1. ≥ 18 to ≤ 65 years old at the time of screening
2. Hemophilia A or B of any severity, with a documented ≥ 3 months history of inhibitors (≥ 0.6 BU) requiring the use of bypassing agents (FEIBA or rFVIIa) prior to screening. Inhibitor level will be tested at screening if no documented history is available.
3. Hepatitis C virus (HCV) negative, either by antibody testing or polymerase chain reaction (PCR); or HCV positive with stable liver disease
4. Human immune deficiency virus (HIV) negative; or HIV positive with stable disease and CD4 count ≥ 200 cell/mm^3 at screening
5. Adequate venous access
6. Willing and able to comply with the requirements of the protocol
7. If a female of childbearing potential, must have a negative blood pregnancy test and agrees to employ adequate birth control measures for the duration of the study.
8. If female of non-childbearing potential, confirmed at screening.
1. Known hypersensitivity to FEIBA or any of its components
2. Advanced liver disease (e.g., liver biopsy confirmed diagnosis of cirrhosis, portal vein hypertension, ascites, prothrombin time [PT] 5 seconds above upper limit of normal)
3. Planned elective surgery during participation in this study (excluding minor procedures that will not need preventative bleeding treatments, such as exchanges of peripherally inserted central catheters)
4. Platelet count < 100,000/μL
5. Taking Emicizumab (Hemlibra) for bleed prevention
6. Clinical or laboratory evidence of disseminated intravascular coagulation based on medical history
7. Prior history or evidence of thromboembolic event: acute myocardial infarction, deep vein thrombosis, pulmonary embolism, etc.
8. Diagnosis of advanced atherosclerosis, malignancy, and/or other diseases that may increase the participant’s risk of thromboembolic complications
9. Taking any immunomodulating drug (e.g., corticosteroid agents at a dose equivalent to hydrocortisone > 10 mg/day, or α-interferon) within 30 days prior to enrollment except anti-retroviral chemotherapy.
10. Herbal supplements that contain anti-platelet activity
11. Participant has participated in another clinical study involving an investigational product (IP) or investigational device within 30 days prior to enrollment or is scheduled to participate in another clinical study involving an IP or investigational device during the course of this study
12. Family member or employee of the investigator
13. Clinically significant medical, psychiatric or cognitive illness, or recreational drug/alcohol use that, in the opinion of the investigator, would affect participant safety or compliance