LC-MS/MS法测定人血浆中的倍他米松17-丙酸酯及其药动学研究

目的:建立人血浆中倍他米松17-丙酸酯（B17P）的LC-MS/MS测定方法,并研究其在健康人体内的药动学特征。方法:采用Agilent Zorbax C18（2.1 mm×100 mm,3.5μm）色谱柱,以甲醇-水（88:12）为流动相,流速0.15 ml·min^-1;电喷雾（ESI）离子源,正离子电离模式,多反应离子监测（MRM）的扫描方式,B17P和二丙酸倍氯米松（内标,IS）的检测离子对分别选择为m/z 471.1→397.1和543.2→433.1。结果:B17P的线性范围为0.02～2.0 ng·ml^-1（r=0.999 3,n=5）,定量下限为0.02 ng·ml^-1,日内和日间精密度（RSD）均小于10.9%,提取回收率在70%左右,方法回收率均在94.5～106.6%范围内。B17P的t_1/2为（82.5±17.3）h,C_max为（0.73±0.18）h,AUC_0～1为（63.9±13.6）ng·h·ml^-1。结论:该法简便、快速、灵敏、准确,适用于B17P血药浓度测定及其人体药动学研究。     

Development and validation of an automated SPE-LC-MS/MS assay for valdecoxib and its hydroxylated metabolite in human plasma

A sensitive and specific liquid chromatography-tandem mass spectrometry assay was developed to quantitate valdecoxib (I) and its hydroxylated metabolite (II) in human plasma. The analytes (I and II) and a structurally analogue internal standard (IS) were extracted on a C(18) solid phase extraction (SPE) cartridge using a Zymark RapidTrace automation system. The chromatographic separation was performed on a narrow-bore reverse phase Zorbax XDB-C(8) HPLC column with a mobile phase of acetonitrile:water (50:50, v/v) containing 10 mM ammonium acetate. The analytes were ionized using negative electrospray mass spectrometry, then detected by multiple reaction monitoring (MRM) with a tandem mass spectrometer. The precursor to product ion transitions of m/z 313-->118 and m/z 329-->196 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 0.5-200 ng/ml of I and II in human plasma with absolute recoveries from plasma at 91 and 86%, respectively. The lower limit of quantitation was 0.5 ng/ml for I and II. Acceptable precision and accuracy were obtained for concentrations over the calibration curve ranges (0.5-200 ng/ml). Sample analysis time for each injection was 5 min, a throughput of 70 human plasma standards and samples per run was achieved. The assay has been successfully used to analyze human plasma samples to support clinical phase I and II studies.     

High performance liquid chromatography-tandem mass spectrometric determination of rupatadine in human plasma and its pharmacokinetics

A simple, rapid, sensitive and selective liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method was developed and validated for the quantification of rupatadine in human plasma using estazolam as internal standard (IS). Following liquid-liquid extraction, the analytes were separated using a mobile phase of methanol-ammonium acetate (pH 2.2; 5mM) (50:50, v/v) on a reverse phase C18 column and analyzed by a triple-quadrupole mass spectrometer in the positive ion and multiple reaction monitoring (MRM) mode, m/z 416-->309 for rupatadine and m/z 295-->267 for the IS. The assay exhibited a linear dynamic range of 0.1-100 ng/ml for rupatadine in human plasma. The lower limit of quantification (LLOQ) was 0.1 ng/ml with a relative standard deviation of less than 20%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The validated LC-MS/MS method has been successfully applied to study the pharmacokinetics of rupatadine in healthy volunteers.     

