A Bayer medication that uses a new approach to preventing blood clots has received FDA approval, making it the first-in-class treatment for patients who have had a stroke.
The drug, asundexian, is a new secondary stroke prevention therapy designed to lower risk after an initial event. The late Monday announcement covers adults who recently had a stroke caused by a clot that did not originate in the heart, as well as those who experienced a high-risk transient ischemic attack, often called a “mini-stroke.” Bayer said its once-daily pill will launch in mid-November under the brand name Sunharbo.
Blood thinners have long been standard for secondary stroke prevention, but they carry a higher risk of bleeding, especially with long-term use. Sunharbo targets a different pathway. The small molecule is designed to block Factor XIa, reducing the generation of thrombin, an enzyme involved in blood clot formation.
In the Phase 3 trial, the study drug was evaluated alongside standard antiplatelet therapies. Results showed a 26% reduction in the risk of stroke of any kind compared with a placebo and antiplatelet therapy cohort. The reduction occurred without increasing bleeding rates, which were comparable between groups. The most frequently reported adverse reaction among patients receiving the study drug was diarrhea. Detailed trial results were presented last February at the International Stroke Conference and published in April in the New England Journal of Medicine.
Sunharbo was discovered and developed internally by Bayer. Although the German pharmaceutical company will be first to market with a Factor XIa inhibitor, competition is expected. Bayer’s partners Bristol Myers Squibb and Johnson & Johnson are pursuing the target with a small molecule called milvexian; Phase 3 data in secondary stroke prevention are expected by the end of this year.
Milvexian is a twice-daily pill. In an October research note, Leerink Partners analyst David Risinger said the less convenient dosing means the drug will need to achieve greater than 30% stroke risk reduction—more than Sunharbo’s 26%—to justify adoption. Milvexian is also being studied for atrial fibrillation, a larger indication. Sunharbo did not succeed in a Phase 3 trial in atrial fibrillation three years ago. Bayer executives have said the drug could be developed for other conditions, but specific indications of interest have not yet been disclosed.
In a conference call last week to discuss Bayer’s third-quarter 2026 financial results, Stefan Oelrich, head of the company’s pharmaceuticals division, acknowledged potential competition from milvexian. He noted, however, that Sunharbo has about a year’s head start and that it has clinical data supporting differentiation.
“Obviously, we believe that we have an extremely solid data set when it comes to secondary stroke prevention, where I think whoever comes there will come up with something really, really good if they want to beat us,” Oelrich said.
Other contenders pursuing Factor XI for secondary stroke prevention have turned to different drug modalities. Novartis’s Factor XI inhibitor is an antibody, while newly public ADARx Pharmaceuticals is developing a small interfering RNA therapy.
China was the first country to approve Sunharbo, a regulatory decision issued late last month. The drug is still under review in Europe and Japan.
