Researchers reported Sunday that atrial fibrillation patients who received Bayer’s experimental anticoagulant were significantly more likely to experience a stroke or systemic embolism compared to those who got Eliquis.
The company in November announced that it stopped its 14,810-person OCEANIC-AF study early due to asundexian’s inferior efficacy, a concerning result for what Bayer called a landmark clinical trial program.
In the Phase 3 clinical trial, 98 patients who received asundexian had a stroke or systemic embolism compared to 26 in the control arm who got the anticoagulant Eliquis, also known as apixaban. That resulted in a hazard ratio of 3.79 — an outcome that no drug developer ever wants to see.
Atrial fibrillation is a type of irregular and often fast heartbeat. People with atrial fibrillation take anticoagulants as a form of stroke prevention, but the currently marketed anticoagulants — direct-acting oral anticoagulants, or DOACs — come with a risk of bleeding. Bayer and other drug companies have now turned to a class of experimental treatments called factor XI inhibitors, which they hope could provide the same level of stroke and blood clot prevention without the bleeding risk.
On the safety front, 17 patients experienced major bleeds on asundexian compared to 53 on Eliquis.
Johnson & Johnson and Bristol Myers Squibb are developing a factor XI inhibitor called milvexian and have put together a similarly massive clinical trial program. Meanwhile, Novartis and Blackstone-backed Anthos Therapeutics are developing a once-monthly antibody treatment also targeted at factor XI. Both are in late-stage trials.
Searching for explanations
The OCEANIC-AF trial results were shared at the European Society of Cardiology’s annual meeting and published in the New England Journal of Medicine.
The co-authors of the NEJM study, led by Duke professor of medicine Jonathan Piccini, floated several possibilities as to why asundexian led to higher levels of stroke or blood clots compared to Eliquis.
They started with the most straightforward explanation, writing that “it is possible that factor XIa inhibition with asundexian does not lead to effective stroke prevention as compared with apixaban in patients with atrial fibrillation.”
The study authors also suggested that “escape mechanisms may play an important role, especially in patients with atrial fibrillation being transitioned from ongoing oral anticoagulation.” The basis for targeting factor XI comes from data that show people with natural factor XI deficiency may have a lower risk for stroke and blood clots.
Another potential explanation was that the once-daily 50 mg of asundexian is not a high enough dose. In a Phase 2 trial, the 50 mg dose led to a 92% to 94% reduction in factor XI activity, but perhaps “complete or near complete (>99%) suppression of factor XIa may be required,” the researchers wrote.
They concluded by adding that the incidence of stroke in the control arm was significantly lower than predicted or seen in the key trial behind Eliquis’ approval over a decade ago.
“The findings of the OCEANIC-AF trial are probably attributable to a combination of these factors,” the study authors wrote.
Bayer is running a separate Phase 3 study called OCEANIC-STROKE, but announced in November it is reevaluating plans for a third Phase 3 study called OCEANIC-AFINA.