An analytical method based on liquid-liquid extraction has been developed and validated for analysis of agomelatine in human plasma. Fluoxetine was used as an internal standard for agomelatine. A Betasil C18 (4.0 × 100 mm, 5 µm) column provided chromatographic separation of analytes followed by detection with mass spectrometry. The method involves simple isocratic chromatographic conditions and mass spectrometric detection in the positive ionization mode using an API-4000 system. The proposed method has been validated with linear range of 0.050-8.000 ng/ml for agomelatine. The intra-run and inter-run precision values are within 12.12% and 9.01%, respectively, for agomelatine at the lower limit of quantification level. The overall recovery for agomelatine and fluoxetine was 67.10% and 72.96%, respectively. This validated method was used successfully for analysis of plasma samples from a pharmacokinetic study.

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A rapid and sensitive LC-MS-MS method for the determination of alverine (ALV) and its major metabolite, monohydroxy alverine (MHA), in human plasma using imipramine as an internal standard was developed and validated. The analytes were extracted from 0.5 mL aliquots of human plasma by solid phase extraction, using oasis cartridge. Chromatographic separation was carried on Thermo Gold C18 column (50 × 4.6 mm, 5 μ) at 30 °C, with isocratic mobile phase, a flow rate of 0.4 mL/min and a total run time of 3.5 min. Detection and quantification were performed using a mass spectrometer in the selected reaction-monitoring mode with positive electrospray ionization atm/z282.3 → 91.11 for alverine,m/z298.3 → 106.9 for mono-hydroxy-alverine, andm/z281.0 → 86.0 for internal standard (IS) respectively. This assay was linear over a concentration range of 0.060-10 ng/mL with a lower limit of quantification of 0.060 ng/mL for both alverine and monohydroxy alverine. The coefficient of variation for the assay precision were <9.18% and <8.44%, the accuracy were >104.66% and >100.38% for alverine and monohydroxy alverine respectively. This method was successfully applied to a pharmacokinetic study after oral administration of alverine citrate 60 mg capsule in healthy male subjects.

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