For therapeutic drug monitoring (TDM) of axitinib, the new volumetric absorption microsampling technology (VAMS™) was applied to obtain capillary blood samples in an ambulatory setting and the results were compared to plasma samples as the gold standard. On-line solid phase extraction (SPE) applying a Turboflow HTLC Cyclone™ 1.0 × 500 mm column was used to reduce costs and working time. For the analytical separation, a Kinetex 2.6 µm C18 100 Å, 100 × 3.0 mm column with a flow rate of 0.3 mL/min in gradient mode was utilised. The mobile phase consisted of acetonitrile, water and formic acid (A: 05:95:0.1 v/v and B: 95:05:0.1 v/v). For the detection, a single-quadrupole MS detector was used. Through the use of on-line SPE technology, it is possible to reach a LLOQ of 0.5 µg/L from a 10 µL capillary blood sample. For lower concentrations, a MS/MS-detector coupled with the same chromatographic system was applied reaching a LLOQ of 0.04 µg/L. This newly developed method was validated with both detectors at different calibration ranges for plasma and capillary blood as matrix. The precision of the within- and between-runs was within a range of 0.6-7.8% and 1.8 - 14% CV, respectively, while the accuracy was within a range of 81.2-115% and 87.7-116%, respectively. A reliable, simple, less personnel-intensive and cost-efficient extraction and analysis LC-MS and LC-MS/MS method could be developed and validated, which is applicable in ambulatory and clinical care.
Keywords: On-line SPE-LC-MS; Renal cell carcinoma; Therapeutic drug monitoring (TDM); Trap technology; Tyrosin kinase inhibitor (TKI); Volumetric absorptive microsampling (VAMS).
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