Bayer has won U.S. Food and Drug Administration approval for Sunharbo, a once-daily 50 mg tablet that becomes the first factor XIa inhibitor (a drug blocking a blood-clotting protein) cleared to reduce the risk of a second stroke. The FDA announced the decision on Monday.

The approval covers adults who recently suffered a mild-to-moderate non-cardioembolic ischemic stroke — a clot-caused stroke that did not originate in the heart — or a high-risk transient ischemic attack (a temporary blockage of blood flow to the brain). Sunharbo must be used together with antiplatelet therapy, drugs that prevent blood cells from clumping. The FDA did not approve the drug for stroke prevention in patients with atrial fibrillation, an irregular heartbeat.

What did the trial show?

The decision rests on OCEANIC-STROKE, a placebo-controlled phase 3 trial of 12,327 adults, all of whom received antiplatelet therapy. Sunharbo reduced the risk of ischemic stroke by 26% over a median treatment period of 14.2 months, the FDA said.

A second stroke occurred in 6.2% of patients taking Sunharbo, against 8.4% of those on placebo, according to STAT.

The rate of major bleeding was comparable between the two groups, the FDA said. The safety picture carries caveats:

• Bleeding increased among patients older than 75 and during the first 90 days of treatment.
• Gastrointestinal bleeding was more common with Sunharbo.
• Diarrhea was the most frequent adverse reaction, occurring in 3% or more of patients.

The FDA advises against prescribing Sunharbo alongside medicines that are combined P-gp and strong CYP3A4 inducers (drugs that speed the breakdown of other medicines), such as carbamazepine, or in patients with moderate or severe hepatic impairment, meaning reduced liver function. Physicians should withhold the drug for at least 24 hours before elective surgery or invasive procedures.

Who is behind the decision?

"Stroke is a leading cause of disability and death in the United States, and survivors are at risk of having another stroke," Hylton V. Joffe, director of the Office of Cardiology, Hematology, Endocrinology, and Nephrology in the FDA's Center for Drug Evaluation and Research, said in a statement.

Sunharbo blocks Factor XIa, a blood-clotting protein, and represents a novel type of anticoagulant, according to BioPharma Dive. A 30-day supply is listed at $748.50.

What does this mean for Bayer?

Sebastian Guth, Bayer U.S. president and chief operating officer of Bayer Pharmaceuticals, said stroke neurologists will be a "very important part" of the early rollout, according to BioPharma Dive.

Bayer stock gained up to 2% during opening hours of Frankfurt trading on Tuesday. China approved the drug in late October, according to Bloomberg, giving Bayer two major markets inside roughly a month.

The launch arrives as Bayer's pharmaceutical unit contends with generic rivals to two of its biggest products: the Xarelto anticoagulant and the Eylea eye treatment. Sunharbo, with its novel mechanism and a 26% risk reduction, gives the company a first-mover position in the factor XIa class.

That lead may not last. Bristol Myers Squibb and Johnson & Johnson have a comparable candidate, milvexian, in trials, setting up a race to capture the market for safer anticoagulation in stroke survivors.

For now, Bayer holds the only approved factor XIa inhibitor in the United States, a $748.50-per-month therapy aimed at thousands of patients at risk of a second clot-driven stroke.