Quantification of cinacalcet by LC–MS/MS using liquid–liquid extraction from 50 μL of plasma

A simple and economical high-performance liquid chromatography–positive ion electrospray tandem mass spectrometry method was developed and validated for the quantification of cinacalcet in plasma. Following liquid–liquid extraction, the analyte was separated using an isocratic mobile phase on a reversed-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 358–155 for cinacalcet and m/z 310–148 for the internal standard. The assay exhibited a linear dynamic range of 0.1–200 ng/mL for cinacalcet in plasma. Acceptable precision (<10%) and accuracy (100 ± 5%) were obtained for concentrations over the standard curve range. A run time of 3.5 min for each sample made it possible to analyze more than 250 samples per day. The method was successfully applied to quantify cinacalcet concentrations in a preclinical pharmacokinetic study after a single oral administration of cinacalcet at 10 mg/kg to rats. Following oral administration the maximum mean concentration in plasma (Cmax; 160 ± 56 ng/mL) was achieved at 1.0 h (Tmax), area under the curve (AUC) and half-life (t1/2) were 949 ± 257 ng h/mL and 3.58 ± 0.4 h, respectively.