Clinical implication of monitoring rivaroxaban and apixaban by using anti‐factor Xa assay in patients with non‐valvular atrial fibrillation

Background Although patients taking non‐vitamin K antagonist oral anticoagulants (NOACs) do not require routine coagulation monitoring, high‐risk patients require monitoring to assess pharmacodynamics. Methods We measured (1) anti‐factor Xa activity (AXA), using chromogenic assay with the HemosIL Liquid Heparin kit, (2) prothrombin time (PT), and (3) activated partial thromboplastin time (aPTT) in 188 blood samples from 70 patients with non‐valvular atrial fibrillation, of whom 36 received rivaroxaban once daily and 34 received apixaban twice daily. Results After the rivaroxaban therapy, AXA ranged from 0 to 3.65 IU/mL; PT, from 9.6 to 44.5 s; and APTT, from 19.3 to 69.7 s. After the apixaban therapy, AXA ranged from 0.02 to 3.18 IU/mL; PT, from 10.2 to 20.8 s; and APTT, from 21.8 to 59.8 s. At peak time, the AXA of patients who received rivaroxaban and apixaban were almost the same (2.08±0.91 IU/mL vs. 1.71±0.57 IU/mL), but the PT and APTT of patients who received rivaroxaban were more prolonged than those of patients who received apixaban (18.1±5.6 s vs. 13.8±0.9 s, p <0.001 and 40.9±7.3 s vs. 35.5±7.5 s, p <0.01, respectively). At trough time, the AXA and PT of patients who received rivaroxaban were respectively lower and shorter than those of patients who received apixaban (0.28±0.31 IU/mL vs. 1.04±0.72 IU/mL, p <0.001 and 11.9±2.0 s vs. 13.7±2.4 s, p <0.01, respectively), but the APTT of patients who received rivaroxaban and apixaban did not significantly differ (32.3±4.3 s vs. 34.3±3.8 s). Conclusions Measurement of AXA might be useful to assess the pharmacodynamics of high‐risk patients, such as high age, low body weight, and/or low renal function, and to assess the intensity of anticoagulation by using different methods of administration, such as crushed tablet via the nasogastric tube.