An improved LC-MS/MS method for determination of cinacalcet in human plasma and its application to the evaluation of food intake effect on the pharmacokinetics of cinacalcet in healthy volunteers.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of cinacalcet in human plasma was developed and validated. This assay was based on liquid-liquid extraction and cinacalcet-d4 was used as an internal standard (IS). Separation was achieved on a C18 column by the mobile phase A of water (containing 0.1% formic acid) and the mobile phase B of acetonitrile-water (95:5, v/v) (containing 0.2% formic acid) with gradient elution. Quantification was done using multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 358.2 → m/z 155.2 for cinacalcet and m/z 362.3 → m/z 155.0 for IS at positive ionization mode. The calibration curve was established over the range 0.05-20.0 ng/mL and the correlation coefficient was >0.99. The intra- and inter-day relative standard deviations were <5.8%. Accuracy determined at four concentrations ranged between 96.0 and 106.0%. This method was successfully applied to a pharmacokinetic description of oral dose of cinacalcet and the significant effect of food intake on the pharmacokinetics of cinacalcet was first demonstrated in Chinese healthy volunteers.