Apixaban and Rivaroxaban Anti-Xa Concentration Utilization in Clinical Practice

Drug-specific anti-Xa concentrations can be used to assess the presence of drug effects; however, there is inadequate guidance for clinicians on the interpretation and clinical application of these results. The purpose of this study is to review patients' first apixaban and rivaroxaban anti-Xa concentrations to identify indications for monitoring and common therapeutic interventions made based on the results. In addition, we compared bleeding and thrombotic outcomes between the obesity group body mass index ≥40 kg/m 2 and the standard group body mass index 25-39.9 kg/m 2 . A retrospective analysis was conducted at a large academic medical center from January 1, 2020, to December 31, 2020. Primary outcomes were indications for anti-Xa concentrations and interventions on results. A total of 180 patients were included in the analysis, with 119 patients (66%) in the apixaban group and 61 patients (34%) in the rivaroxaban group. The most common indications for anti-Xa concentrations were extreme body weight (23%) and concern for bleeding (22%). About half of the anti-Xa concentrations resulted in therapy changes including holding for procedure, switching to heparin or enoxaparin, holding for an elevated anti-Xa concentration or concern for bleeding, adjusting direct-acting oral anticoagulant dose, or switching to an alternative oral anticoagulant. There were no differences in bleeding complications (5% [2] vs. 16% [14], P = 0.11) or thrombotic complications (8% [3] vs. 9% [8], P = 0.85) between the obesity group and the standard group. Despite the lack of validation of therapeutic ranges for anti-Xa concentrations, this study showed clinical situations where anti-Xa concentration monitoring can be of value.