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A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for the determination of lamotrigine in human plasma using multiplexing technique (two HPLC units connected to one MS-MS). Lamotrigine was extracted from human plasma by solid-phase extraction technique using Oasis Hydrophilic Lipophilic Balance (HLB) or N-vinylpyrrolidone and divinylbenzene cartridge. A structural analog, 3,5-diamino-6-phenyl-1,2,4-triazine, was used as an internal standard (IS). A BetaBasic C(8) column was used for the chromatographic separation of analytes. The mass transition [M+H](+) ions used for detection were m/z 256.0 --> 211.0 for lamotrigine and m/z 188.0 --> 143.0 for IS. The method involved a simple multiplexing, rapid solid-phase extraction without evaporation and reconstitution. The proposed method has been validated for a linear range of 0.025 to 10.000 microg/mL with a correlation coefficient > or = 0.9991. The limit of quantification for lamotrigine was 0.025 microg/mL, and limit of detection was 50.000 pg/mL. The intra-run and inter-run precision and accuracy were within 10.0% for intra-HPLC runs and inter-HPLC runs. The overall recoveries for lamotrigine and IS were 97.9% and 92.5%, respectively. Total MS run time was 1.4 min per sample. The validated method has been successfully used to analyze human plasma samples for applications in pharmacokinetic, bioavailability, bioequivalence, or in vitro in vivo correlation studies.

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A rapid LC coupled with electrospray ionization (ESI) MS/MS method was developed and validated for the quantification of paroxetine in heparinized human plasma. The plasma samples were prepared by the solid-phase extraction method without drying or reconstitution. Elution was done with 0.5 mL 0.2% (v/v) formic acid in methanol-acetonitrile (65 + 35, v/v). The analyte and the internal standard (IS; imipramine hydrochloride) were chromatographed on a BDS Hypersil C18 column. The analyte was analyzed by LC/MS/MS with only 1.7 min run time. An ESI interface was chosen for ionization of the analyte from the sample matrix. Selected reaction monitoring mode for detection of paroxetine and the IS were achieved by using m/z 330.17/192.10 and 281.13/86.14, respectively. The LC retention times for paroxetine and imipramine were 0.94 and 1.05 min, respectively. The method was linear in the concentration range of 0.5-80.0 ng/mL with r > or = 0.9995. Recovery of paroxetine and imipramine ranged from 90 to 95%. The assay has been successfully applied to bioequivalence study samples for estimation of paroxetine in healthy human subjects.

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The plasma concentration profile of lamotrigine was predicted from the dissolution test data of the modified release 100 mg lamotrigine tablet by applying the in vitro-in vivo correlation (IVIVC). Three different release formulations (L-1, L-2 and L-3) and its profiles of in vitro data were generated in different dissolution media. Pharmacokinetics evaluation of these formulations was carried out in 12 healthy volunteers. In vitro-in vivo correlation was established from the generated dissolution and bioavailability data. A good correlation between the percentages dissolved vs absorbed (r2>0.989) was obtained using level A correlation. Evaluation of the internal predictability of level A correlation was calculated in terms of percent prediction error, which was found to be below 15%.

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A rapid LC-MS/MS method has been developed and validated for the determination of losartan (LOS) and its metabolite losartan acid (LA) (EXP-3174) in human plasma using multiplexing technique (two HPLC units connected to one MS/MS). LOS and LA were extracted from human plasma by SPE technique using Oasis HLB cartridge without evaporation and reconstitution steps. Hydroflumethiazide (HFTZ) was used as an internal standard (IS). The analytes were separated on Zorbax SB C-18 column. The mass transition [M-H] ions used for detection were m/z 421.0 --> 127.0 for LOS, m/z 435.0 --> 157.0 for LA, and m/z 330.0 --> 239.0 for HFTZ. The proposed method was validated over the concentration range of 2.5-2000 ng/mL for LOS and 5.0-3000 ng/mL for LA with correlation coefficient > or = 0.9993. The overall recoveries for LOS, LA, and IS were 96.53, 99.86, and 94.16%, respectively. Total MS run time was 2.0 min/sample. The validated method has been successfully used to analyze human plasma samples for applications in 100 mg fasted and fed pharmacokinetic studies.

