A Single Health System Retrospective Qualitative Analysis of Inpatient Apixaban and Rivaroxaban Calibrated Anti-Xa Level Monitoring and Clinical Implications.

Introduction: The ability to obtain a quantitative drug level for apixaban and rivaroxaban exists using drug-specific calibrated anti-Xa assays; however, no standard exists defining when to obtain direct oral anticoagulant (DOAC) concentrations or how to adjust medication regimens based on the results. Objective: Describe the incidence of DOAC levels obtained, identify trends in prescribing DOAC levels in clinical practice, and qualitatively assess level appropriateness and actions taken based on level results. Methods: A qualitative, retrospective analysis was conducted using the electronic medical record to identify adult inpatients within a 10-hospital health system with a calibrated apixaban or rivaroxaban anti-Xa level result from April 1, 2020, to November 1, 2022. The primary endpoint was the incidence of DOAC levels drawn. Secondary outcomes included the percentage of DOAC concentrations that prompted a dose change, association between dose or agent change and concentrations outside the on-therapy range, and association between indication for obtaining DOAC levels and resultant concentrations. Results: One-hundred thirty-two calibrated anti-Xa levels were obtained in 101 inpatients during the study period, representing a level drawn in 0.48% of all apixaban and rivaroxaban orders. Eighty-three (63%) patients were on apixaban. Primary reasons to draw DOAC levels were extreme body weight (35%), treatment failure concerns (23%), bleeding concerns (18%), and drug interactions (14%). Only 42 (31.8%) of all levels were drawn appropriately as a peak. Seventeen (40.4%) of the peak levels were within the on-therapy range. Of the 25 levels outside the on-therapy range, 14 (56%) resulted in no change in therapy. For all levels drawn, 70 (53%) resulted in no change to therapy. Conclusions: DOAC concentrations are often drawn at inappropriate times and seldom influence a dose or agent change. Future research is needed to determine if DOAC concentrations may be clinically meaningful in a select subgroup of patients.