The U.S. Food and Drug Administration (FDA) has approved Bayer’s Sunharbo (asundexian), a once-daily oral medicine designed to reduce the risk of another stroke in certain adults who have recently experienced an ischemic stroke or high-risk transient ischemic attack (TIA). The November 9, 2026, decision makes Sunharbo the first factor XIa inhibitor approved in the United States, introducing a new class of treatment for secondary stroke prevention.
The medicine is approved for use alongside antiplatelet therapy in adults who have experienced a recent mild-to-moderate non-cardioembolic ischemic stroke or a high-risk TIA. Its approval is based on the Phase 3 OCEANIC-STROKE clinical trial, which found that patients receiving asundexian had a 26% lower risk of ischemic stroke than those receiving a placebo over a median treatment period of 14.2 months. The results also showed a broadly similar overall rate of major bleeding, although certain patient groups experienced higher bleeding rates.
FDA Approves Sunharbo for Secondary Stroke Prevention
Sunharbo contains asundexian, an oral inhibitor of factor XIa, a protein involved in the blood-clotting process. Bayer developed the medicine to reduce the formation of harmful blood clots while having a more limited effect on the body’s normal ability to stop bleeding.
The FDA approved the 50-milligram tablet for adults following a recent non-cardioembolic ischemic stroke with a National Institutes of Health Stroke Scale score of 15 or lower, or a high-risk TIA. The recommended dose is 50 mg once daily, in combination with antiplatelet therapy.
A non-cardioembolic ischemic stroke occurs when a blood clot blocks blood flow to the brain but does not originate in the heart. A TIA, sometimes called a mini-stroke, involves temporary symptoms caused by disrupted blood flow and can signal an increased risk of a subsequent stroke.
The approval does not cover stroke prevention in people with atrial fibrillation. It also does not mean that Sunharbo can replace existing antiplatelet medicines or other treatments prescribed after a stroke.
How Factor XIa Inhibition Works
Factor XIa is part of the body’s coagulation system, which helps blood form clots. When this protein becomes active, it contributes to the amplification of thrombin generation, a process that supports clot formation.
Sunharbo works by inhibiting factor XIa. The approach is based on the possibility of reducing pathological clotting while preserving more of the normal clotting response needed to prevent excessive bleeding.
This distinction is important because medicines that prevent blood clots can also increase bleeding risk. Existing antiplatelet and anticoagulant treatments are widely used to prevent recurrent cardiovascular events, but their benefits must be balanced against potential bleeding complications.
Factor XIa inhibitors are being developed to offer another way of managing this balance. Sunharbo’s approval provides the first U.S. regulatory validation of this approach for a specific stroke-prevention population.
Phase 3 OCEANIC-STROKE Trial Demonstrated a 26% Reduction
The FDA’s decision was supported by OCEANIC-STROKE, a randomized, double-blind, placebo-controlled Phase 3 study involving 12,327 adults.
Participants had experienced a recent non-cardioembolic ischemic stroke or high-risk TIA. They were assigned to receive either Sunharbo or a placebo within 72 hours of the qualifying event. Both groups also received antiplatelet therapy.
The primary efficacy measure was the time until the first occurrence of an ischemic stroke.
| Trial measure | Sunharbo | Placebo |
|---|---|---|
| Participants | 6,162 | 6,165 |
| Ischemic stroke incidence | 6.2% | 8.4% |
| Major bleeding rate per 100 patient-years | 1.6 | 1.5 |
| Median treatment duration | 14.2 months | 14.2 months |
The incidence of ischemic stroke was 6.2% among patients receiving asundexian, compared with 8.4% in the placebo group. This represented a 26% relative reduction in risk.
The trial also reported a reduction in the occurrence of all strokes, including ischemic and hemorrhagic events. The combined outcome of cardiovascular death, heart attack or stroke was also lower in the Sunharbo group, although the reported improvement was primarily driven by the reduction in ischemic strokes.
The findings were published in the New England Journal of Medicine in 2026.
Bleeding Risks and Other Safety Considerations
Although the overall rate of major bleeding was similar between the treatment and placebo groups, the safety findings require careful interpretation.
Bayer’s prescribing information reports that major bleeding rates were higher among patients older than 75 years and during the first 90 days of treatment. Gastrointestinal bleeding was also more frequent in the Sunharbo group.
Diarrhea was the most frequently reported adverse reaction occurring in more than 3% of patients treated with the medicine. The FDA also highlighted several precautions involving other medicines and medical procedures.
Key considerations include:
- Older patients: Major bleeding rates were higher among participants older than 75 years receiving Sunharbo.
- Gastrointestinal bleeding: The rate was higher in the treatment group than in the placebo group.
- Drug interactions: Combining Sunharbo with medicines that are both P-glycoprotein and strong CYP3A4 inducers, such as carbamazepine, is not recommended because they may reduce the medicine’s effectiveness.
- Liver impairment: The medicine is not recommended for patients with moderate or severe hepatic impairment.
- Surgery and procedures: Sunharbo should be withheld at least 24 hours before elective surgery or invasive procedures.
- Thrombolysis: The medicine should be withheld for at least 24 hours after thrombolysis for acute ischemic stroke.
These considerations mean that treatment decisions will need to account for a patient’s medical history, existing medicines and individual bleeding risk.
Why the Approval Matters for Bayer and the Pharmaceutical Industry
The approval gives Bayer an important position in the emerging factor XIa inhibitor market. Sunharbo is the first medicine in this class to receive U.S. approval, potentially establishing a regulatory and clinical benchmark for other pharmaceutical companies developing similar treatments.
The factor XIa mechanism has attracted interest because researchers are looking for ways to prevent dangerous blood clots without substantially increasing bleeding complications.
However, the development of this drug class has faced setbacks. Bayer previously discontinued a Phase 3 study of asundexian in patients with atrial fibrillation after the medicine did not demonstrate the required effectiveness compared with apixaban. The new approval is therefore limited to a different population: people with non-cardioembolic ischemic stroke or high-risk TIA.
The distinction is important. Success in secondary prevention following a non-cardioembolic stroke does not establish that the medicine is effective for every condition associated with blood clots.
Bayer said it expected Sunharbo shipments to begin in the United States in mid-to-late November 2026. The company also reported that the medicine had received approval in China in October 2026, while regulatory reviews in Europe and Japan were ongoing at the time of its announcement.
The Bigger Picture
Sunharbo’s approval represents a new development in stroke prevention, an area where reducing the risk of another event is a major priority for patients and healthcare providers. The trial results suggest that factor XIa inhibition can provide an additional option for eligible patients when used alongside established antiplatelet treatment.
The decision also demonstrates how pharmaceutical research is moving beyond traditional approaches to blood-clot prevention. If further evidence supports the benefits and safety of factor XIa inhibitors, the drug class could become increasingly important in cardiovascular and cerebrovascular medicine.
Looking Ahead
The next phase for Sunharbo will involve its introduction into clinical practice and continued evaluation of its safety and effectiveness in eligible patients. Doctors will need to consider the medicine’s bleeding profile, potential interactions and the specific circumstances of each patient before prescribing it.
For Bayer, the FDA approval provides an opportunity to establish the first commercial product in a new category of stroke-prevention medicines. The longer-term impact will depend on real-world clinical experience, additional research and whether competing factor XIa treatments can demonstrate similar or improved outcomes.
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