This afternoon in Chicago, the American Heart Association’s Scientific Sessions will hand the cardiovascular world one of the most consequential stroke-prevention readouts of the decade. At 1:45 p.m. CT in the late-breaking science session titled “Treating the Clot or Controlling the Blood Pressure: Improving Outcomes After Stroke,” Bayer’s investigational drug asundexian will receive a full presentation of key new analyses from its pivotal Phase III OCEANIC-STROKE trial, bringing a comprehensive dataset to the global cardiology community.

The result, in brief: a 26% reduction in recurrent ischemic stroke with no meaningful increase in major bleeding, in a trial enrolling more than 12,300 patients across 37 countries. And as of October 26, the drug is no longer investigational everywhere — China’s National Medical Products Administration approved asundexian under the brand name Sunharbo® eleven days ago, making it the world’s first approved Factor XIa (FXIa) inhibitor for any indication.

Why Today’s Session Matters

OCEANIC-STROKE’s primary findings were unveiled at the American Stroke Association’s International Stroke Conference in New Orleans in February, and the full results were published in the New England Journal of Medicine in April. But the AHA Scientific Sessions — the flagship annual meeting for cardiologists, not neurologists — represents a different and broader constituency.

Today’s slot places asundexian before the physicians who manage long-term cardiovascular risk, prescribe anticoagulants, and weigh bleeding against thrombotic events every day. The presentation is grouped alongside the REDUCE trial of spironolactone-based blood pressure management after stroke and the OPTIMAL-Stroke intensive blood-pressure control trial, framing the session around the two dominant post-stroke intervention strategies: antithrombotic therapy and pressure control.

New analyses are also being unveiled. Chief among them is an exploratory subgroup analysis examining whether asundexian’s effect held across patients stratified by baseline vascular risk using the non-laboratory Framingham Risk Score — a question of central importance to cardiologists managing heterogeneous patient populations. The answer was consistent: asundexian lowered ischemic stroke without increasing major bleeding across low, intermediate, and high Framingham risk groups, with no significant interaction across categories.

The Drug and the Mechanism

Asundexian (BAY 2433334) is a once-daily oral inhibitor of activated Factor XIa (FXIa), a protein that sits in the intrinsic, or contact-activation, pathway of the coagulation cascade — the biochemical sequence that converts liquid blood into a clot. The drug’s rationale exploits a subtle but important distinction between how the body clots normally and how it clots pathologically.

Here is the distinction in full: the coagulation cascade has two initiating arms. The extrinsic pathway, triggered by tissue factor released from damaged vessel walls, is the primary mechanism of normal hemostasis — the protective clotting that seals a wound. The intrinsic pathway, in which FXIa plays a central amplification role, is comparatively dispensable for ordinary wound healing. People born with severe deficiency of Factor XI (a condition called hemophilia C) have a markedly reduced tendency to form clots, but they rarely suffer spontaneous, life-threatening bleeds — the strongest natural evidence that the intrinsic pathway can be safely suppressed.

In pathological thrombosis, however — the kind of sustained, amplified clot growth that occludes a cerebral artery and causes a stroke — FXIa-mediated amplification plays a proportionally much larger role. By selectively targeting FXIa, asundexian aims to interrupt the abnormal clot growth that causes ischemic strokes while leaving the body’s ordinary wound-sealing capacity largely intact.

This is not merely a theoretical advantage. Prior-generation anticoagulants — direct oral anticoagulants (DOACs) such as rivaroxaban and apixaban, which target Factor Xa or thrombin downstream in a pathway shared by both the extrinsic and intrinsic arms — carry meaningful bleeding risk, including intracranial hemorrhage. That risk has historically made neurologists and cardiologists reluctant to use anticoagulants in secondary stroke prevention outside the specific indication of atrial fibrillation, where the cardioembolic threat is severe enough to justify the trade-off. FXIa inhibition was designed from the ground up to dissolve that trade-off.

“We’ve reached the limits of the stroke protection that can be achieved with antiplatelets,” said Dr. Andrew Russman, head of Cleveland Clinic’s stroke program and an OCEANIC-STROKE investigator. “FXIa inhibitors are an entirely new class of drugs that are relatively selective — they target the pathological clotting without the same degree of bleeding risk we see from upstream anticoagulants.”

