Liquid chromatography–tandem mass spectrometric assay for the T790M mutant EGFR inhibitor osimertinib (AZD9291) in human plasma

• A quick and simple validated method for the quantitative analysis of osimertinib.
• Salt-assisted extraction provides quick and clean extraction for quantitative analysis.
• Assay is suitable for quantification of osimertinib in heparin and EDTA plasma.

A method for the quantitative analysis by ultra-performance liquid chromatography–tandem mass spectrometry of the highly selective irreversible covalent inhibitor of EGFR-TK, osimertinib in human plasma was developed and validated, using pazopanib as an internal standard. The validation was performed in a range from 1 to 1000 ng/ml, with the lowest level corresponding to the lower limit of quantitation. Gradient elution was performed on a 1.8 μm particle trifunctional bonded C18 column by 1% (v/v) formic acid in water, and acetonitrile as mobile phase. The analyte was detected in the selected reaction monitoring mode of a triple quadrupole mass spectrometer after positive ionization with the heated electrospray interface. Within-day precisions ranged from 3.4 to 10.3%, and between-day precisions from 3.8 to 10.4%, accuracies were 95.5–102.8%. Plasma (either lithium heparin or sodium EDTA) pretreatment was performed by salting-out assisted liquid–liquid extraction using acetonitrile and magnesium sulfate. This method was used to analyze the osimertinib blood plasma levels of five adult patients with metastatic T790M mutated non-small cellular lung carcinoma for therapeutic drug monitoring purposes.