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A selective, rapid and simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method is described for assay of donepezil in human plasma using escitalopram as an internal standard. Chromatographic separation was achieved on a Betabasic-C(8), 5 microm, 100 x 4.6 mm column using methanol:water:formic acid (90:9.97:0.03, v/v/v) as mobile phase. Detection of donepezil and internal standard was achieved by ESI MS/MS in positive ion mode using 380.20/91.10 and 325.13/262.00 transitions, respectively. The linearity over the concentration range of 0.15-50 ng/mL for donepezil was obtained and the lower limit of quantification was 0.15 ng/mL. For each level of quality control samples, inter-day and intra-day precisions (RSD) were < or =8.92 and 10.35% and accuracy (%RE) were < or =7.33% and 9.33%, respectively. The recovery was more than 88.50% for both donepezil and internal standard by solid-phase extraction, eliminating evaporation and reconstitution steps.

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A high throughput liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS) method is developed for the simultaneous estimation of clopidogrel (SR25990C) and its carboxylic acid metabolite (SR26334) in human plasma using glimepiride as internal standard. The extraction of SR25990C, its metabolite, and IS from the plasma (0.3 mL) involves treatment with phosphoric acid followed by solid-phase extraction (SPE). Sample preparation by this method yields clean extracts with quantitative and consistent mean recoveries of 98.05%, 85.45%, and 105.72% for SR25990C, SR26334, and IS, respectively. The SPE eluate without drying and reconstitution is analyzed by LC-MS-MS, operating in the positive ion and selective reaction monitoring mode. The injection volume is 2 microL with a total chromatographic run time of 5.0 min. The method response is linear over the dynamic range of 0.25 to 25.0 ng/mL for SR25990C and 50.0 to 6000.0 ng/mL for SR26334, with correlation coefficients of r > or = 0.9989 and 0.9984, respectively. The method is validated to demonstrate its specificity, linearity, accuracy, precision, recovery, matrix effect, dilution integrity, and stability studies. It is applied to study the bioavailability of 75 mg clopidogrel mesylate tablets in 16 human subjects with satisfactory results.

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The purpose of the present study was to examine the human oral absorption (HOA) predictability of the experimentally determined immobilized artificial membrane (IAM) chromatography capacity factor (log k'IAM) in conjunction with physicochemical descriptors. Transcellular permeation was modeled based on determination of log k'IAM considering pH partition hypothesis, and the independent variables were polar surface area (PSA) and molecular weight (MW). The correlation between log k'IAM determined at different pH and n-octanol/water partition coefficient (log P) and contribution of polarity (PSA) and size (MW) in the transcellular permeation model were the extension to the previous work. A data set of 37 compounds with partition coefficient values taken from the literature was employed to show importance of ionic interaction in oral absorption prediction. The highest log k'IAM value among screened pH 4.5, 5.5, 6.5 and 7.4 (log k'IAM4.5-7.4) in conjunction with PSA predicted HOA with coefficient of determination (CD) of 0.9001 compare to log k'IAM4.5-7.4 alone with CD of 0.8454 after excluding bretylium from the set of 28 structurally diverse drugs for known reason. PSA helped to avoid over estimation of HOA for amiloride, famotidine and furosemide. The model was tested for its applicability in drug development program and found to predict oral absorption using physically meaningful and structurally related properties making them relatively straightforward for a medicinal chemist to interpret.

