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A sensitive, selective and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of bupropion (BUP) and its major active metabolite hydroxybupropion (HBUP) in human plasma. Separation of both the analytes and venlafaxine as internal standard (IS) from 50 μL human plasma was carried out by solid-phase extraction. The chromatographic separation of the analytes was achieved on a Zorbax Eclipse XDB C(18) (150 × 4.6 mm, 5 µm) analytical column using isocratic mobile phase consisting of 20 mm ammonium acetate-methanol (10:90, v/v), with a resolution factor of 3.5. The method was validated over a wide dynamic concentration range of 0.1-350 ng/mL for BUP and 0.1-600 ng/mL for HBUP. The matrix effect was assessed by post-column infusion and the mean process efficiency was 96.08 and 94.40% for BUP and HBUP, respectively. The method was successfully applied to a bioequivalence study of 150 mg BUP (test and reference) extended release tablet formulation in 12 healthy Indian male subjects under fed conditions.

A sensitive and selective method has been proposed for the simultaneous determination of amlodipine (AML), valsartan (VAL) and hydrochlorothiazide (HCTZ) in human plasma by liquid chromatography–tandem mass spectrometry (LC–MS/MS). The analytes and their deuterated analogs were quantitatively extracted from 100 µL human plasma by solid phase extraction on Oasis HLB cartridges. The chromatographic separation of the analytes was achieved on a Chromolith RP18e (100 mm × 4.6 mm) analytical column within 2.5 min. The resolution factor between AML and VAL, AML and HCTZ, and VAL and HCTZ was 2.9, 1.5 and 1.4, respectively, under isocratic conditions. The method was validated over a dynamic concentration range of 0.02–20.0 ng/mL for AML, 5.00–10,000 ng/mL for VAL and 0.20–200 ng/mL for HCTZ. Ion-suppression/enhancement effects were investigated by post-column infusion technique. The mean IS-normalized matrix factors for AML, VAL and HCTZ were 0.992, 0.994 and 0.998, respectively. The intra-batch and inter-batch precision (% CV) across quality control levels was ≤ 5.56% and the recovery was in the range of 93.4%–99.6% for all the analytes. The method was successfully applied to a bioequivalence study of 5 mg AML + 160 mg VAL + 12.5 mg HCTZ tablet formulation (test and reference) in 18 healthy Indian males under fasting. The mean log-transformed ratios of Cmax, AUC0–120h and AUC0-inf and their 90% CIs were within 90.2%–102.1%. The assay reproducibility was demonstrated by reanalysis of 90 incurred samples.

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