Quantification of Idelalisib in Human Plasma by Ultra-Performance Liquid Chromatography Coupled to Mass Spectrometry in Negative Ionization Mode

Background: Idelalisib is the first orally active selective phosphatidylinositol 3-kinase delta inhibitor approved by Food and Drug Administration and European Medicines Agency in 2014 for the treatment of several types of blood cancer. Idelalisib is widely used as a monotherapy or in combination with rituximab, bendamustine, or ofatumumab with a significant efficacy. However, idelalisib has shown increased risk of infection and a higher frequency of serious adverse events. It may be useful to determine idelalisib concentration in human plasma to adjust dose and to manage adverse effects in clinical practice. Methods: After a single-step protein precipitation of plasma samples. the chromatographic separation was performed using an ultra-high performance liquid chromatography system coupled with mass tandem spectrometry in a negative ionization mode using isotope-labeled internal standard. This method was validated by studies of its linearity, accuracy, imprecision, limit of quantification, recovery, matrix effect, selectivity, and stability. Results: The quantification method was linear from 10 to 2500 ng/mL with a 5 ng/mL lower limit of quantification that encompasses the clinical range of drug concentration. The intraday and interday imprecisions were below 8.1% and 11.4%, respectively. The recoveries and matrix effect of idelalisib were 85.6% +/- 1.2% and 95.7% +/- 3.0%, respectively, which are consistent, precise, and reproducible (coefficient of variation % < 15%). Peak plasma concentration and trough plasma concentration ranges of idelalisib reached 1591-1937 ng/mL and 256.3-303.3 ng/mL, respectively, in 3 follicular lymphoma patients treated with idelalisib 150 mg twice a day. Conclusions: A robust and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated to quantify idelalisib concentration in human plasma. This method was effectively applied to 3 follicular lymphoma patients.