Andexanet Alfa (Andexxa) Formulary Review

Andexanet alfa, a recombinant modified human "decoy" factor Xa (FXa) protein, is the first and only available antidote approved by the Food and Drug Administration to manage life-threatening or uncontrolled bleeding associated with the anti-Xa agents. It binds to direct and indirect anti-Xa oral anticoagulants with high specificity to reverse their inhibitory effects and restore the activity of FXa. Andexanet alfa is administered via two different dosing regimens, standard and high dose, based on the specific FXa inhibitor, dose, and time since the patient's last dose of FXa inhibitor. The approval for andexanet alfa is supported by data from two phase 3 studies (ANNEXA-A, ANNEXA-R) and preliminary data from the phase 3b/4 ANNEXA-4 trial. The first study found that andexanet alfa rapidly reduced anti-Xa activity by 92%-94% in healthy volunteers taking apixaban or rivaroxaban. The ANNEXA-4 study found that the median anti-Xa activity decreased by 89%-93% in patients with major bleeding taking apixaban or rivaroxaban. However, thrombotic events occurred in 12 of 67 patients (18%) during the 30-day follow-up in ANNEXA-4. Additionally, only 40% of patients had restarted anticoagulation and, in this group, the rate of thrombotic events was 12%. Four patients had a thrombotic event within 3 days after andexanet alfa treatment. The wholesale acquisition cost of the standard dose regimen is $24,750, and the high-dose regimen is $49,500. The estimated annual drug budget of treating 10-100 patients ranges from $248K to $495M. Effective October 1, 2018, Medicare will provide an add-on payment for andexanet alfa of up to $14,063 per qualifying case to Inpatient Prospective Payment System-participating acute care hospitals. In this formulary review for a health system's pharmacy and therapeutics committee, andexanet alfa clinical trials and medication package insert were summarized and, after consulting with clinical experts from our institutions, practical recommendations for use were generated to ensure appropriate and safe use of this agent.