Simultaneous determination of clozapine and its N-desmethyl and N-oxide metabolites in plasma by liquid chromatography/electrospray tandem mass spectrometry and its application to plasma level monitoring in schizophrenic patients

A liquid chromatography tandem mass spectrometry (LC-MS-MS) assay method for the simultaneous determination of clozapine and its N-desmethyl (norclozapine) and N-oxide metabolites in human plasma is described. The compounds were extracted from plasma by a single step liquid-liquid extraction procedure and analyzed using a high performance liquid chromatography electrospray tandem mass spectrometer system. The compounds were eluted isocratically on a C-18 column, ionized using positive ion atmospheric pressure electrospray ionization method by a TurboIonspray source and analyzed using multiple reaction monitoring mode. The ion transitions monitored were m/z 327 --> m/z 270 for clozapine, m/z 313 --> m/z 192 for norclozapine, m/z 343 --> m/z 256 for clozapine-N-oxide and m/z 421--> m/z 201 for internal standard. The standard curves of clozapine, norclozapine and clozapine-N-oxide were linear over the range of 1 ng/ml to 1000 ng/ml when 0.5 ml of plasma was used for the analysis (r(2) >0.998). Three pooled plasma samples collected from patients who were treated with clozapine were used as long-term quality control samples to check the validity of spiked standard curve samples made at various times. The intra- and inter-assay variations for the spiked standard curve and quality control samples were less than 14%. These variations for the long-term patient quality control samples were less than 11%. The LC-MS-MS assay for simultaneous determination of clozapine, norclozapine and clozapine-N-oxide reported here is highly specific, sensitive, accurate and rapid. This method is currently being used for the plasma level monitoring of clozapine and its N-desmethyl and N-oxide metabolites in patients treated with clozapine. The plasma levels of clozapine, norclozapine and clozapine-N-oxide varied widely within and among patients. The data revealed that the norclozapine and clozapine N-oxide metabolites were present at about 58%+/-14% and 17%+/-6% of clozapine concentrations in plasma, respectively.     

LC-MS-MS determination of exemestane in human plasma with heated nebulizer interface following solid-phase extraction in the 96 well plate format

A sensitive, specific and rapid analytical method for the quantitation of exemestane (EXE) in human plasma has been developed. EXE, 6-methylen-androsta-1,4-diene-3,17-dione, is an orally active irreversible steroidal aromatase inhibitor used for the therapy of metastatic postmenopausal breast cancer, with estrogen-dependent pathological conditions. The method involves extraction of EXE from human plasma by solid phase extraction using C2 endcapped sorbent in the 96 well plate format (50 mg/2 ml). After conditioning of the sorbent with 1 ml of acetonitrile (x2) the plates were rinsed with 1 ml of water (x2). The prepared samples (0.5 ml plasma, spiked with [13C3] EXE as internal standard (IS) and diluted with 0.5 ml water) were loaded and drawn through the plate with a minimum of vacuum. The plates were then washed with 1 ml acetonitrile:water (10:90) followed by a drying step for 30 min at full vacuum. Elution was by 0.15 ml of 0.1% trifluoracetic acid in acetonitrile (x2) under a minimum of vacuum. Aliquots of 80 microl were finally injected into the LC-MS-MS system. A Zorbax SB C8 column (4.6 x 150 mm, 5 microm) was used to perform the chromatographic separation; the mobile phase was 100% acetonitrile. MS detection used the heated nebulizer interface, with multiple reaction monitoring (MRM) (297-->121 m/z for EXE and 300-->123 m/z for IS) operated in positive ion mode. A weighed linear regression analysis (weighing factor 1/x2) was used to calculate EXE concentration in standard and unknown samples. The method was fully validated in the concentration range 0.05-25 ng ml(-1).     

