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Safety of two new clot-preventing medicines for adults with atrial fibrillation on anticoagulation

A Phase 2, Randomized, Multicenter, Open-label, Blinded-endpoint Study to Evaluate the Safety of REGN7508 and REGN9933, Monoclonal Antibodies Against FXI, Versus Apixaban in Participants With Atrial Fibrillation (ROXI-ATLAS)

Phase 2 Interventional Regeneron Pharmaceuticals · NCT07175428

This trial will test two experimental medicines, REGN7508 and REGN9933, against apixaban to see if they prevent clots with acceptable bleeding risk in adults with atrial fibrillation who need long-term anticoagulation.

Quick facts

PhasePhase 2
Study typeInterventional
Enrollment1200 (estimated)
Ages18 Years and up
SexAll
SponsorRegeneron Pharmaceuticals Industry-sponsored
Locations45 sites (Dothan, Alabama and 44 other locations)
Trial IDNCT07175428 on ClinicalTrials.gov

What this trial studies

In this Phase 2 interventional study, adults with atrial fibrillation who require indefinite anticoagulation are assigned to receive REGN7508, REGN9933, or the approved anticoagulant apixaban. The study compares bleeding events, stroke and systemic embolism rates, and records side effects to characterize safety and tolerability. Investigators will also measure drug concentrations over time and check for antibodies the body might make against the investigational medicines. Key enrollment criteria include CHA2DS2-VA score thresholds and an INR <2.5 at randomization for participants on warfarin.

Who should consider this trial

Good fit: Adults with non‑valvular atrial fibrillation or flutter who need long-term anticoagulation and meet the study's CHA2DS2-VA score and other enrollment criteria are the intended participants.

Not a fit: People with mechanical heart valves, known moderate-to-severe mitral stenosis, or other protocol exclusions (such as recent successful ablation per the protocol) would not be expected to benefit from this study.

Why it matters

Potential benefit: If successful, these medicines could prevent strokes and other clot-related events while potentially reducing bleeding risk compared with current anticoagulants.

How similar studies have performed: Approved oral anticoagulants like apixaban have proven benefit in AF, but using investigational agents such as REGN7508 and REGN9933 represents a novel approach with limited prior clinical data.

Eligibility criteria

Show full inclusion / exclusion criteria 
Key Inclusion Criteria:

1. Has AF or flutter (paroxysmal or persistent), not felt to be secondary to a reversible cause, and an indication for indefinite anticoagulation treatment as described in the protocol
2. Meets one of the following:

   1. CHA2DS2-VA \[C: Congestive heart failure; H: Hypertension; A2: Age ≥75 years (double points); D: Diabetes mellitus; S2: Stroke or TIA or Thromboembolism (double points); V: Vascular disease; A: Age 65-74 years\] score ≥2 and Oral Anticoagulant (OAC) naïve or
   2. CHA2DS2-VA score ≥3 or
   3. CHA2DS2-VA score of 2 and at least 1 enrichment criteria as described in the protocol
3. Must have an International Normalization Ratio (INR) \<2.5 at the time of randomization if taking warfarin or another Vitamin K Antagonist (VKA)

Key Exclusion Criteria:

1. Has a mechanical heart valve prosthesis (Note: transcatheter aortic valve replacement is not an exclusion)
2. Has known moderate-to-severe mitral stenosis
3. Has had successful ablation therapy or Left Atrial Appendage (LAA) occlusion/exclusion, or planned ablation or LAA occlusion/exclusion as described in the protocol
4. Had an ischemic stroke within 2 days prior to randomization
5. Has estimated Glomerular Filtration Rate (eGFR) \<15 mL/min/1.73m\^2 within 30 days prior to randomization or on dialysis or expected to be started as described in the protocol
6. Has a history of central nervous system bleeding within 30 days prior to randomization

Note: Other protocol-defined Inclusion/ Exclusion criteria apply

Where this trial is running

Dothan, Alabama and 44 other locations

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Atrial FibrillationBleedingStrokeSystemic embolismBlood clots
Last reviewed 2026-06-10 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.