Validated LC-ESI-MS/MS method for simultaneous quantitation of felodipine and metoprolol in rat plasma: application to a pharmacokinetic study in rats.

A highly sensitive and specific LC-ESI-MS/MS method has been developed and validated for simultaneous quantification of felodipine (FDP) and metoprolol (MPL) in rat plasma (50 μL) using phenacetin as an internal standard (IS) as per the FDA guidelines. Liquid-liquid extraction method was used to extract the analytes and IS from rat plasma. The chromatographic resolution of FDP, MPL and IS was achieved with a mobile phase consisting of 0.2% formic acid in water-acetonitrile (25:75, v/v) with a time program flow gradient on a C18 column. The total chromatographic run time was 4.0 min and the elution of FDP, MPL and IS occurred at 1.05, 2.59 and 1.65 min, respectively. A linear response function was established for the range of concentrations 0.59-1148 and 0.53-991 ng/mL for FDP and MPL, respectively, in rat plasma. The intra- and inter-day accuracy and precision values for FDP and MPL met the acceptance as per FDA guidelines. FDP and MPL were stable in battery of stability studies viz., bench-top, auto-sampler and freeze-thaw cycles. The validated assay was applied to a pharmacokinetic study in rats.