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No information on the pharmacokinetic characteristics of amlodipine (AML) metabolites is available. This study aimed to develop a method based on isocratic liquid chromatography coupled to tandem mass spectrometry for the simultaneous determination of AML and its 2 major metabolites, dehydroamlodipine (DH-AML) and O-des[2-aminoethyl]-O-carboxymethyl DH-AML (CM-DH-AML), and to use it for monitoring this drug in hypertensive patients.Acetonitrile-deproteinized plasma specimens were separated using an octadecyl-silica column (3-μm particle size) with a mobile phase consisting of 50% methanol containing 0.15% of formic acid in water. The run time was 9 minutes. The mass spectrometer was run in the positive ion electrospray ionization mode. This method was applied for the determination of AML and its metabolites in plasma samples from patients treated with this drug.The calibration curves in human plasma of AML, DH-AML, and CM-DH-AML were linear over the concentration ranges of 0.5–64, 1–64, and 0.5–64 ng/mL, respectively, and their lower limits of quantification were 0.5, 1, and 0.5 ng/mL, respectively. Their extraction recovery rates and matrix factors in human plasma were 94.8%–109.0% and 97.0%–101.4%, respectively. The intra-assay and interassay imprecisions and accuracies were within 10.8% and 95.4%–111.2%, respectively. The plasma concentration ranges of AML, DH-AML, and CM-DH-AML were 6.5–20.9, 1.4–10.9, and 5.6–38.3 ng/mL, respectively.The present method with acceptable analytical performance can be helpful for monitoring the plasma concentration of AML, including the determination of its metabolites in patients with hypertension.