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A new, rapid, and sensitive liquid chromatography-tandem mass spectrometry method is developed and validated to quantitate the sibutramine active metabolites mono desmethyl sibutramine (M1) and di-desmethyl sibutramine (M2) using imipramine as the internal standard in human plasma samples for routine bioequivalence studies. The method involves rapid solid-phase extraction from plasma, eliminating the drying and reconstitution steps. The analytes are chromatographed on a C8 reversed-phase chromatographic column and analyzed by mass spectrometry in the multiple reaction monitoring mode, which enables a quantitation limit at the sub-nanogram level. The method has a chromatographic run time of 2.8 min. The proposed method is validated with a linear range of 0.1-8.0 and 0.2-16.0 ng/mL for M1 and M2, respectively, with a correlation coefficient of regression > or = 0.9990. The method is sensitive and reproducible, having intra- and inter-assay precision at the lower limit of quantitation (0.1 ng/mL for M1 and 0.2 ng/mL for M2) < 10.0%. The overall recovery for M1 and M2 is 93.5% and 77.9%, respectively. The method has been applied to a bioequivalence clinical study with great success.

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A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the estimation of rivastigmine in human plasma. Rivastigmine was extracted from human plasma by using solid-phase extraction technique. Zolpidem was used as the internal standard. A Betabasic-8 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The mass transition ion-pair was followed as m/z 251.20-->206.10, 86.20 for rivastigmine and m/z 308.10-->235.10 for zolpidem. The method involves a rapid solid-phase extraction from plasma, simple isocratic chromatographic conditions and mass spectrometric detection that enables detection at sub-nanogram levels. The proposed method has been validated for a linear range of 0.2-20.0 ng/ml with a correlation coefficient > or =0.9988. The intra-run and inter-run precision and accuracy were within 10.0%. The overall recoveries for rivastigmine and zolpidem were 86.28% and 87.57%, respectively. The total run time was 2.0 min. The developed method was applied for the determination of the pharmacokinetic parameters of rivastigmine following a single oral administration of a 3 mg rivastigmine capsule in 20 healthy male volunteers.

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A high throughput and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the estimation of bisoprolol in human plasma using multiplexing technique (two HPLC units connected to one MS). Bisoprolol was extracted from human plasma using solid-phase extraction technique using metoprolol as internal standard. A Betabasic 8 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The mass transition ion-pair was followed as m/z 326.2-->116.1 for bisoprolol and m/z 268.2-->191.0 for metoprolol. The method involves a simple multiplexing, rapid solid-phase extraction, simple isocratic chromatography conditions and mass spectrometric detection which enable detection at sub-nanogram levels. The proposed method has been validated for a linear range of 0.5-70.0 ng/mL with correlation coefficient > or =0.9991. The precision and accuracy were within 10% for intra-HPLC runs and inter-HPLC runs. The overall recoveries for bisoprolol and metoprolol were 93.89% and 77.65%, respectively. Total MS run time was 0.90 min only. The developed method was applied for the determination of pharmacokinetic parameters of bisoprolol following a single oral administration of a 10mg bisoprolol tablet in 18 healthy male volunteers.

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A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the estimation of amlodipine in human plasma. Amlodipine was extracted from human plasma by using a solid-phase extraction technique. Imipramine was used as the internal standard. A Hypersil BDS C18 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The method involves a rapid solid-phase extraction from plasma, simple isocratic chromatography conditions and mass spectrometric detection that enables detection at sub-nanogram levels. The proposed method has been validated for a linear range of 0.1-10.0 ng/mL with correlation coefficient >or=0.9990. The intrarun and interrun precision and accuracy were within 10.0%. The overall recovery for amlodipine was 63.67%. Total run time was 3.2 min only.

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A high throughput liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the determination of valproic acid, an antiepileptic drug, in human plasma is described. It is a rapid and sensitive isocratic reversed-phase liquid chromatography-tandem mass spectrometric method equipped with turbo ion spray (TIS) source, operating in the negative ion and pseudo selective reaction monitoring (SRM) acquisition mode to quantify valproic acid. The extraction of valproic acid and hydrochlorothiazide (IS) from the plasma involved sample treatment with phosphoric acid followed by solid-phase extraction using Waters hydrophilic-lipophilic balance (HLB) cartridge giving extracts free from endogenous interferences. Sample preparation by this method yielded very good and consistent mean recoveries of 99.73 and 74.47% for valproic acid and IS, respectively. The method was linear over the dynamic range of 2.0-200.0mug/ml (covering entire therapeutic range) with a correlation coefficient r>/=0.9989. The coefficient of variance (CV, %) was 7.03% at 2.0mug/ml (LLOQ). This method was fully validated for its accuracy, precision, recovery and matrix effect especially because the pattern of elution of all the analytes may appear as flow injection type. The analyte stability was examined under conditions mimicking the sample storage, handling and analysis procedures. The method was successfully applied for bioequivalence studies in human subject samples after oral administration of 500mg formulations.

