to 1000 ng/ml, was fitted to a 1/x weighted quadratic regression model. This single-pot LLE approach effectively eliminated time-consuming organic layer transfer, dry-down, and sample reconstitution steps, which are essential for a conventional liquid-liquid extraction procedure. The modified mobile phase was more compatible with the direct injection of the commonly used extraction solvents in LLE. Furthermore, the modified mobile phase improved the retention of muraglitazar, a hydrophobic compound, on the normal phase silica column. The validation results demonstrated that this method was rugged and suitable for analyzing muraglitazar in human plasma. In comparison with a revised-phase LC/MS/MS method, this single-pot LLE, HILIC/MS/MS method improved the detection sensitivity by more than four-fold based upon the LLOQ signal to noise ratio. This approach may be applied to other hydrophobic compounds with proper modification of the mobile phase compositions.     

Comparison of solid-phase microextraction and liquid-liquid extraction in 96-well format for the determination of a drug compound in human plasma by liquid chromatography with tandem mass spectrometric detection

Two sensitive and selective methods based on solid phase microextraction (SPME) and liquid-liquid extraction (LLE) in 96-well format, in combination with high performance liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection have been developed to determine a model drug compound in human plasma. Both assays were performed on an Applied Biosystems-Sciex API 4000 tandem mass spectrometer interfaced with a turbo ion-spray probe and operated in the negative ionization mode. A lower limit of quantitation (LLOQ) of 1 ng/mL achieved when 0.25 mL of human plasma was processed. In both methods, a stable isotope labeled internal standard was utilized. The methods were validated in the concentration range of 1-500 ng/mL. The intraday precision (%C.V.) of the method using LLE was 0.8% at LLOQ, and was equal to or lower than 3.3% at all other concentrations, while the intraday precision (%C.V.) of the method using SPME was 6.9% at LLOQ, and was equal to or lower than 5.7% at all other concentrations. Based on the direct comparison of the two methods and their successful applications in clinical sample analysis, it may be concluded that SPME may be considered and used as an alternative approach for quantitative determination of drugs in pharmacokinetic studies.     

Quantitative determination of paclitaxel in human plasma using semi-automated liquid-liquid extraction in conjunction with liquid chromatography/tandem mass spectrometry

This paper describes a high-throughput sample preparation procedure combined with LC-MS/MS analysis to measure paclitaxel in human plasma. Paclitaxel and an internal standard were extracted from plasma by a semi-automated robotic method using liquid-liquid extraction. Thereafter compounds were separated on a RP C18 column. Detection was by a PE Sciex API 3000 mass spectrometer equipped with a TurboIonSpray interface. The compounds were detected in positive ion mode using the mass transition m/z 854.6-->286.2 and m/z 831.6-->263.2 for paclitaxel and the internal standard, respectively. The limit of quantitation for paclitaxel was 1 ng/ml with an imprecision of 5.2% following extraction of 0.1 ml of plasma. Linearity was confirmed over the whole calibration range (1-1000 ng/ml) with correlation coefficients higher than 0.99 indicating good fits of the regression models. The inter and intra-day precision was better than 9.5% and the accuracy ranged from 90.3 to 104.4%. The assay was simple, fast, specific and exhibited excellent ruggedness.     

Quantitative determination of sufentanil in human plasma by liquid chromatography-tandem mass spectrometry

A sensitive and specific method for the quantification of sufentanil in human plasma by liquid chromatography coupled with tandem mass spectrometry has been developed. Fentanyl was used as the internal standard. Rapid sample preparation involved purification on a C(18) solid-phase extraction column. Chromatographic separation of the analytes was obtained using an RP-C(18) mu-HPLC column. LC-MS-MS detection was performed by atmospheric pressure ionisation (API) source equipped with an ionspray (IS) interface operating in the positive ion mode. For unambiguous substance confirmation, three analyte precursor-product ion combinations were monitored during multiple reaction monitoring (MRM) LC-MS-MS analysis. The method's performance characteristics were evaluated in blank and spiked control plasma samples. Overall accuracy (relative error, R.E., %), repeatability (relative standard deviations, R.S.D., %) and within-laboratory reproducibility (R.S.D., %) ranged from -9.28 to -2.71%, from 6.42 to 2.82% and from 13.52 to 6.06%, respectively, for sufentanil. The limit of quantification for sufentanil in human plasma samples was 0.3 ng ml(-1). Due to its high sensitivity and specificity, the method was successfully employed for sufentanil determination in maternal plasma samples collected immediately before epidural administration of a single sufentanil dose to women in labour, 20 min after drug administration, and at birth in arterial and venous umbilical cord plasma samples from the newborn babies. Research is in progress to adopt the method for performance of complete pharmacokinetic studies of sufentanil in human plasma.     

