Trial of Andexanet in Patients Receiving an Oral FXa Inhibitor Who Require Urgent Surgery

Inclusion Criteria: All of the following criteria must be met for the patient to be eligible: * Either the patient or their medical proxy (or legal designee) has given written informed consent. * Age ≥ 18 and \< 85 years old. * Requires urgent surgical intervention that must occur within 12 hours of consent, for which reversal of anti-fXa activity is judged necessary. * Treatment with an oral FXa inhibitor (apixaban \[last dose 2.5 mg or greater\], rivaroxaban \[last dose 10 mg or greater\], edoxaban \[last dose 30 mg or greater\] or enoxaparin \[≥ 1 mg/kg/d\]): * ≤ 15 hours prior to start of surgery. * \> 15 hours prior to start of surgery or unknown time from the last dose, if documented anti fXa activity is \> 100 ng/mL (\> 0.5 IU/mL for enoxaparin, or over the equivalent IU/mL threshold on a low molecular weight heparin assay; see Laboratory Manual) within 2 hours prior to consent. Note: Patients enrolled in this manner should receive a high-andexanet dosing regimen. * Have a negative pregnancy test documented prior to enrollment (for women of childbearing potential). * Willingness to use highly effective methods of contraception through 30 days following study drug dose (for female and male patients who are fertile). Exclusion Criteria: If a patient meets any of the following criteria, he or she is not eligible: * Surgery for which the risk of clinically meaningful uncontrolled or unmanageable bleeding is low. * Acute life-threatening bleeding (ISTH criteria) at the time of Screening: 1. The patient has acute-overt bleeding that is potentially life-threatening, e.g., with signs or symptoms of hemodynamic compromise, such as severe hypotension, poor skin perfusion, mental confusion, low urine output that cannot be otherwise explained. 2. The patient has overt bleeding associated with a fall in hemoglobin level by ≥2g/dL, OR, a hemoglobin ≤8 g/dL if no baseline hemoglobin is available. 3. The patient has acute bleeding in a critical area or organ, such as pericardial, intracranial, or intraspinal. * Any surgical procedure that involves the intraoperative use of systemic, intravascular, unfractionated heparin. * Primary procedure for efficacy assessment is a non-surgical interventional procedure (e.g, lumbar puncture, skin biopsy, cardiac catheterization, endoscopic retrograde cholangio-pancreatography). * Expected survival of \< 1 month due to comorbidity. * Known "Do Not Resuscitate" order or similar advanced directive. * The patient has a recent history (within 30 days prior to screening) of a diagnosed TE as follows: venous thromboembolism (including deep vein thrombosis, pulmonary embolism, intracardiac thrombus), myocardial infarction (including asymptomatic troponin elevations), disseminated intravascular coagulation, acute traumatic coagulopathy, cerebrovascular accident, transient ischemic attack, unstable angina pectoris hospitalization, or severe peripheral vascular disease. * Acute decompensated heart failure or cardiogenic shock at the time of screening. * The patient has sepsis or septic or severe hemorrhagic shock at the time of Screening. * The patient has heparin-induced thrombocytopenia (with or without thrombosis). * Inherited coagulopathy (e.g., anti-phospholipid antibody syndrome, protein C/S deficiency, Factor V Leiden) at time of Screening. * Platelet count \< 80,000/µL at the time of Screening. * Last dose of apixaban \< 2.5 mg, rivaroxaban \< 10 mg, edoxaban \< 30 mg, or enoxaparin 40 mg. * The patient is pregnant or a lactating female. * The patient has received any of the following drugs or blood products within 7 days of enrollment: * Vitamin K antagonists (e.g., warfarin). * Dabigatran. * Prothrombin complex concentrate products (e.g., Kcentra®) or recombinant factor VIIa (e.g., NovoSeven®). * Whole blood, plasma fractions. Note: Administration of tranexamic acid, platelets or packed red blood cells is not an exclusion criterion. * The patient was treated with an investigational drug \< 30 days prior to Screening. * Prior treatment with andexanet. * Known hypersensitivity to any component of andexanet. * Known allergic reaction to hamster proteins. * Known or suspected (i.e., presumed positive) COVID-19-related illness at the time of Screening.