Simultaneous quantification of idelalisib, fludarabine and lenalidomide in rat plasma by using high-performance liquid chromatography coupled with heated electrospray ionization tandem mass spectrometry

• Highly selective method for the determination of idelalisib, fludarabine and lenalidomide in plasma.
• This is the first LC-MS/MS-based method for simultaneous determination of idelalisib, fludarabine and lenalidomide in plasma.
• Plasma sample clean-up involves a simple liquid–liquid extraction procedures.
• The developed LC-MS/MS-based method was applied successfully for pharmacokinetic study.

A sensitive and reliable high-performance liquid chromatography-mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous quantification of idelalisib, fludarabine and lenalidomide using tolbutamide as an internal standard. Analytes were recovered by liquid–liquid extraction and separated on a reverse phase C18 column (150 mm × 4.6 mm i.d., 5 μm) using methanol:0.1% formic acid buffer (70:30) as mobile phase at a flow rate of 1 mL/min in isocratic mode. Selective reaction monitoring was performed using the transitions, i.e. m/z 416.25/176.48, 286.11/154.10, 260.15/149.15, and 271.14/155.06 to quantify idelalisib, fludarabine and lenalidomide and tolbutamide, respectively. The method was validated over the concentration range of 1.15–576.84 ng/mL for idelalisib, 0.95–476.25 ng/mL for fludarabine and 0.97–486.19 ng/mL for lenalidomide. Intra and inter-day accuracy and precision of validated method were within the acceptable limits of <15%. Coefficients of correlation (r2) for the calibration curves were >0.998 for all analytes. The method was successfully applied for simultaneous estimation of idelalisib, fludarabine and lenalidomide in a pharmacokinetic study in rats.