Study of experimental blood thinner halted prematurely

Pfizer Inc. and Bristol-Myers Squibb said late Thursday that they were terminating a study of the experimental blood thinner apixaban prematurely because the drug was showing no benefits and was producing excess bleeding among patients receiving it. The study, called APPRAISE-2, was testing the drug in 10,800 patients with acute coronary syndrome, a group of problems characterized by chest pain caused by insufficient blood supply to the heart muscle. The company said it would also stop a similar study in Japan.

APPRAISE-2 is one of nine studies of the highly promising drug now underway. Apixaban, which inhibits blood clotting by blocking factor Xa, is meant to be a replacement for the widely used anticoagulant warfarin. It belongs to the same family of drugs as rivaroxaban, which was reported earlier this week to be at least as good as warfarin at preventing strokes in patients with atrial fibrillation. The two companies had halted a trial of the drug in patients with atrial fibrillation in August when the drug was found to be superior to aspirin in treating patients with atrial fibrillation who could not tolerate warfarin.

Companies are eager to find replacements for warfarin because patients must undergo monthly blood tests to ensure that they have a therapeutic dose in their bloodstream, and certain foods containing vitamin K can block the drug’s activity.

The company said it remained committed to developing apixaban for other purposes.