An automatic 96-well solid phase extraction and liquid chromatography-tandem mass spectrometry method for the analysis of morphine, morphine-3-glucuronide and morphine-6-glucuronide in human plasma.

A bioanalytical method using automated sample transferring, automated solid phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS-MS) was developed for morphine (MOR), and its metabolites morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in human plasma. Samples of 0.25 ml were transferred into 96-well plate using automatic liquid handler (Multiprobe II). Automated SPE was carried out on a 96-channel programmable liquid handling workstation (Quadra 96) using a C(18) sorbent. The extract was injected onto a silica column using an aqueous-organic mobile phase. The chromatographic run time was 3.5 min per injection, with retention times of 1.5, 2.0 and 2.6 min for MOR, M6G, and M3G, respectively. The detection was by monitoring MOR at m/z 286-->152, M6G and M3G at m/z 462-->286. The deuterated internal standards were monitored at m/z 289-->152 for MOR-d(3), and m/z 465-->289 for M6G-d(3) and M3G-d(3). The standard curve range was 0.5-50 ng ml(-1) for MOR, 1.0-100 ng ml(-1) for M6G, and 10-1000 ng ml(-1) for M3G. The inter-day precision and accuracy of the quality control samples were <8% relative standard deviation (RSD) and <7% relative error (RE) for MOR, <5% RSD and <2% RE for M6G, and <2% RSD and <4% RE for M3G.     

Quantitative determination of methylnaltrexone in human serum using liquid chromatography-tandem mass spectrometry

Methylnaltrexone (MNTX) is a novel peripherally acting μ-opioid antagonist that prevents peripheral side effects of opioid drugs such as constipation without affecting the analgesia. We developed a selective and sensitive assay to measure MTNX concentrations in human serum.The drug was measured after protein precipitation with perchloric acid using naltrexone as internal standard and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for detection. The chromatography was performed isocratically on a RP18 column using 25 mM ammonium acetate buffer (pH 4)/acetonitrile (90%/10%; flow rate 200 μl/min) as mobile phase. The MS/MS analysis was performed in positive ionization mode monitoring the m/z transitions 356.4/284.2 for MNTX and 342.4/324.2 for naltrexone.The method was validated according to selectivity, linearity, accuracy, precision, recovery, matrix effects and stability. The validation range for MNTX in serum was 0.5-250 ng/ml. The developed LC-MS/MS was shown to be valid and successfully applied to measure serum-concentration-time curves of MNTX in a pilot study in healthy volunteers.     

Quantitative determination of rosuvastatin in human plasma by ion pair liquid-liquid extraction using liquid chromatography with electrospray ionization tandem mass spectrometry

A simple and sensitive liquid chromatography/tandem mass spectrometry method was developed and validated for the quantification of rosuvastatin in human plasma. After being treated with acetic acid and tetrabutyl ammonium hydroxide, the analyte was extracted by simple one-step liquid-liquid extraction with the internal standard (IS: estrone). The chromatographic separation was performed on a Phenomenex Luna C18 column with a mobile phase consisting of 2% formic acid/methanol (20:90, v/v) at a flow rate of 1.00 mL/min with a split of 200 microL to mass spectrometer. The retention time of rosuvastatin and internal standard was 2.3 and 3.4 min, respectively. Triple-quadrupole MS/MS detection was operated in positive mode by monitoring the transition of m/z 482-->258 for rosuvastatin and m/z 271-->253 for IS. Validation results indicated that the lower limit of quantification (LLOQ) was 0.1 ng mL(-1) and the assay exhibited a linear range of 0.1-20 ng mL(-1) and gave a correlation coefficient (r) of 0.9990 or better. Inaccuracy was less than 8.4% and imprecision less than 12.8% at all tested concentration levels. The analyte was stable in human plasma following three freeze/thaw cycles and for up to 8 weeks following storage at -20 degrees C. The assay was successfully applied to the analysis of rosuvastatin in human plasma samples derived from clinical pre-trials.     

HPLC-MS/MS法测定人体血浆中吲哒帕胺的浓度

目的:建立一种简便、灵敏的测定人体血浆中吲哒帕胺浓度的高效液相色谱-串联质谱(HPLC-MS/MS)方法。方法:以瑞格列奈钙为内标,采用乙腈:0.1%甲酸水溶液=90∶10为流动相,以Agilent-ZORBAX-C18柱(2.1mm×150mm,5.0m)色谱柱为分析柱,通过电喷雾离子源(ESI),以正离子多反应监测(MRM)方式进行进样检测。检测离子为[M+H]+m/z 364.1m/z 188.8(吲哒帕胺)和[M+H]+m/z 451.1m/z 134.8(瑞格列奈钙,内标)。结果:吲哒帕胺线性范围为0.5～50ng/mL,定量下限为0.5ng/mL,线性关系良好;高、中、低三个浓度的日内、日间的RSD均<15%,平均回收率为94.60%～110.33%。结论:本方法专属性强,操作简便,灵敏度高,适用于吲哒帕胺制剂的临床药动学研究。     

