Bayer and Johnson & Johnson have published data from a study which shows that the safety of their recently-approved oral anticoagulant Xarelto is comparable to warfarin in patients with atrial fibrillation.

The results of the ROCKET AF study - which appear in the New England Journal of Medicine (August 10) - show Xarelto (rivaroxaban) was equivalent to warfarin for the principal safety outcome, namely a composite of major and non-major clinically relevant bleeding.

ROCKET AF also met the primary efficacy endpoint in the study of reducing stroke and non-CNS systemic embolism at least as well as warfarin. All told, 1.7% of the Xarelto group suffered one of these clinical events compared with 2.2% of patients receiving warfarin.

While the study was not designed statistically to show superiority of Xarelto, those treated with Bayer's drug were 21% less likely to have a stroke or non-CNS embolism than those on warfarin whilst receiving treatment.

However, an editorial in the same edition of the NEJM suggests that the statistical analyses used in the study has "muddied the waters regarding rivaroxaban's efficacy and effectiveness over warfarin."

Gregory del Zoppo and Misha Eliasziw write in the editorial that ROCKET AF did not show any superiority for Xarelto on an "intent-to-treat" basis, but the authors of the study used another group of patients - the as-treated safety population - to identify a benefit for Bayer and J&J's drug.

This made interpretation of the data more difficult, they suggest, adding that warfarin was not administered as effectively in the study as it might have been. The time spent in therapeutic range for warfarin patients in ROCKET AF was just 55%, which is lower than other AF studies.

Overall, that means that Xarelto has been shown to be as good as warfarin - with the added benefits of being easier to administer and manage patients - but cannot be described as superior on the basis of the trial results, according to the editorial.

Xarelto was approved in the USA last month for the prevention of deep vein thrombosis which may lead to a pulmonary embolism in people undergoing knee or hip replacement surgery, and has also been filed for this indication in Europe.

The drug is scheduled to be reviewed by a US Food and Drug Administration panel for the prevention of stroke and systemic embolism in patients with non-valvular AF in September.