Bristol-Myers Squibb and partner Pfizer are stopping a late-stage study of their investigational anticoagulant apixaban after data showed that the drug prevented stroke among patients with atrial fibrillation.

The major Phase III study, called AVERROES, involved 5,600 patients with AF at risk for stroke who were considered intolerant of or unsuitable for therapy with a vitamin K antagonist such as warfarin. Patients were randomised to receive either apixaban 5mg twice daily or aspirin 81mg-324 mg once daily. The trial is being halted because a predefined interim analysis by the independent data monitoring committee “revealed clear evidence of a clinically important reduction in stroke and systemic embolism” in AF patients.

The companies added that the analysis also demonstrated an acceptable safety profile for apixaban compared to aspirin. The drug is being tested in nearly 60,000 patients worldwide in a programme that includes nine completed or ongoing Phase III trials.

Apixaban is being evaluated for the prevention of venous thromboembolism, stroke and other thromboembolic events in patients with AF, as well as for the treatment of VTE and secondary prevention of cardiovascular events in patients with acute coronary syndrome. Preventing stroke in AF patients is widely perceived as the most lucrative of the possible indications.

If approval is achieved, possibly in 2012, apixaban will go up against Boehringer Ingelheim’s Pradaxa (dabigatran etexilate) and Bayer/Johnson & Johnson's Xarelto (rivaroxaban).