Direct Oral to Parenteral Anticoagulant Transitions: Role of Factor Xa Inhibitor‐Specific Anti‐Xa Concentrations

Objectives The increasing use of oral factor Xa inhibitors (FXaI) has led to a growing interest in the clinical utility of laboratory monitoring to enhance safety and effectiveness. Particularly, the use of FXaI-specific anti-Xa concentrations has gained traction and been advocated for several indications, but limited studies have explored the role of anti-Xa concentrations in guiding inpatient transitions from oral to parenteral anticoagulants. Therefore, additional data on such approaches are warranted to help balance bleeding and thrombotic risks in the higher acuity inpatient setting. This study sought to compare two strategies for oral-to-parenteral anticoagulant transitions: FXaI anti-Xa concentration-guided versus standard of care (i.e., per-package insert). Study Design This was an observational, single-center, retrospective cohort study conducted from May 2016 to May 2021. Hospitalized patients converted from an oral FXaI (apixaban or rivaroxaban) to therapeutic parenteral anticoagulation with or without FXaI anti-Xa concentration guidance were reviewed. The primary outcome of major bleeding, according to the International Society on Thrombosis and Hemostasis criteria, was compared between groups. Cox proportional hazard modeling was used to evaluate patient characteristics associated with major bleeding events. Results A total of 845 patients (388 in the concentration-guided group and 457 in the non-concentration-guided group) met the inclusion criteria. Major bleeding was significantly lower in the concentration-guided versus the non-concentration-guided group (2.2% vs. 11.3%; p < 0.001, respectively). There were no differences between the groups in thromboembolic complications (1.8% concentration guided vs. 1.5% non-concentration guided; p = 0.72) despite a significantly longer time from last oral FXaI dose to parenteral anticoagulant initiation in the concentration-guided group (27.9 h vs. 15.1 h; p < 0.01). The concentration-guided group had an 80% lower risk of major bleeding compared with the non-concentration-guided group (adjusted hazard ratio [HR] 0.20, 95% confidence interval [CI] 0.10-0.39; p < 0.01). Conclusions This analysis suggests using FXaI anti-Xa concentrations to guide the transition from oral to parenteral anticoagulants may be beneficial in reducing major bleeds in select patient populations.