New Anti-Clotting Medication Shows Promise in Preventing Second Strokes Without Bleeding Risk

An investigational anti-clotting medication, asundexian, demonstrated a reduction in the risk of a second ischemic stroke without raising bleeding concerns, according to preliminary findings presented at the American Stroke Association’s International Stroke Conference 2026. The research represents the first completed trial of a Factor XI inhibitor investigating whether this new class of medication is better than standard therapy at safely preventing recurrent strokes. When added to standard blood-thinning medications such as aspirin, asundexian reduced the risk of a second stroke by reducing the formation of blood clots without increasing the risk of bleeding.

According to the American Stroke Association, a division of the American Heart Association, nearly 1 in 4 stroke survivors will have another stroke, called a secondary stroke. The 2021 guideline from the American Stroke Association states that antithrombotic therapy, including antiplatelet or anticoagulant agents, is recommended for nearly all stroke survivors to prevent a second stroke. However, current antiplatelet therapy has limited effectiveness in preventing recurrent stroke because of bleeding risks. Previous efforts to improve outcomes by adding other anticlotting or blood thinning medications have not succeeded due to increased risk of bleeding, lack of benefit, or both.

Asundexian is a novel investigational medication that inhibits a clotting protein called Factor XI, which is involved in producing large blood clots that can block blood vessels. Unlike other anticoagulants that inhibit a different clotting protein to reduce stroke risk, asundexian does not increase bleeding risk. People born with a genetic deficiency of Factor XI are known to have a lower risk of ischemic stroke and rarely have spontaneous bleeding. This research, the OCEANIC-STROKE study, is a Phase III international trial that included more than 12,300 stroke survivors investigating whether adding daily asundexian to antiplatelet therapy could reduce the risk of a new stroke caused by a blood clot without increasing bleeding or other adverse events.

Participants were randomly selected to receive either standard antiplatelet therapy plus a daily dose of asundexian or standard antiplatelet therapy plus a placebo. Neither patients nor researchers were aware of which treatment they received during the trial. Participants were followed for 3 to 31 months, and researchers found that compared to a placebo, adding asundexian to antiplatelet medication reduced the occurrence of ischemic stroke by 26%, and this reduction was consistent for all participants regardless of several key factors: age or sex, the cause of stroke, or the severity of the first stroke. The treatment also reduced the occurrence of a disabling stroke, did not increase bleeding within the brain or major bleeding, did not increase serious adverse effects, and lowered cardiovascular death, stroke of any type, heart attack, and major bleeding, indicating an overall benefit to patients.

The study was conducted at 702 sites in 37 countries, with participants enrolled between January 2023 and February 2025. The participants were enrolled within 72 hours of a mild-to-moderate ischemic stroke or a transient ischemic attack deemed to represent a high risk of a more severe stroke. None of the participants had atrial fibrillation, an artificial heart valve, or other conditions that can lead to a blood clot that travels from the heart to the brain to cause a stroke. Participants were randomly chosen to receive either 50 mg/day of asundexian or a placebo in addition to standard antiplatelet therapy. They were monitored for a minimum of 3 months and up to 31 months for the occurrence of ischemic stroke or major bleeding as defined by the International Society on Thrombosis and Hemostasis.

Asundexian is an investigational medication that has not been approved in any country. The U.S. Food and Drug Administration has granted the medication fast-track designation for its potential use in stroke prevention after ischemic stroke not caused by a blood clot originating in the heart. If approved, asundexian could be widely used for patients who have had a non-cardioembolic stroke or a TIA. The study is limited by having relatively few participants with severe strokes, despite broad inclusion criteria that could have included them. In a substudy of OCEANIC-STROKE, brain imaging and standardized MRI images were collected for participants, with analysis of that data not yet complete. Bayer, who manufactures asundexian, funded the study and provided the medication and placebo used in the trial. Additional information about stroke prevention is available through the American Stroke Association at https://www.stroke.org.