Bristol-Myers Squibb and Pfizer have received a major boost with the news that their experimental bloodthinner Eliquis has come through a late-stage trial very successfully.

The two US companies have announced top-line results from the Phase III ARISTOTLE trial of Eliquis (apixaban) in patients with atrial fibrillation and at least one additional risk factor for stroke. The drug met the primary efficacy objective of non-inferiority to warfarin on the combined outcome of stroke and systemic embolism.

Pfizer and B-MS added that Eliquis, a twice-daily oral direct Factor Xa inhibitor, met the key secondary endpoints of superiority on efficacy and also led to less bleeding compared to warfarin. The companies expect to submit regulatory filings in AF in the USA and Europe in the third or fourth quarter of 2011.

The detailed results of the study will be presented at the European Society of Cardiology congress in Paris at the end of August. The full data set will be eagerly anticipated given that some analysts believe Eliquis could become the drug of choice in the huge stroke market.

At the moment, its principal rival will be Boehringer Ingelheim's already-approved twice-daily oral direct thrombin inhibitor Pradaxa (dabigatran etexilate), which has got off to a terrific start in the USA. The next entrant in the market is likely to be Bayer/Johnson & Johnson's once-daily Factor Xa inhibitor Xarelto (rivaraxoban), although studies have shown that the latter failed to beat warfarin on either efficacy or safety, but rather demonstrated equivalence.

The response to the apixaban top-line data from analysts has been one of excitement. Marc Goodman at UBS issued a research note saying that “we see these results are the best outcome possible given that expectations did not include superior efficacy”. He added that “given the headline profile, apixaban could have a superior label to Pradaxa, which is only superior on efficacy, and should have a better label than Xarelto.”

Shares in Pfizer and B-MS are expected to rise considerably once the markets open later today in the USA, while in Europe, Bayer's stock was down 5.5% at 54.82 euros at 10.15am (UK time).