Apixaban and rivaroxaban anti-Xa level utilization for guidance of administration of andexanet alfa: a case series

Background: Andexanet alfa, a modified recombinant factor Xa (FXa), was FDA approved in 2018 for anticoagulant reversal in patients with life-threatening bleeding associated with FXa inhibitors (FXaI). The ANNEXA-4 investigators administered andexanet alfa to patients within an 18-h from last dose of oral FXaI. In practice, time from last dose is often unknown. Previous studies have shown that clearance of these agents may be impaired by renal and hepatic dysfunction, as well as drug-drug interactions. Decision for use of andexanet alfa is also complicated by its high cost, limited drug availability, and thrombotic risk. This study aimed to describe the utility of anti-Xa DOAC levels as a decision point to administer andexanet alfa. Methods: This is a case series of four patients with an anti-Xa DOAC level that received andexanet alfa for oral FXaI reversal in the setting of life-threatening bleeding or prior to procedure. Results: Four patients were included in the study. Two patients had a known time since last dose of oral FXaI. All patients had a detectable anti-Xa DOAC levels prior to administration of andexanet alfa. Two patients had levels within the peak range, one patient had a level below the peak range, and one patient had a level above the peak range. Andexanet alfa was administered after anti-Xa DOAC level return in all patients. Conclusion: In our case series, obtaining anti-Xa DOAC levels prior to administration of andexanet alfa was achievable and facilitated use of reversal agents in patients with major bleeding or emergent procedural need.