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A rapid, specific and sensitive LC-MS/MS assay using solid-phase extraction (SPE) for the determination of pravastatin, in human plasma is described. The plasma filtrate obtained after SPE, using a polymer base, a hydrophilic-lipophilic balance (HLB) cartridge, was submitted directly to short-column liquid chromatography-tandem mass spectrometric (LC-MS/MS) assay, with negligible matrix effect on the analysis. For validation of the method, the recovery of the free analytes was compared with that from an optimized extraction method, and the analyte stability was examined under conditions mimicking the sample storage, handling, and analysis procedures. The extraction procedure yielded extremely clean extracts with a recovery of 107.44 and 98.93% for pravastatin and IS, respectively. The intra-assay and inter-assay precisions for the samples at the LLOQ were 3.30 and 7.31% respectively. The calibration curves were linear for the dynamic range 0.5-200 ng/mL with correlation coefficient r > or = 0.9988. The intra- and inter-assay accuracy ranged from 95.87 to 112.40%. The method is simple and reliable with a total run time of 3 min. This novel validated method was applied to the pharmacokinetic (PK) study in human volunteers receiving a single oral dose of 40 mg immediate release (IR) formulation.

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Capacity factors are determined for a set of drugs for which human oral absorption (HOA) data are available, using immobilized artificial membrane (IAM) chromatography. The compound set represented acidic, basic, neutral and amphoteric drugs from various structure classes and having low to high human oral absorption. Effect of mobile phase pH on retention was investigated to determine the optimal condition for better correlation with HOA. The retention (capacity factor, k'(IAM) of each drug was measured by reverse phase HPLC using an IAM.PC.DD2 (1 cm x 3 mm i.d., 12 microm) column with an eluent of acetonitrile - 0.01 M phosphate buffer at pH 4.5-7.4. The pH dependent k'(IAM) was in accordance with pH partition theory. Using non-linear regression analysis the obtained log k'(IAM) values were compared with published data on HOA in order to establish correlation. The better correlation with HOA was observed when the highest log k'(IAM) value selected among pH 4.5-7.4 (R(2)=0.8566) for each drug rather than obtained at more traditional pH 7.4 (R(2)=0.7403). Finally, it was confirmed by Cook's D outlier test that there was no influential observation in the model that affect the relationship between IAM capacity factor and HOA. The assay conditions were optimized and validated to make it suitable for routine analysis and for compound characterization in early discovery where permeability may be an issue.

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A high-throughput and sensitive bioanalytical method using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) has been developed for the estimation of sibutramine and its two metabolites (M1 and M2). The extraction of sibutramine, its metabolites and imipramine (internal standard (IS)) from the plasma involved treatment with phosphoric acid followed by solid-phase extraction (SPE) using a hydrophilic-lipophilic balanced HLB cartridge. The SPE eluate without drying and reconstitution was analyzed by LC/MS/MS, equipped with a with turbo ion spray (TIS) source, operating in the positive and multiple reaction monitoring (MRM) acquisition mode. Sample preparation by this method yielded extremely clean extracts with quantitative and consistent mean recoveries; 95.12% for sibutramine, 92.74% for M1, 95.97% for M2 and 96.60% for the IS. The total chromatographic run time was 3.0 min with retention times of 2.51, 2.13, 2.09 min for sibutramine, M1, M2 and imipramine, respectively. The developed method was validated in human plasma matrix, with a sensitivity of 0.1 ng/mL (coefficient of variance (CV), 2.07%) for sibutramine, 0.1 ng/mL (CV, 3.59%) for M1 and 0.2 ng/mL (CV, 4.93%) for M2. Validation of the method for its accuracy, precision, recovery, matrix effect and stability was carried out especially with regard to real subject sample analysis. The response was linear over the dynamic range 0.1 to 8.0 ng/mL for sibutramine and M1, and 0.2 to 16.0 ng/mL for M2 with correlation coefficients of r > or = 0.9959 (sibutramine), 0.9935 (M1) and 0.9943 (M2). The method was successfully applied for bioequivalence studies in 40 human subjects with 15 mg capsule formulations.