A validated SPE-LC-MS/MS assay for Eplerenone and its hydrolyzed metabolite in human urine

An automated LC-MS/MS assay was validated to quantitate the first selective aldosterone blocker Eplerenone (I) and its hydrolyzed metabolite (II) in human urine. After the addition of the stable isotope labeled internal standards, human urine samples were extracted on a C(18) solid phase extraction (SPE) cartridge using a Zymark RapidTrace automation system. The extraction eluates were diluted with 20 mM ammonium acetate aqueous solution and directly injected onto the LC-MS/MS system. The chromatographic separation was performed on a reverse phase Zorbax XDB-C(8) HPLC column (2.1 x 50 mm, 5 microm) with a mobile phase of acetonitrile:water (40:60, v/v) containing 10 mM ammonium acetate (pH 7.4). I and II were ionized using positive and negative ionization mass spectrometry, respectively, to achieve the best sensitivity. The ionization polarity was switched during the run at approximately 2.5 min after the injection. Multiple reaction monitoring (MRM) with a tandem mass spectrometer was used to detect the analytes. The precursor to product ion transitions of m/z 415-->163 and m/z 431-->337 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 50-10000 ng/ml of urine for both of I and II. The lower limit of quantitation (LLOQ) was 50 ng/ml for I and II. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. Sample analysis time for each injection was 5 min; a throughput of 100 human urine standards and samples per run was achieved.     

Liquid chromatography/tandem mass spectrometry for the determination of carbamazepine and its main metabolite in rat plasma utilizing an automated blood sampling system

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the simultaneous determination of carbamazepine and its main metabolite carbamazepine 10,11-epoxide in rat plasma is described. The method consists of a liquid-liquid extraction procedure and electrospray LC/MS/MS analysis. The chromatographic separation was achieved within 5 min using a C(8) (150 mm x 2.1mm) 5 microm column with a mobile phase composed of water/acetonitrile/acetic acid (69.5:30:0.5, v/v/v) at a flow rate of 0.4 ml/min. D(10)-carbamazepine is used as the internal standard for all compounds. Analytes were determined by electrospray ionization tandem mass spectrometry in the positive ion mode using selected reaction monitoring (SRM). Carbamazepine was monitored by scanning m/z 237-->194, carbamazepine 10,11-epoxide by m/z 253-->210 and d(10)-carbamazepine by m/z 247-->204. The lower limit of quantitation (LLOQ) is 5 ng/ml for each analyte, based on 0.1 ml aliquots of rat plasma. The extraction recovery of analytes from rat plasma was over 87%. Intra-day and inter-day assay coefficients of variations were in the range of 2.6-9.5 and 4.0-9.6%, respectively. Linearity is observed over the range of 5-2000 ng/ml. This method was used for pharmacokinetic studies of carbamazepine and carbamazepine 10,11-epoxide in response to two different blood sampling techniques (i.e., manual sampling versus automated sampling) in the rat. Several differences between the two sampling techniques suggest that the method of blood collection needs to be considered in the evaluation of pharmacokinetic data.     

Sensitive LC-MS/MS methods for the quantification of RGH-188 and its active metabolites, desmethyl- and didesmethyl-RGH-188 in human plasma and urine

Selective and sensitive LC-MS/MS methods have been developed and validated for simultaneous determination of RGH-188, a novel atypical antipsychotic, and its two active metabolites, desmethyl- and didesmethyl-RGH-188 in human plasma and urine. Deuterated analytes, [2H6]-RGH-188, [2H3]-desmethyl-RGH-188 and [2H8]-didesmethyl-RGH-188 were used as internal standards (IS). The compounds were isolated from the alkalized biological matrix using liquid-liquid extraction (LLE) and the extracts were analysed by reversed-phase HPLC with MS/MS detection. The chromatographic run time was 5.0min per injection. The PE Sciex API 365 mass spectrometer was equipped with a TurboIonSpray interface and operated in positive-ion, multiple reaction monitoring (MRM) mode. The mass transitions monitored were m/z 427.3-->382.2, 413.2-->382.2, 399.2-->382.2, 433.3-->382.2, 416.2-->382.2 and 407.3-->390.2 for RGH-188, desmethyl-RGH-188, didesmethyl-RGH-188, [2H6]-RGH-188, [2H3]-desmethyl-RGH-188 and [2H8]-didesmethyl-RGH-188, respectively. The lower limit of quantification (LLOQ) was 0.05 and 0.1ng/ml for RGH-188 and its metabolites, respectively, using 1ml of plasma. LLOQ in 1ml of urine was 0.1ng/ml for all three analytes. The methods were validated for selectivity, linearity, accuracy and precision. The lower limit of quantification, dilution integrity, matrix effect, stability of the analytes in the biological matrix during short- and long-term storage and after three freeze-thaw cycles were also tested. The assays were simple, specific and robust enough to support clinical development of RGH-188.     

