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 (C(max); 160±56 ng/mL) was achieved at 1.0 h (T(max)), area under the curve (AUC) and half-life (t(½)) were 949±257 ng h/mL and 3.58±0.4 h, respectively.