HPLC-MS-MS法定量测定人血浆中多潘立酮的浓度

目的：建立HPLC-MS-MS方法定量测定人血浆中多潘立酮浓度。方法：以地西泮为内标,采用甲醇：0.5%乙酸=80：20为流动相,以Inerstil C18（2.1mm×100mm,3.0μm）色谱柱为分析柱,通过电喷雾离子源（ESI）,以正离子多反应监测（MRM）方式进行检测。多潘立酮和地西泮用于定量分析的离子对分别为[M＋H]^＋m/z426.2→m/z175.2和[M＋H]^＋m/z285.0→m/z193.0。结果：多潘立酮线性范围为1～80μg·L-1,定量下限为1μg·^L-1（n=6）。日内、日间的RSD均〈15%,平均回收率〉75%。结论：本方法专属性强,样品处理方便,灵敏度高,适用于多潘立酮临床药动学研究。     

HPLC-MS/MS法测定人血浆中雷喏嗪的质量浓度

目的建立HPLC-MS/MS法测定人血浆中雷喏嗪的质量浓度。方法以伏立康唑为内标,采用乙腈-体积分数0.1%甲酸水溶液(90∶10)为流动相,以Agilent-ZORBAX-C18柱(150 mm×2.1 mm,5.0μm)色谱柱为分析柱,通过电喷雾离子源(ESI),以正离子多反应监测(MRM)方式进行检测。雷喏嗪和伏立康唑用于定量分析的离子对分别为[M+H]+m/z428.5→m/z279.3和[M+H]+m/z350.2→m/z281.3。结果雷喏嗪线性范围为20~5 000 ng·mL-1,定量下限为20 ng·mL-1。日内和日间的RSD均小于15%,平均回收率大于75%。结论该方法专属性强,样品处理方便,灵敏度高,适用于雷喏嗪的临床药动学研究。     

Quantitation of PGE9509924, a novel, nonfluorinated quinolone, in rat plasma using liquid chromatography electrospray-tandem mass spectrometry following solid-phase extraction sample clean-up in a 96-well format

PGE9509924, a novel nonfluorinated quinolone, is a potent antibacterial agent with a broad spectrum of activity. A semi-automated method using 96-well format, solid-phase extraction has been developed for quantitating PGE9509924 in rat plasma. The Waters Oasis HLB extraction plate containing a polymeric packing material was found to give the best overall recoveries. All liquid transfer steps other than aliquoting the plasma are accomplished using a 96-channel pipettor. Reverse-phase HPLC with electrospray/MS/MS detection using selective reaction monitoring is used to quantitate the samples. Stable isotopically labeled PGE9509924 is used as the internal standard. The assay is linear over the range from 0.01 to 10 ug/ml. Excellent precision is obtained within a single run and between multiple runs performed on different days. CVs of <6% were observed. The combination of the semi-automated, 96-well parallel sample processing and the short runtime on the LC/MS/MS results in a high throughput assay with reduced operator interaction.     

Determination of tiapride in human plasma using hydrophilic interaction liquid chromatography-tandem mass spectrometry

A rapid, sensitive and selective hydrophilic interaction liquid chromatography-tandem mass spectrometric (HILIC-MS/MS) method for the determination of tiapride in human plasma was developed. Tiapride and internal standard, metoclopramide were extracted from human plasma with dichloromethane at basic pH and analyzed on an Atlantis HILIC silica column with the mobile phase of acetonitrile-ammonium formate (190 mM, pH 3.0) (94:6, v/v). The analytes were detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r=0.999) over the concentration range of 1.00-200 ng/mL. The coefficient of variation and relative error for intra- and interassay at three QC levels were 6.4-8.8% and -2.0-3.6%, respectively. The recoveries of tiapride ranged from 96.3 to 97.4%, with that of metoclopramide (internal standard) being 94.2%. The lower limit of quantification for tiapride was 1.00 ng/mL using 100 microL of plasma sample.     

