Determination of Amlodipine in Human Plasma by LC-MS/MS and Its Bioequivalence Study in Healthy Chinese Subjects

A sensitive and reproducible liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of amlodipine in human plasma, with gliclazide as an internal standard (IS). The analyte was extracted with ethyl acetate and analyzed on a Diamond C18 (150 mm× 4.6 mm, 5 μm) column. The mobile phase was composed of methanol ?10 mM ammonium acetate with gradient flow rates and gradient conditions. Amlodipine and IS were ionized by positive ion pneumatically assisted electrospray and detected in the multi-reaction monitoring (MRM) mode using precursor→productions of m/z 409.2→238.1, 294.1 and m/z 324.2→127.3, respectively. The specificity, matrix effect, recovery, sensitivity, linearity, accuracy, precision, and stabilities were all validated over the concentration range of 0.05 - 12 ng/mL. The 90% confidence interval (CI) for AUC0-t, AUC0-∞ and Cmax ratios (test: reference) were all within 80% - 125% interval proposed by FDA. It is concluded that the validated method can successfully fulfill the requirement of clinical bioequivalence study of amlodipine in healthy Chinese subjects after administration of amlodipine/losartan combination tablets and amlodipine tablets, and the test and reference tablets were bioequivalent.