Andexanet alfa: trials just leave us with more questions

Andexanet Alfa in Acute Intracranial Hemorrhage in Patients Receiving an Oral Factor Xa Inhibitor (ANNEXA-I), the first ever randomized controlled trial of a reversal agent for direct oral anticoagulants, was published in 2024. The trial, which randomized patients with intracranial hemorrhage to andexanet alfa or usual care, was mandated by the United States Food and Drug Administration as part of its conditional approval in 2018. This approval was originally based on the single-arm trial, The Andexanet Alfa, a Novel Antidote to the Anticoagulation Effects of Factor Xa Inhibitors (ANNEXA-4). ANNEXA-I was stopped early for benefit and showed a reduction in the number of patients with significant hematoma expansion. However, the study was not powered for clinical endpoints such as disability or death and showed no difference in these outcomes. It did, however, show an increased risk of thrombosis, predominantly stroke with andexanet alfa. In this perspective, I reflect on some of the key criticisms of the trial and the implications for its interpretation.