The US Food and Drug Administration has approved asundexian, sold as Sunharbo, the first drug to block clotting factor XIa. In a trial of more than 12,000 patients, adding it to standard antiplatelet therapy after a stroke cut recurrent ischaemic strokes by about a quarter, without a significant overall increase in major bleeding. That combination has eluded anticoagulant drugs for decades. Important cautions apply to older patients, and it is not approved for atrial fibrillation.
After a first ischaemic stroke, the risk of another is highest in the weeks and months that follow. Doctors have long faced a dilemma. Antiplatelet drugs such as aspirin and clopidogrel reduce that risk only partly. Stronger anticoagulants, which act on the clotting cascade, prevent more clots but cause more bleeding, including bleeding into the brain. For patients whose stroke was not caused by atrial fibrillation, adding a conventional anticoagulant has not been worth the trade-off.
On 9 November, the FDA approved a drug designed to break that trade-off. Asundexian, developed by Bayer and marketed as Sunharbo, is a 50 mg tablet taken once daily alongside antiplatelet therapy. It is for adults who have had a recent mild-to-moderate non-cardioembolic ischaemic stroke or a high-risk transient ischaemic attack (TIA). The FDA called it “a meaningful advance for patients and health care providers”, in the words of Hylton Joffe of its Center for Drug Evaluation and Research. It is the first approved drug of its class.
How it works
Blood clotting involves a cascade of proteins, or clotting factors, each activating the next. Existing anticoagulants such as warfarin, apixaban and rivaroxaban act on factors that are central to all clotting, including the clotting that seals a wound. That is why they cause bleeding.
Factor XI sits higher in what is called the intrinsic pathway. People born with factor XI deficiency rarely suffer spontaneous serious bleeding, and appear to be protected against strokes and venous clots. That observation suggested that blocking factor XI, or its active form XIa, might prevent harmful clots while largely sparing normal haemostasis. Asundexian is a small molecule that inhibits factor XIa.
The evidence: OCEANIC-STROKE
The approval rests on OCEANIC-STROKE, a phase 3, double-blind, placebo-controlled trial published in the New England Journal of Medicine (lead author Mike Sharma of McMaster University). It was first presented at the International Stroke Conference in February 2026.
- Patients: 12,327 people at 702 centres in 37 countries, randomised within 72 hours of a mild-to-moderate ischaemic stroke or high-risk TIA. All also received antiplatelet therapy. Median treatment lasted 14.2 months.
- Efficacy: ischaemic stroke recurred in 6.2% of patients on asundexian and 8.4% on placebo (hazard ratio 0.74; 95% confidence interval 0.65–0.84; P<0.001). Disabling or fatal strokes fell from 3.0% to 2.1%.
- Safety: major bleeding (by International Society on Thrombosis and Haemostasis criteria) occurred in 1.9% against 1.7%, a difference that was not statistically significant (HR 1.10; 0.85–1.44). Serious adverse events were similar, at 19.2% and 19.5%. Diarrhoea was the most common side-effect.
“The curves diverged early, and that divergence continued throughout the treatment period,” Sharma said. At one year, the absolute reduction in stroke risk was about 1.9 percentage points: roughly 53 patients would need to be treated for a year to prevent one stroke. At 90 days, the difference was not yet statistically significant.
The cautions
The FDA’s label carries important warnings:
- Older patients: the risk of major bleeding was higher in patients over 75.
- Timing: bleeding risk was also higher in the first 90 days of treatment.
- Gastrointestinal bleeding: more common than with placebo.
- Interactions and liver disease: avoid with drugs that strongly induce the P-glycoprotein and CYP3A4 systems, and in moderate or severe liver impairment.
- Procedures and thrombolysis: the drug should be stopped for 24 hours before procedures and after clot-busting treatment.
It is not approved for atrial fibrillation. In an earlier trial in that condition, asundexian was less effective than apixaban, and that study was stopped.
There are other limitations. The trial was sponsored by Bayer. It excluded patients whose strokes came from the heart, as well as patients on dialysis. The long-term benefits beyond the trial period are unknown. In the United States, the list price is about US$748.50 for 30 days, according to BioPharma Dive.
What clinicians say
Specialists not involved in the trial have welcomed the result. “Very groundbreaking for us clinicians who take care of stroke patients,” Richa Sharma, a stroke neurologist at Yale, said in coverage of the approval. Bayer’s chief operating officer, Sebastian Guth, said physicians see the drug as “practice-changing”. That is a company view, and practice will depend on how guideline committees weigh the bleeding warnings for older patients.
In the trial, patients were enrolled after strokes scored up to 15 on the National Institutes of Health Stroke Scale, which covers mild-to-moderate deficits, or after a TIA judged high-risk. The drug is meant to be added to, not substituted for, the antiplatelet treatment such patients already receive. In practice, that means aspirin, clopidogrel or, for a short period after a minor stroke, both together.
A crowded field
Asundexian is first, but not alone. Bristol Myers Squibb and Johnson & Johnson’s milvexian, another factor XIa inhibitor, has had mixed results. Novartis paid US$925 million up front to acquire Anthos Therapeutics and its anti-factor XI antibody, and RNA-based drugs are in development. China approved asundexian before the United States, as Bayer announced on 26 October. For Bayer, the drug matters commercially as well: sales of its anticoagulant Xarelto fell by about 43% in the first half of 2026, to €738 million, as generic competition arrived, according to BioPharma Dive.
Relevance to India
Stroke is among the leading causes of death and long-term disability in India. A drug that reduces recurrence without much extra bleeding would therefore be valuable. NSH found no Indian regulatory filing, and has not verified whether Indian centres took part in the trial. Any Indian approval would require review by the Central Drugs Standard Control Organisation (CDSCO). Price will be a decisive factor.