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The first liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the determination of levetiracetam, an antiepileptic drug, in human plasma is described. The plasma filtrate obtained after solid-phase extraction (SPE), using a polymer-based, hydrophilic-lipophilic balanced (HLB) cartridge, was submitted directly to a short column LC/MS/MS assay. There was no significant matrix effect on the analysis. For validation of the method, the recovery of the free analytes was compared to that from an optimized extraction method, and the analyte stability was examined under conditions mimicking sample storage, handling, and analytical procedures. The extraction procedure yielded extremely clean extracts with a recovery of 79.95% and 89.02% for levetiracetam and the internal standard (IS), respectively. The intra-assay and inter-assay precision for the samples at the lower limit of quantitation (LLOQ) were 6.33 and 6.82%, respectively. The calibration curves were linear for the dynamic range of 0.5 to 50 microg/mL with a correlation coefficient r >/= 0.9971. The intra-assay accuracy at LLOQ, LQC, MQC, and HQC levels ranged from 81.60 to 95.40, 93.00 to 103.47, 95.97 to 104.09, and 91.15 to 95.18%, respectively, while the inter-assay accuracy at LLOQ, LQC, MQC and HQC levels varied from 80.20 to 95.40, 88.53 to 107.53, 95.97 to 108.45, and 91.15 to 112.70%, respectively. The method is rugged and fast with a total instrumental run time of 2 min. The method was successfully applied for bioequivalence studies in human subject samples after oral administration of 1000 mg immediate release (IR) formulations.

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A rapid and sensitive liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for the determination of isosorbide-5-mononitrate (5-ISMN), used in the treatment of angina pectoris, in human plasma is described. The quantification of 5-ISMN was performed via stable acetate adduct formation with a high relative abundance. The plasma filtrate obtained after solid-phase extraction (SPE), using a polymer based, hydrophilic-lipophilic balanced (HLB) cartridge, was submitted directly to reversed-phase high-performance liquid chromatography separation followed by ESI and detection of the resulting ions using triple-quadrupole mass spectrometry in selected reaction monitoring (SRM) mode. There was no significant matrix effect on the analysis. For validation of the method, the recovery of the free analyte response was compared to that obtained from an optimized extraction method. The analyte stability was examined under conditions mimicking the sample storage, handling, and analytical procedures. The extraction procedure yielded extremely clean extracts with a recovery of 95.51% and 93.98% for iossorbide-5-mononitrate and topiramate (internal standard (IS)), respectively. The calibration curves were linear for the dynamic range of 10.0 to 1000.0 ng/mL with a correlation coefficient r > or = 0.9985. The intra-assay and inter-assay precision for the samples at the lower limit of quantification (LLOQ) were 9.02 and 13.30%, respectively. The intra-assay accuracies at LLOQ, LQC, MQC and HQC levels varied from 98.13 to 118.15, 102.34 to 105.21, 100.69 to 109.68, and 95.76 to 102.92%, respectively, while the inter-assay accuracies ranged from 93.10 to 118.15, 93.03 to 107.04, 86.97 to 109.68 and 86.18 to 105.85%, respectively, at these levels. The method is rugged and fast with a total run time of 2 min. The method was successfully applied for a bioequivalence study in 24 human subject samples after oral administration of 60 mg extended release (ER) formulations.

