Direct oral anticoagulants (DOACs) are prescribed for systemic anticoagulation. Fixed doses are recommended, but dose individualization may be warranted. Functional coagulation assays may be available, but their use requires knowledge of the drug taken. To provide alternative methodology for guiding dosage, we have developed and validated a liquid chromatography–mass spectrometric assay for apixaban, dabigatran, edoxaban, and rivaroxaban at the concentrations attained during therapy.
Samples, calibrators, and internal quality controls (100 μL) were mixed with internal standard solution (50 μg/L both dabigatran-13C6 and rivaroxaban-13C6 in acetonitrile) and, after centrifugation (16,400g, 4 minutes), supernatant (100 μL) was injected onto a Cyclone-C18-P-XL TurboFlow column. Analytes were focused onto an Accucore PhenylHexyl (2.1 × 100 mm, 2.6 μm) analytical column and eluted using a methanol + acetonitrile (1 + 1):aqueous ammonium acetate (10 mmol/L) gradient. Data were acquired using high-resolution mass spectrometry in full-scan mode (100–2000 m/z) with data-dependent fragmentation to confirm peak identity. Calibration was linear (1–500 μg/L all analytes).
Total analysis time was 6 minutes. Intra-assay imprecision (% RSD) at 1 μg/L was 2.6%, 4.2%, 17.3%, and 9.5% for apixaban, dabigatran, edoxaban, and rivaroxaban, respectively. Mean recovery was 96%–101%. No signal suppression or enhancement was observed. Apixaban, dabigatran, and rivaroxaban were stable over 3 freeze–thaw cycles, after storage at room temperature, and at 2–8°C for up to 2 weeks. Edoxaban was stable over 3 freeze–thaw cycles but showed a mean deterioration of 16% if stored at 2–8°C (2 weeks) and of 18% and 70% (1 day and 2 weeks, respectively) at room temperature.
The method is suitable for high-throughput therapeutic drug monitoring of DOACs. The acquisition of full scan data allows for the retrospective identification of metabolites. The method can be used to identify a particular DOAC if information on the drug taken is lacking.