Determination of cetirizine in human plasma using high performance liquid chromatography coupled with tandem mass spectrometric detection: application to a bioequivalence study

A rapid, sensitive and selective HPLC-MS/ MS method was developed and validated for the quantification of cetirizine dihydrochloride (CAS 83881-51-0) in human plasma using mosapride citrate as internal standard (IS, CAS 112885-42-4). Following liquid-liquid extraction, the analytes were separated using a mobile phase consisting of methanol and aqueous ammonium acetate solution (10 mM) (60:40, v/v) on a reverse phase C18 column and analyzed by a triple-quadrupole mass spectrometer in the selected reaction monitoring (SRM) mode using the respective [M+H]+ ions, m/z 398 --> 201 for cetirizine and m/z 422 --> 198 for mosapride. The analysis time for each run was 8.0 min. The assay exhibited a linear dynamic range of 0.5-500 ng/ml for cetirizine dihydrochloride in human plasma. The lower limit of quantification (LLOQ) was 0.5 ng/ml with a relative standard deviation of less than 15% (all the concentration data in this study related to the salt (cetirizine dihydrochloride)). Acceptable precision and accuracy were obtained for concentrations over the standard curve range. It is the first time that the validated HPLC-MS/MS method has been successfully applied to a bioequivalence study in 20 healthy male Chinese volunteers.     

Pharmacokinetic characterization of a novel α7 nicotinic acetylcholine receptor (nAChR) positive allosteric modulator LD486 in rat plasma using a validated LC-MS/MS assay

The deficiency of neuronal α7-nicotinic acetylcholine receptor (α7 nAChR) channel is implicated in cognition deficit and neuropsychiatric disorders. Chemical activation of α7 nAChR improves learning, memory, and sensory gating in animal models. To identify novel α7 nAChR activators, we recently identified a lead compound LD486 that as a positive allosteric modulator (PAM) selectively activates α7 nAChR. In this study we developed a simple, reliable and efficient assay of high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) and analyzed the pharmacokinetics of this novel LD486 in rat plasma. Separation of compound LD486 from plasma was achieved using a reversed-phase C₁₈ column with a mobile phase of 0.1% formic acid in H₂O (80:20, v:v), using compound A1223 as an internal standard (IS) with a flow rate of 0.5 mL/min. The quantitative analysis was performed using multiple reaction monitoring (MRM) at the specific ion transition of m/z 419.0 [M+H]⁺→m/z 169.0 for LD486 and m/z 400.0 [M+H]⁺→m/z 129.9 for A1223 in the positive ion mode with electrospray ionization (ESI) source. This validated LC-MS/MS method shows good linearity over the range 4–4000 ng/mL with the lowest limit of quantitation (LLOQ) at 4 ng/mL as well as satisfied intra- and inter-day precision, accuracy, extraction recovery and matrix effect.The stability testing indicates that LD486 in rat blood is stable under three freeze-thaw cycles, in room temperature at 22 ^oC for 2 h and 12 h, and for 2 weeks at −20 ^oC. This developed method was successfully applied to the pharmacokinetic analysis of intravenous (1 mg/kg) and oral (3 mg/kg and 30 mg/kg) administration of LD486 in SD rats.     

