Assessment of Gastrointestinal Blood Loss After Receiving Aspirin or Aspirin Plus Rivaroxaban, or Aspirin Plus REGN9933, or Aspirin Plus REGN7508 in Healthy Adult Participants

A Parallel Group Study in Healthy Participants to Quantitate Increases in Subclinical Gastrointestinal Blood Loss Following Administration of Aspirin Alone or in Combination With Rivaroxaban or Factor XI Inhibitors (REGN9933 or REGN7508)

This study is researching experimental drugs called REGN9933 and REGN7508 (called "study drugs") and comparing their effects to approved treatments of rivaroxaban and aspirin (called "standard treatments"). Aspirin will be given alone or in combination with the study drugs or the other standard treatments to look at their effects on blood loss in the intestines.

The aim of the study is to see if aspirin alone or the study drugs REGN9933 and REGN7508, when taken with aspirin, cause less minor intestinal bleeding than standard treatments rivaroxaban with aspirin.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drug
• How much study drug is in the blood at different times
• Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects)

Key Inclusion Criteria:

1. Body mass index between 18.0 and 32.5 kg/m2 (inclusive) at the screening visit
2. Judged by the investigator to be in good health based on medical history, physical examination, vital sign measurements, and electrocardiograms (ECGs) performed at screening and/or prior to administration of initial dose of study treatment
3. Normal aPTT, normal PT, and normal platelet counts at screening period and at the day 1 visit as defined by the local laboratory
4. Hemoglobin values within the normal range, per local laboratory, at the screening and day 1 visits
5. Negative FOBT at Baseline (visit 2) and visit 3 as defined in the protocol

Key Exclusion Criteria:

1. History of any major surgical procedure or clinically significant physical trauma in the last 6 months, in the opinion of the investigator, that may pose a risk to the participant by study participation
2. Whole blood donation within the previous 56 days or plasma donation within the previous 7 days prior to the screening visit
3. Hospitalized for any reason within 30 days of the screening visit
4. Estimated glomerular filtrate rate (eGFR) of <60 mL/min/1.73m2 at screening as described in the protocol.
5. Current smoker or former smoker, including e-cigarettes, who stopped smoking within 12 months prior to the screening visit
6. History of illicit drug or alcohol abuse within the last 2 years prior to the day 1 visit
7. Use of any prescription and nonprescription medications or nutritional supplements from approximately 2 weeks or 5 half-lives, as described in protocol
8. Has elective surgery planned to occur prior to end of study (EOS)

Note: Other Protocol Defined Inclusion/ Exclusion Criteria Apply