Determination of diethylstilbestrol in human plasma using high performance liquid chromatography-tandem mass spectrometry

A sensitive, fast, and reproducible high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of diethylstilbestrol in human plasma was developed and validated. The plasma samples were pretreated by direct deproteinization with ethyl acetate. Daidzein was used as the internal standard. The separation was carried out on a Agilent Technologies 1200 series XDB C₁₈ column (2.1 mm×150 mm, 5 µm) with a mobile phase of acetonitrile-2.5 mmol/L ammonium acetate (60:40, v/v). Triple quadrupole mass spectrometric detection in negative ion mode was used for multiple-reaction-monitoring of the transitions atm/z 267.2→237.3 and m/z 253.2→132.3 for diethylstilbestrol and daidzein, respectively.The calibration curves were linear over the concentration range from 0.1 to 20 ng/mL (r² = 0.9984). The lower limit of quantificationwas 0.1 ng/mL (s/n mLs)for diethylstilbestrol, which was sensitive enough to perform pharmacokinetic studies after diethylstilbestroladministration. Inter-day and intra-day precisions were no more than 7% with accuracies of 90%-105%. This method could be applied to therapeutic drug monitoring of diethylstilbestrol, which is helpful for evaluating the clinical efficacy and safety of diethylstilbestrol.     

A simple 96-well liquid-liquid extraction with a mixture of acetonitrile and methyl t-butyl ether for the determination of a drug in human plasma by high-performance liquid chromatography with tandem mass spectrometry

A simple 96-well plate liquid-liquid extraction (LLE), liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the determination of a basic drug candidate in human plasma. Against the wisdom of conventional approaches, an aqueous/organic miscible solvent, acetonitrile, was used for liquid-liquid extraction along with methyl t-butyl ether. The use of acetonitrile effectively eliminated the formation of the irregular emulsion between aqueous/organic interfaces and modulated the polarity of the extraction solvents to achieve the desired recovery. This approach, which solved the emulsion problem, permitted the method to be automated using standard 96-well plate technology. A practical application was demonstrated through the use of this technique in the measurement of a novel drug in human plasma samples by LC/MS/MS. Chromatographic separation was achieved isocratically on a Phenomenox C18(2) Luna column (2 mm x 50 mm, 5 microm). The mobile phase contained 60% of 0.1% formic acid and 40% acetonitrile. Detection was by positive ion electrospray tandem mass spectrometry. The standard curve, which ranged from 1.22 to 979ng/ml, was fitted to a 1/x2 weighted quadratic regression model. The validation results show that this method was very rugged and had excellent precision and accuracy. The actual sample analysis results further demonstrated that this extraction procedure is well suited for real life applications. It is expected that with some modifications, this approach can be applied for the extraction of similar compounds from various biological fluids.     

Simultaneous determination of sildenafil and its active metabolite UK-103,320 in human plasma using liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometric method for the simultaneous determination of sildenafil and its active N-demethylated metabolite, UK-103,320 in human plasma was developed. Sildenafil, UK-103,320 and the internal standard (DA-8159) were extracted from human plasma with dichloromethane at basic pH. A reverse-phase LC separation was performed on Luna phenylhexyl column with the mixture of acetonitrile-ammonium formate (10 mM, pH 6.0) (60:40, v/v) as mobile phase. The detection of analytes was performed using an electrospray ionization tandem mass spectrometry in the multiple reaction-monitoring mode. The lower limits of quantification for sildenafil and UK-103,320 were 2.0 ng/ml. The method showed a satisfactory sensitivity, precision, accuracy, recovery and selectivity.     

Quantitative assay of lorazepam and its metabolite glucuronide by reverse-phase liquid chromatography-tandem mass spectrometry in human plasma and urine samples

A LC/MS/MS method for the quantitative determination of lorazepam in human plasma and urine samples was developed and validated. The enantioselective assay allowed to separate the enantiomers and to verify the stereochemical instability of lorazepam. The linearity assessed for lorazepam unchanged was 0.2-20 ng of each enantiomer/ml plasma and 0.2-15 ng of each enantiomer/ml urine. The linearity assessed for total lorazepam (after enzymatic hydrolysis) was 1-30 ng of each enantiomer/ml plasma and 10-150 ng of each enantiomer/ml urine. The coefficients of variation obtained for the intra- and interassay precision were less than 15%. The method was applied to the investigation of the kinetic disposition and metabolism of racemic lorazepam administered as a single oral dose of 2 mg to a parturient. The occurrence of racemization required the calculation of the pharmacokinetic parameters as enantiomeric mixtures of lorazepam (t(1/2a) 3.5h; K(a) 0.198 ngh(-1); t(1/2) 11.5h; beta 0.060 h(-1); AUC(0-infinity) 192.1ngh/ml; CLt/f 2.41ml/minkg; Vd/f 173.5l; Fel 0.41%, and Cl(R) 0.0099 ml/minkg) and its metabolite lorazepam-glucuronide (t(1/2f) 1.2h; K(f) 0.578 h(-1); t(1/2) 16.6h; beta 0.042 h(-1); AUC(0-infinity) 207.6 ngh/ml; Fel 51.80%, and Cl(R) 98.32 ml/minkg). However, the determined confidence limits make the method suitable for application to clinical pharmacokinetic studies, even if the quantification of both the enantiomers is required.