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of tenofovir and emtricitabine in human plasma and its application to a bioequivalence study

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for simultaneous quantification of Tenofovir (TEN) and Emtricitabine (EMT) in human plasma using Chromolith Speed Rod RP18. The mass transition ion-pair has been followed as m/z 288.10-->176.10 for TEN, m/z 248.20-->130.20 for EMT and m/z 230.10-->112.10 for Lamivudine (LAM). The method involves solid phase extraction from plasma, simple isocratic chromatographic conditions and mass spectrometric detection using an API 5000 instrument that enables detection at nanogram levels. Lamivudine was used as the internal standard. The proposed method has been validated with a linear range of 10-600 ng/ml for TEN and 25-2,500 ng/ml for EMT. The intrarun and interrun precision values are within 12.0% for TEN and 15.6% for EMT at their respective LOQ levels. The overall recoveries for TEN and EMT were 84.3% and 68.5%, respectively. Total elution time was as low as 2 min.     

用UPLC-MS/MS法测定肝功能不全患者血浆中伏立康唑的浓度

目的 建立超高效液相色谱-串联质谱(UPLC-MS/MS)方法以测定人血浆中伏立康唑的浓度,用于临床治疗药物监测.方法 血浆中加入甲醇进行蛋白沉淀,取上清液用于UPLC-MS/MS分析.分析柱为InertSustain C18 HP(3.0 mm×100 mm,3μm),流动相为水-乙腈(15:85)等度洗脱,流速0....     

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.     

A sensitive LC/MS/MS method using silica column and aqueous-organic mobile phase for the analysis of loratadine and descarboethoxy-loratadine in human plasma

A sensitive method using liquid chromatography with tandem mass spectrometric detection (LC/MS/MS) was developed and validated for the simultaneous analysis of antihistamine drug loratadine (LOR) and its active metabolite descarboethoxy-loratadine (DCL) in human plasma. Deuterated analytes, i.e. LOR-d(3) and DCL-d(3) were used as the internal standards (I.S.). Analytes were extracted from alkalized human plasma by liquid/liquid extraction using hexane. The extract was evaporated to dryness under nitrogen, reconstituted with 0.1% (v/v) of trifluoroacetic acid (TFA) in acetonitrile, and injected onto a 50 x 3.0 mm I.D. 5 microm, silica column with an aqueous-organic mobile phase consisted of acetonitrile, water, and TFA (90:10:0.1, v/v/v). The chromatographic run time was 3.0 min per injection and flow rate was 0.5 ml/min. The retention time was 1.2 and 2.0 min for LOR and DCL, respectively. The tandem mass spectrometric detection was by monitoring singly charged precursor-->product ion transitions: 383-->337 (m/z) for LOR, 311-->259 (m/z) for DCL, 388-->342 (m/z) for LOR-d(3), and 316-->262 (m/z) for DCL-d(3). The low limit of quantitation (LLOQ) was 10 pg/ml for LOR and 25 pg/ml for DCL. The inter-day precision of the quality control (QC) samples was 3.5-9.4% relative standard deviation (R.S.D.). The inter-day accuracy of the QC samples was 99.0-107.9% of the nominal values.     

LC-MS/MS法同时检测人血浆中氟尿嘧啶、尿嘧啶和二氢尿嘧啶的浓度及其临床应用

目的:建立同时测定人血浆中氟尿嘧啶、尿嘧啶和二氢尿嘧啶浓度的方法 ,并应用于临床.方法:建立LC-MS/MS法,以溴尿嘧啶为内标,采用Waters Atlantis T3色谱柱(100 mm×3.0 mm,3μm);0.1％ 甲酸水溶液(V:V,A相)-甲醇(B相)为流动相,梯度洗脱(0～2 min,5％B;2.0～2...     