What OCEANIC-STROKE Found

The Phase III OCEANIC-STROKE trial randomized 12,327 patients within 72 hours of a noncardioembolic ischemic stroke or high-risk transient ischemic attack (TIA) to either asundexian 50 mg once daily or placebo, in addition to planned single or dual antiplatelet therapy. The trial was international, double-blind, placebo-controlled, and event-driven, run across 702 sites in 37 countries under the academic leadership of McMaster University’s Population Health Research Institute. Median follow-up was 567 days — close to 19 months.

The primary efficacy endpoint was time to first occurrence of ischemic stroke. The primary safety endpoint was time to major bleeding as defined by the International Society on Thrombosis and Haemostasis.

Primary results: Asundexian reduced ischemic stroke with a cause-specific hazard ratio of 0.74 (95% CI, 0.65–0.84; P

Safety: ISTH-defined major bleeding occurred in 1.9% of patients on asundexian and 1.7% on placebo (HR, 1.10; 95% CI, 0.85–1.44; P=0.46) — a statistically non-significant difference. Symptomatic intracranial hemorrhage and hemorrhagic stroke rates were also comparable between arms. The wide confidence interval around the bleeding hazard ratio means a small increase in absolute risk cannot be fully ruled out, but the trial’s prespecified analysis found no meaningful safety signal.

Secondary outcomes: Asundexian also met composite endpoints including cardiovascular death, myocardial infarction, or stroke; and death from any cause, myocardial infarction, or stroke.

Consistency: The benefit was observed across all stroke subtypes included in the trial’s TOAST classification — large-artery atherosclerosis, small-vessel occlusion, and undetermined etiology. The survival curves for ischemic stroke in the two arms began separating in the early weeks after randomization, with divergence becoming statistically unambiguous and sustained through 19 months — suggesting that the benefit is not limited to the acute post-event window.

“The findings from OCEANIC-STROKE are a notable research achievement,” said Dr. Mike Sharma, the principal investigator at McMaster University and Professor of Neurology. “What we’re seeing is early and sustained separation of the curves — asundexian is protecting patients from recurrent stroke throughout the full follow-up, not just in the early high-risk period.”

Severity, Not Just Incidence

Additional analyses — first presented at the European Stroke Organisation Conference in Maastricht in May — added a clinically important dimension to the efficacy picture: asundexian did not merely prevent more strokes; it appeared to make the strokes that did occur less severe.

Among the 902 incident ischemic strokes that occurred across both arms during the trial (384 in the asundexian group, 518 in the placebo group), those in the asundexian group were significantly less likely to be classified as moderate-to-high severity. Using the NIH Stroke Scale (NIHSS), moderate-to-high severity strokes (NIHSS ≥8) accounted for 22.9% of strokes in the asundexian arm and 30.3% in the placebo arm — a statistically significant difference (p=0.045).

Disabling stroke, defined as a modified Rankin Scale score of 3 or higher (or a one-point increase from baseline in patients with pre-existing disability), occurred in 2.1% of patients in the asundexian group versus 3.0% in the placebo group — a 31% relative reduction in that outcome (cause-specific hazard ratio 0.69; 95% CI, 0.55–0.87). Fatal ischemic stroke occurred in 0.3% of asundexian patients and 0.5% in the placebo group, corresponding to a 43% relative reduction in point-estimate terms, though this individual finding did not reach statistical significance (cause-specific hazard ratio 0.57; 95% CI, 0.31–1.06). Patients who experienced a stroke on asundexian also required acute intervention, such as intravenous thrombolysis or endovascular thrombectomy, at a lower rate — 10.4% versus 15.8%.

For stroke neurologists and cardiologists weighing the drug’s benefit-risk profile, these severity findings carry practical weight: a stroke that leaves a patient with mild deficits rather than severe disability is not simply a lesser version of the same event. It may mean the difference between independent living and long-term institutional care.

“These results are highly significant for stroke clinicians because they add a secondary prevention option without the competing risk of hemorrhage,” said Dr. Richa Sharma, a stroke neurologist at Yale University who was not involved in the trial. “The reductions in both incidence and severity could help patients live longer and disability-free — though we still have open questions about long-term durability and which patients will benefit most. Patient selection will be critical: this would not be appropriate for someone with detected atrial fibrillation, where full anticoagulation remains the standard.”

