Monitoring anti-factor Xa activity in patients with chronic thromboembolic pulmonary hypertension treated with factor Xa inhibitors

Direct oral anticoagulants (DOACs) have been used clinically in patients with chronic thromboembolic pulmonary hypertension (CTEPH) for secondary prevention after acute venous thromboembolism, although the data are limited. We evaluated the effects of DOACs-especially factor Xa (FXa) inhibitors-by measuring anti-factor Xa activity (AXA). Fifty consecutive CTEPH patients treated with rivaroxaban, apixaban, or edoxaban were enrolled. Heparin-calibrated AXA was measured at peak and trough. The median peak heparin-calibrated AXA across all 50 patients was 1.90 IU/mL and was comparable among the three FXa inhibitors. At trough, heparin-calibrated AXA was significantly higher in apixaban-treated patients (median 0.70 IU/mL) than in those given rivaroxaban (median 0.11 IU/mL) or edoxaban (median 0.11 IU/mL, p < 0.001). Peak heparin-calibrated AXA was significantly lower with reduced-dosage FXa inhibitor (edoxaban 30 mg/day) than with the reference dosage (edoxaban 60 mg/day, apixaban 10 mg/day, or rivaroxaban 15 mg/day, p = 0.01). The heparin-calibrated AXA of both rivaroxaban and apixaban was strongly significantly correlated with the plasma concentration of each drug. The cumulative rate of major and clinically relevant non-major bleeding was significantly higher in patients with peak heparin-calibrated AXA ≥ 2.09 IU/mL. Heparin-calibrated AXA could provide useful information for treating CTEPH patients with FXa inhibitors.