Conference Coverage

Andexanet alfa effectively reverses factor Xa inhibition



Andexanet alfa rapidly reverses factor Xa inhibition and effectively establishes hemostasis in patients with acute major bleeding, according to a study presented at the International Stroke Conference sponsored by the American Heart Association. The medication is associated with a low rate of mortality resulting from intracerebral hemorrhage (ICH), compared with the general population of patients with ICH receiving anticoagulation.

Dr. Truman John Milling Jr.

Dr. Truman John Milling Jr.

Factor Xa inhibitors such as apixaban and rivaroxaban effectively prevent thromboembolic events but may cause or exacerbate acute major bleeding. Andexanet alfa, a modified, recombinant, inactive form of human factor Xa, was developed and approved as a reversal agent for factor Xa inhibitors. In a 2015 study, andexanet rapidly and safely reversed anti–factor Xa activity in large cohorts of patients without bleeding.

A single-cohort study

Truman John Milling Jr., MD, an emergency medicine physician at Dell Seton Medical Center at the University of Texas in Austin, and his colleagues conducted the Andexanet Alfa, a Novel Antidote to the Anticoagulation Effects of Factor Xa Inhibitors (ANNEXA-4) study to evaluate the drug’s safety and efficacy in patients with acute major bleeding associated with treatment with a factor Xa inhibitor. For participants to be eligible, their bleeding had to be life threatening with signs of hemodynamic compromise, be associated with a decrease in hemoglobin level of at least 2 g/dL, or occur in a critical organ such as the brain. An independent academic committee determined whether patients met these criteria.

The trial’s primary efficacy outcomes were change from baseline in anti–factor Xa activity and the percentage of patients with excellent or good hemostatic efficacy at 12 hours. The primary safety endpoints were death, thrombotic events, and the development of neutralizing antibodies to andexanet or to native factor X and factor Xa. The efficacy population included patients with major bleeding and baseline anti–factor Xa activity of at least 75 ng/mL. The safety population included all patients who received a dose of andexanet. The independent committee adjudicated the efficacy and safety outcomes.

Hemostasis was sustained for 12 hours

The investigators enrolled 352 participants into the study, all of whom received andexanet and were followed for at least 30 days or until death. The population’s mean age was 77 years. “These were older and sicker patients with a significant amount of comorbid disease,” said Dr. Milling. The primary indication for anticoagulation was atrial fibrillation in 80% of patients. The primary site of bleeding was intracranial in 64% of patients and gastrointestinal in 26% of patients. The remaining 10% of patients had bleeding affecting other areas (such as pericardial or intramuscular bleeding).

The investigators included 254 patients in the efficacy population. At the end of the administration of the andexanet bolus, the median value for anti–factor Xa activity decreased by 92% among participants receiving apixaban, 92% among participants receiving rivaroxaban, and 75% among patients receiving enoxaparin. Among patients receiving apixaban, the median value for anti–factor Xa activity was decreased by 32% at 4 hours, 34% at 8 hours, and 38% at 12 hours. Among patients receiving rivaroxaban, the median value for anti–factor Xa activity was decreased by 42% at 4 hours, 48% at 8 hours, and 62% at 12 hours.

Dr. Milling and his colleagues assessed hemostatic efficacy in 249 patients. Of this group, 82% achieved good or excellent hemostasis. Among participants with good or excellent hemostasis, 84% had excellent results, and 16% had good results. Subanalysis by factor Xa inhibitor, type of bleed, age, and dose of andexanet did not alter the findings significantly.

To determine whether hemostasis had been sustained sufficiently to prevent clinical deterioration, the investigators examined 71 patients with ICH and a single-compartment bleed. From 1 hour to 12 hours, one patient’s outcome changed from excellent/good to poor/none, and one patient’s outcome changed from excellent to good. For the majority of these patients, however, good hemostasis was sustained from 1 to 12 hours.

The rate of thromboembolic events was 9.7%, which is in the expected range for this population, said Dr. Milling. These events were distributed evenly among the 4 weeks of the study. Stroke and deep vein thrombosis accounted for most of these events, and pulmonary emboli and heart attacks occurred as well. “Once we restarted oral anticoagulation ... there were no more thrombotic events,” said Dr. Milling. No patient developed neutralizing antibodies to factor X or factor Xa, nor did any patient develop neutralizing antibodies to andexanet.

The overall mortality rate was 13.9%. The rate of mortality resulting from ICH was 15%, and the rate of mortality resulting from gastrointestinal bleeding was 11%. These results are impressive, considering that patients had received anticoagulants, said Dr. Milling.

Portola Pharmaceuticals, the maker of andexanet alfa, funded the study. Dr. Milling reported receiving funding and honoraria from the Population Health Research Institute at McMasters University, Janssen, CSL Behring, and Octapharma. He also received a small research payment from Portola Pharmaceuticals. Several of the investigators reported receiving funding from Portola Pharmaceuticals.

SOURCE: Milling TJ et al. ISC 2019, Abstract LB7.

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