The Regulatory Clock Is Running

Bayer has moved quickly to translate OCEANIC-STROKE into regulatory submissions worldwide. In May 2026, the FDA accepted the company’s New Drug Application for asundexian for the prevention of ischemic stroke in patients after a noncardioembolic ischemic stroke or TIA, granting it Priority Review designation — a designation reserved for drugs that, if approved, could represent a significant improvement over available therapy for a serious condition. Priority Review shortens the FDA’s target review timeline from the standard 12 months to 6 months. The FDA had previously issued asundexian a Fast Track designation in 2023, facilitating earlier and more frequent interactions during development.

Japan’s Ministry of Health, Labour and Welfare accepted a parallel submission in May 2026. The European Medicines Agency accepted Bayer’s Marketing Authorization Application in June 2026.

And on October 26, 2026 — eleven days ago — China’s National Medical Products Administration granted marketing approval for asundexian 50 mg once daily under the brand name Sunharbo®, making it the world’s first approved Factor XIa inhibitor for any indication.

As of today, asundexian is approved in China and under active Priority Review by the FDA. EMA and Japanese MHLW reviews are ongoing. The drug’s regulatory status has changed substantially since primary results were first published, and the cardiology community attending today’s AHA session arrives with an approved drug already on the market in the world’s most populous country.

A Mixed Class History: What It Teaches About Clot Biology

The FXIa class’s path to today was not entirely smooth — and understanding the stumble is essential to understanding why today’s data matter.

Asundexian itself failed in OCEANIC-AF, a parallel Phase III trial that asked a different question: could it replace apixaban for stroke prevention in atrial fibrillation? The answer was no. That trial was halted early in November 2023 after demonstrating that patients assigned to asundexian experienced substantially higher rates of stroke or systemic embolism than those receiving the standard-of-care DOAC. Reports from the trial’s closure described a hazard ratio of approximately 3.8 — a resounding defeat.

But the OCEANIC-AF failure was not a failure of FXIa inhibition as a concept. It was, in retrospect, a revealing biological lesson about where in the thrombosis spectrum FXIa plays a critical role and where it does not.

In atrial fibrillation, the cardioembolic risk is driven by blood stasis in the left atrial appendage, which produces large thrombi through a process that depends heavily on sustained thrombin generation across both the extrinsic and intrinsic coagulation pathways. Full anticoagulation — blocking FXa or thrombin directly — is needed to prevent these stagnant-blood clots. FXIa inhibition, which targets only one amplification branch, is insufficient for that setting.

In noncardioembolic stroke, by contrast — where atherosclerotic plaque disruption and smaller arterial thrombi are the dominant mechanisms — FXIa-mediated amplification plays a proportionally much larger role. Selective inhibition is both necessary and sufficient. This is not a setback that OCEANIC-STROKE merely overcame; it is a durable mechanistic boundary condition for the class. FXIa inhibitors appear to have a defined therapeutic window: effective for arterial thrombosis driven by plaque, insufficient for large cardioembolic thrombi driven by stasis.

That mechanistic insight has rippled through the competitive landscape. Milvexian — an oral FXIa inhibitor from Bristol Myers Squibb and Johnson & Johnson — missed its primary endpoint in its Phase II stroke trial, then saw its Phase III ACS trial fail in August 2026, narrowing the near-term competitive field. Abelacimab, a monoclonal antibody from Anthos Therapeutics that takes a different approach (inhibiting both FXI and FXIa simultaneously), is being presented at this year’s AHA sessions with positive data from the AZALEA TIMI-71 trial in atrial fibrillation. But for secondary stroke prevention specifically, asundexian is currently the furthest along in the regulatory process.

One practical gap remains for clinical adoption: no dedicated reversal agent has been approved for FXIa inhibitors. DOAC-Stop™, an activated charcoal-based adsorbent developed at McMaster University, has demonstrated the ability to reverse asundexian’s anticoagulant effect in laboratory settings, but it is not approved for clinical use. For physicians managing patients who may need emergency surgery or who experience bleeding complications, this represents an open practical question that will require resolution before broad prescribing.

A Persistent Public Health Problem

The clinical need is not abstract. Stroke kills approximately 5 million people annually worldwide and disables millions more. Globally, nearly 12 million people experience a new stroke each year. In the United States alone, approximately 795,000 strokes occur annually, of which roughly 87% are ischemic and nearly one in four is a recurrence. Despite existing antiplatelet regimens, approximately one in ten stroke survivors will suffer another stroke within a year, and roughly one in five will do so within five years.

