Bristol-Myers Squibb and Pfizer's apixaban failed to significantly help seriously ill patients cut their risk of dangerous blood clots, according to clinical data released on Sunday.   

The drug showed a trend toward cutting the clots, but the difference compared with patients taking an older medicine was not statistically significant, researchers said.

Apixaban also caused a higher rate of dangerous bleeding, although there was no incidence of fatal bleeding, according to the Adopt study data presented at the American Heart Association scientific sessions in Orlando.   

"Apixaban essentially comes pretty close to proof of principle," said Dr Samuel Goldhaber, the study's lead investigator.

He said a very high number of patients who dropped out of the study and the use of the older comparative drug enoxaparin for longer than is common in medical practice may have contributed to apixaban's inability to hit the trial's main goal.

Hopes were low for apixaban to succeed in this particularly high-risk group of hospitalized patients, especially after Xarelto, a rival pill from Johnson & Johnson and Bayer AG, showed a surprisingly high rate of bleeding in this use in data released in April.

Strong results could have aided apixaban as it prepares to battle for market share with Xarelto and another new blood clot medicine, Pradaxa, from privately held Boehringer Ingelheim.

Apixaban and Xarelto belong to a class called Factor Xa inhibitors, named for blocking a protein involved in the blood clotting process, while Pradaxa is a direct thrombin inhibitor.

Apixaban, also known as Eliquis, has demonstrated impressive efficacy and safety in preventing stroke for patients with atrial fibrillation, or dangerously irregular heart rhythms, making it the likely leader in that estimated $10 billion market should it win approval for that use.
   
The companies have said they plan to apply for U.S. and European approval for stroke prevention use by the end of the year.

Patients in the Adopt study were suffering from a variety of serious illnesses and deemed at high risk of developing dangerous blood clots such as deep vein thrombosis and pulmonary embolism, the latter of which occurs when a clot breaks off and gets caught in the lung, which can be fatal.

Collectively known as venous thromboembolism (VTE), the clots affect 300,000 to 600,000 Americans each year, according to the Centers for Disease Control and Prevention.   

Admission to the hospital for a medical illness puts a person at a tenfold increased risk for developing VTE, according to Brigham and Women's Hospital in Boston.

Goldhaber said that VTE risk can increase once a patient is released from the hospital. He said the difference in adverse events clearly began to favor apixaban following hospitalization, and after patients stopped enoxaparin injections, suggesting that the trial might have been more successful if the pill was taken for more than 30 days.

The Adopt study included 6,528 patients who had been hospitalized for at least three days for congestive heart failure, acute respiratory failure, or other serious conditions with VTE risk factors.  - Reuters