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A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for simultaneous quantification of risperidone (RSP) and its active metabolite 9-hydroxyrisperidone (9-OH-RSP) in human plasma. The analytes were extracted from human plasma by using the protein precipitation extraction technique. Methyl risperidone was used as internal standard for RSP and 9-OH-RSP. A Betasil C18 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The mass transition ion-pair was followed as m/z 411.28 --> 191.15 for RSP and m/z 427.30 --> 207.10 for 9-OH-RSP. The method involves a simple extraction, isocratic chromatography conditions and mass spectrometric detection that enable detection at sub-nanogram levels. The proposed method has been validated with a linear range of 0.10-15.0 ng/mL for RSP and 9-OH-RSP. The intrarun and interrun precision and accuracy values were within 15%. The overall recoveries for RSP and 9-OH-RSP were 82.1% and 83.2%, respectively. The total analysis time was as low as 3.0 min only. The developed method was applied for the determination of the pharmacokinetic parameters of RSP and 9-OH-RSP following a single oral administration of a 1 mg RSP tablet in 24 healthy male volunteers.

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A high throughput bioanalytical method based on solid phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS), has been developed for the estimation of perindopril and its metabolite perindoprilat, an angiotensin-converting enzyme inhibitor in human plasma. Ramipril was used as internal standard (IS). The extraction of perindopril, perindoprilat and ramipril from the plasma involved treatment with phosphoric acid followed by solid phase extraction (SPE) using hydrophilic lipophilic balance HLB cartridge. The SPE eluate without drying were analyzed by LC-MS/MS, equipped with turbo ion spray (TIS) source, operating in the negative ion and selective reaction monitoring (SRM) acquisition mode to quantify perindopril and perindoprilat in human plasma. The total chromatographic run time was 1.5 min with retention time for perindopril, perindoprilat and ramipril at 0.33, 0.35 and 0.30 min. The developed method was validated in human plasma matrix, with a sensitivity of 0.5 ng/ml (CV, 7.67%) for perindopril and 0.3 ng/ml (CV, 4.94%) for perindoprilat. This method was extensively validated for its accuracy, precision, recovery, stability studies and matrix effect especially because the pattern of elution of all the analytes appears as flow injection elution. Sample preparation by this method yielded extremely clean extracts with very good and consistent mean recoveries; 78.29% for perindopril, 76.32% for perindoprilat and 77.72% for IS. The response of the LC-MS/MS method for perindopril and perindoprilat was linear over the range 0.5-350.0 ng/ml for perindopril and 0.3-40 ng/ml for perindoprilat with correlation coefficient, r>/=0.9998 and 0.9996, respectively. The method was successfully applied for bioequivalence studies in human subjects samples with 4 mg immediate release (IR) formulations.

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A highly precise and sensitive method for the estimation of indapamide in human whole blood using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) is described. The method developed is validated in human whole-blood matrix, with a sensitivity of 0.5 ng/ml as lower limit of quantification. The procedure for the extraction of indapamide and glimepiride as internal standard (IS) involves haemolysis and deprotienation of whole blood using ZnSO(4) followed by liquid-liquid extraction using ethyl acetate. The sample extracts after drying were reconstituted and analysed by LC-MS/MS, equipped with turbo ion spray (TIS) source, operating in the positive ion and selective reaction monitoring (SRM) acquisition mode to quantify indapamide in human whole blood. The mean recovery for indapamide was 82.40 and 93.23% for IS. The total run time was 2.5 min to monitor both indapamide and the IS. The response of the LC-MS/MS method for indapamide was linear over the range of 0.5-80.0 ng/ml with correlation coefficient, r>or=0.9991. The coefficient of variance (% CV) at 0.5 ng/ml was 4.02% and the accuracy was well within the accepted limit of +/-20% at 0.5 ng/ml and +/-15% at all other concentrations in the linear range. This method is fully validated for the accuracy, precision and stability studies and also applied to subject-sample analysis of bioequivalence study for 1.5mg sustained-release (SR) formulations.

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