Validated LC–MS/MS method for quantitation of a selective JAK1 inhibitor, filgotinib in rat plasma, and its application to a pharmacokinetic study in rats

Simultaneous Quantification of Filgotinib and Its Active Metabolite in Human Plasma Using Liquid Chromatography-Tandem Mass Spectrometry: Validation and Clinical Application

Filgotinib (FLG) is a Janus kinase 1 inhibitor and is metabolized to an active metabolite, GS-829845. There is no report on the method for simultaneous quantification of FLG and GS-829845 in clinical samples. We developed a liquid chromatography-tandem mass spectrometry method for simultaneous determination of FLG and GS-829845 in patient plasma. FLG and GS-829845 were extracted from an aliquot of 50 μL of human plasma by simple deproteinization using methanol. Chromatographic separation was performed using a Shim-pack Scepter C18-120 column with a combined mobile phase of water and methanol containing 0.1% formic acid and gradient elution at a flow rate of 0.2 mL/min. Detection was performed by positive electrospray ionization using a QTRAP 4500 mass spectrometer. The method was validated in the concentration range of 2.5-50 ng/mL for FLG and 250-5000 ng/mL for GS-829845. Intra- and inter-day assay accuracy and precision were within 11.4% and 13.9%, respectively. Recoveries and matrix effects were consistent and reproducible. This developed and fully validated method is simple, rapid, and cost-effective and was used successfully for therapeutic drug monitoring in a patient with rheumatoid arthritis.

Validated DBS method for filgotinib quantitation in rat dried blood spots and its application to a pharmacokinetic study in rats

Filgotinib is a selective JAK1 (Janus kinase) inhibitor, showed efficacy in patients suffering from moderate-to-severe rheumatoid arthritis. In this paper, we present the data on the development and validation of a sensitive, selective and high-throughput LC-MS/MS (liquid chromatography with tandem mass spectrometry) method for the quantitation of filgotinib from rat dried blood spot (DBS) cards. To the DBS disc cards, 0.2% formic acid enriched with internal standard (IS) was added and sonicated. Thereafter the extraction of filgotinib and the IS (tofacitinib) was accomplished using ethyl acetate as an extraction solvent. The resolution of filgotinib and the IS was achieved on a Gemini C₁₈ column with an isocratic mobile phase, which is a mixture of 0.2% formic acid:acetonitrile (20:80, v/v) at a flow-rate of 0.9 mL/min. The total run time was 2.90 min and the retention time of filgotinib and the IS was ~1.31 and 0.89 min, respectively. Filgotinib and the IS were analyzed using positive ion scan mode and parent-daughter mass to charge ion (m/z) transition of 426.3→291.3 and m/z 313.2→149.2, respectively, for quantitation. The calibration range was 1.37-1937 ng/mL. No matrix effect and carry over were observed. All the validation parameters met the acceptance criteria. The validated method has been applied to a pharmacokinetic study in rats. A good correlation between DBS and plasma concentrations for filgotinib was observed.