A reliable, simple, and robust liquid chromatography-tandem mass spectro-metric (LC-MS/MS) method has been developed and validated that employs solid-phase extraction for the simultaneous estimation of amlodipine and valsartan in human K3EDTA plasma using amlodipine-d4 and valsartan-d9 as internal standards. Chromatographic separation of amlodipine and valsartan was achieved on the Luna C18 (2)100A (150 × 4.6 mm, 5 μm) column using acetonitrile: 5 mM ammonium formate solution (80:20, v/v) as the mobile phase at a flow rate of 0.8 mL/min in isocratic mode. Quantification was achieved using an electrospray ion interface operating in positive mode, under multiple reaction monitoring (MRM) conditions. The assay was found to be linear over the range of 0.302–20.725 ng/mL for amlodipine and 6.062–18060.792 ng/mL for valsartan. The method has shown good reproducibility, as intra- and interday precisions were within 10% and accuracies were within 8% of nominal values for both analytes. The method was successfully applied for the bioequivalence study of amlodipine and valsartan after oral administration of a fixed dose of the combination. Additionally, as required by the current regulatory bodies, incurred sample reanalysis was performed and found to be acceptable.

Background: Sensitive and selective analytical method is required for the estimation of lovastatin in human plasma as lovastatin has been reported to have high intra-subject variability and is converted to its active metabolite lovastatin hydroxy acid in in vitro system and vice versa. If this inter-conversion is not restricted, it could lead to pseudo estimation of lovastatin in human plasma. Methods: A specific, sensitive, and reproducible high-performance liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated for determination of lovastatin in human plasma, using lovastatin-d 3 as an internal standard. Lovastatin and lovastatin-d 3 were extracted from human plasma using solid phase extraction, separated on Luna C18 (2)100A (100 × 4.6 mm, 5 μm) column with mobile phase consisting of acetonitrile and 2 mM ammonium acetate buffer (pH 3.6) in the ratio of 90:10, v/v. Quantification was achieved by monitoring transitions of m/z 422.1 → 285.4 for lovastatin and 425.4 → 285.4 for lovastatin-d 3 in multiple reaction monitoring, using turbo ion source in positive polarity. Results: No matrix effect was observed within the linearity range of 0.121-35.637 ng/mL (r > 0.99). The degree of matrix effect for lovastatin was determined as 2.74 %, and it had no impact on incurred samples analysis with run time of 4.5 min. The intra-and inter-day precision values were within 11.38 and 8.62 % respectively, for lovastatin at the lower limit of quantification level. Conclusions: Stability data indicated that lovastatin is stable under various handling conditions and with insignificant inter-conversion between lovastatin and lovastatin hydroxy acid. The method was successfully applied for the bioequivalence study of lovastatin after oral administration of 40 mg tablet in healthy volunteer.