Apixaban and Rivaroxaban Anti-Xa Concentrations 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. Additionally, we compared bleeding and thrombotic outcomes between the obesity group BMI ≥ 40 kg/m2 and standard group BMI 25-39.9 kg/m2. 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 upon 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 concentrations or concern for bleeding, adjusting DOAC 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 standard group. Despite the lack of validation of therapeutic ranges for anti-Xa concentrations, this study showed clinical situations where anti-Xa concentrations monitoring can be of value.