Determination of morphine, morphine-3-glucuronide and morphine-6-glucuronide in monkey and dog plasma by high-performance liquid chromatography-electrospray ionization tandem mass spectrometry

A specific and simultaneous assay of morphine, morphine-3-glucuronide (M-3-G) and morphine-6-glucuronide (M-6-G) in monkey and dog plasma has been developed. These methods are based on rapid isolation using solid phase extraction cartridge, and high-performance liquid chromatography (HPLC)-electrospray ionization (ESI)-tandem mass spectrometric (MSMS) detection. Analytes were separated on a semi-micro ODS column in acetonitrile-formic (or acetic) acid mixed solution. The selected reaction monitoring for assay in monkey and dog plasma, as precursor-->product ion combinations of m/z 286-->286 for morphine, m/z 462-->286 for glucuronides and m/z 312-->312 for internal standard (IS, nalorphine) were used. The linearity of morphine, M-3-G and M-6-G was confirmed in the concentration range of 0.5-50, 25-2500, 2.5-250 ng/ml in monkey plasma, 0.5-100, 25-5000, 2.5-500 ng/ml in dog plasma, respectively. The precision of this assay method, expressed as CV, was less than 15% over the entire concentration range with adequate assay accuracy. Therefore, the HPLC-ESI-MSMS method is useful for the determination of morphine, M-3-G and M-6-G with sufficient sensitivity and specificity in pharmacokinetic studies.     

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.     

LC/MS/MS法测定血浆中左羟丙哌嗪浓度及其药代动力学

目的建立测定血浆中左羟丙哌嗪的液相色谱-串联质谱法，考察左羟丙哌嗪在中国健康志愿者体内的药代动力学行为。方法血浆样品经液-液提取后，进行色谱分离，在三重四极杆串联质谱仪上，以多重反应离子监测(MRM)方式进行定量分析，用于监测的离子为m/z 237 → m/z 120（左羟丙哌嗪）和m/z 288 → m/z 58(佐米曲普坦，内标)。结果左羟丙哌嗪的最低定量浓度为0.25 μg·L^-1，线性范围为0.25-500.0 μg·L^-1，精密度与准确度符合生物样品分析要求。结论该法操作简便、快速、灵敏度高。可检测出健康志愿者po左羟丙哌嗪60 mg,其24 h后的血药浓度，适于临床药代动力学研究。     

Quantification of levetiracetam in human plasma by liquid chromatography-tandem mass spectrometry: application to therapeutic drug monitoring

A rapid, selective, reliable, precise, accurate, and reproducible tandem mass spectrometric (MS-MS) method for the quantification of levetiracetam (LEV) in human plasma using adenosine as an internal standard (IS) has been developed and validated. The drug and IS were extracted by solid phase extraction (SPE) technique and analyzed on Symmetry((R)) C(18) column (5 microm, 3.9 mm x 50 mm) using a mobile phase of methanol-water-formic acid (97:03:0.25, v/v/v) at a flow rate of 0.2 ml/min. Quantitation was achieved using a positive electrospray ionization (ESI+) interface employing multiple reaction monitoring (MRM) mode at MRM transitions m/z 171>126 and m/z 268>136 for LEV and IS, respectively. The method was validated over the concentration range of 1.0-40 microg/ml (r>0.99) with a limit of quantification of 1.0 microg/ml (R.S.D.%; 4.1 and Bias%; -9.0 to + 11.0%). Intra- and inter-run precision of LEV assay at three concentrations ranged from 0.6 to 8.9% with accuracy (bias) varied from -4.0 to 8.6% indicating good precision and accuracy. Analytical recoveries of LEV and IS from spiked human plasma were in the range of 91.7-93.4% and 80.2-84.1%, respectively. Stability of LEV in human plasma samples at different conditions showed that the drug was stable under the studied conditions. Matrix effect study showed a lack of matrix effect on mass ions of LEV and IS. The described method compared well with the commercial HPLC-UV method of Chromsystem (r(2)=0.99). The suitability of the developed method for therapeutic drug monitoring was demonstrated by measuring LEV in human plasma samples of epileptic patients treated with LEV.