Micromethod for quantification of cinacalcet in human plasma by liquid chromatography-tandem mass spectrometry using a stable isotope-labeled internal standard

BACKGROUND: Cinacalcet hydrochloride is a calcimimetic agent indicated for the treatment of secondary hyperparathyroidism in dialysis-dependent patients with chronic kidney disease. In the context of a pharmacokinetic (PK)/pharmacodynamic study of cinacalcet in dialysis-dependent chronic kidney disease children with secondary hyperparathyroidism, we describe the development and validation of a new, rapid, simple, and economical liquid chromatography-tandem mass spectrometry (LC-MS/MS) micromethod for quantifying cinacalcet plasma concentrations. METHODS: Cinacalcet was analyzed in 50-μL plasma samples over a wide range of concentrations (0.1-100 ng/mL) by LC-MS/MS after protein precipitation and addition of deuterated cinacalcet as the internal standard. Cinacalcet was quantified using selective reaction monitoring of the specific transition m/z 358.1 > 155.1, with the 361.1 > 158.1 transition used for the internal standard. The suitability of the assay for clinical PK studies was evaluated using data from a pilot PK study in a pediatric patient. RESULTS: The overall turnaround time for the assay was 20 minutes. The lower limit of quantification of the method was 0.1 ng/mL. Intraassay imprecision and inaccuracy for quality control samples ranged from 2.8% to 9% and 100% to 102%, respectively. Interassay imprecision and inaccuracy ranged from 6.9% to 8.5% and 99% to 103%, respectively. The overall recovery ranged from 90% to 106%. No ion suppression due to matrix effects was found with different preanalytical conditions, such as hemolysis, lipemia, and hyperuricemia. CONCLUSIONS: This LC-MS/MS micromethod provides high specificity, precision, and accuracy for rapid quantification of cinacalcet plasma concentrations, and it is suitable for application in pediatric PK studies; it also has potential for use in the establishment of target ranges and ultimately routine therapeutic drug monitoring to optimize cinacalcet dosing.