The 2021 American Stroke Association guidelines recommend antithrombotic therapy for virtually all stroke survivors to prevent recurrence. But the available options have always required clinicians to manage a bleeding-efficacy trade-off — a constraint that has led many physicians, especially in patients with cerebral microbleeds or prior hemorrhagic stroke, to underprescribe protective therapy.

Asundexian, if FDA approval follows the Chinese precedent, would be the first anticoagulant to offer meaningful secondary stroke prevention on top of antiplatelet therapy without meaningfully increasing major bleeding. That is not an incremental advance. It is a different kind of answer to a question the field has been asking for decades — one grounded in a mechanistic insight that separates pathological clot amplification from normal wound healing.

This Afternoon

The late-breaking session runs from 1:45 to 2:45 p.m. CT today in the main event hall of the AHA Scientific Sessions at McCormick Place Convention Center in Chicago. The OCEANIC-STROKE presentation appears alongside the REDUCE trial, which examines spironolactone-based blood pressure management after stroke, and the OPTIMAL-Stroke trial on intensive blood pressure control. Together, they frame one of the most practically focused late-breaking sessions at this year’s meeting.

For the cardiology community attending the AHA’s signature gathering, today’s presentation offers something increasingly rare: a large, well-powered, positive Phase III trial that answers a question that matters, in a population that has long needed better options. The drug’s first regulatory approval has already arrived. The FDA review is under way. The science session at today’s AHA is one more step in a program that may change how noncardioembolic stroke is treated worldwide.

Asundexian (Sunharbo®) is approved in China for the prevention of ischemic stroke or TIA after a noncardioembolic event. It is investigational in the United States and has not been approved by the FDA. Approval decisions in the EU and Japan are pending. OCEANIC-STROKE (NCT05686070) was supported by Bayer AG. Investigators including Dr. Mike Sharma, Dr. Andrew Russman, and Dr. Ashkan Shoamanesh have disclosed consulting or research relationships with Bayer.

Frequently Asked Questions

What is asundexian?

Asundexian (BAY 2433334) is an oral, once-daily inhibitor of activated Factor XIa (FXIa), a protein in the intrinsic coagulation pathway. It is being developed by Bayer AG for the prevention of recurrent ischemic stroke in patients who have had a noncardioembolic stroke or high-risk TIA. As of October 26, 2026, it is approved in China under the brand name Sunharbo® and is under Priority Review by the FDA.

What is a Factor XIa inhibitor and how is it different from a blood thinner like Xarelto or Eliquis?

Traditional blood thinners (DOACs) like rivaroxaban (Xarelto) and apixaban (Eliquis) work by blocking Factor Xa or thrombin — proteins that are central to both normal wound-healing clotting and pathological thrombosis. As a result, they reduce dangerous clots but also increase bleeding risk. Asundexian targets Factor XIa, which plays a larger role in pathological arterial thrombosis than in ordinary hemostasis. The goal is to interrupt the kind of clotting that causes strokes without meaningfully impairing normal bleeding control.

What did the OCEANIC-STROKE trial find?

OCEANIC-STROKE enrolled 12,327 patients in 37 countries within 72 hours of a noncardioembolic ischemic stroke or high-risk TIA. Patients taking asundexian (plus antiplatelet therapy) had a 26% relative reduction in recurrent ischemic stroke compared to placebo (6.2% vs. 8.4%; HR 0.74; P

Has asundexian been approved anywhere?

Yes. China’s National Medical Products Administration approved asundexian (brand name Sunharbo®, 50 mg once daily) on October 26, 2026, for the prevention of ischemic stroke after a noncardioembolic stroke or TIA. The FDA is currently reviewing the application under Priority Review. The European Medicines Agency and Japan’s Ministry of Health are also reviewing submissions.

Why did asundexian fail in atrial fibrillation if it works for stroke?

In atrial fibrillation, blood stagnates in the left atrium and forms large clots through a process that depends on thrombin generation across the full coagulation pathway — both the extrinsic and intrinsic arms. FXIa inhibition blocks only the intrinsic amplification branch, which is insufficient to prevent these large stasis-driven thrombi. In noncardioembolic stroke, the thrombi are smaller and more dependent on FXIa-mediated amplification — which is why selective FXIa inhibition works in that setting but not in AF.

When might asundexian be available in the United States?

The FDA granted Priority Review, which targets a 6-month review timeline. No PDUFA (target action) date has been publicly disclosed by Bayer. Final approval depends on the FDA’s review conclusion and is not guaranteed.