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* Risk of brain hemorrhage tripled for vorapaxar-study
* Lower incidence of heart attack seen with Merck drug
* Vorapaxar hopes already were dimmed from January setback
* Merck says to wait for 2nd study before deciding on drug
By Lewis Krauskopf and Bill Berkrot
ORLANDO, Fla., Nov 13 (Reuters) - An experimental anti-clotting drug from Merck & Co failed to meet the main goal of of improving a host of cardiovascular problems in a large study and tripled the risk of bleeding in the brain, researchers said on Sunday.
The prospects for vorapaxar had already been severely dented after a safety committee overseeing this and another large study of the drug in January said it was not appropriate in patients who had suffered a stroke, due to excess bleeding.
While Wall Street analysts had largely written off vorapaxar, once seen as possibly generating $3 billion in annual sales, there were hopes the Tracer study results presented on Sunday could somewhat revive the product.
Patients on vorapaxar did see a lower incidence of heart attacks, according to the results presented at the American Heart Association scientific sessions in Orlando, and Merck said it was still awaiting results from the second study, due early next year, before making any decisions on the medicine's future.
"There is a signal of efficacy with vorapaxar driven primarily by" a reduction in heart attacks, said Dr. Kenneth Mahaffey, one of the study's lead investigators. He called the reduction intriguing, "but when you balance it with the bleeding then it becomes a little less impressive."
Vorapaxar was considered the most important drug in Schering-Plough's experimental drug pipeline when Merck acquired its rival for $41 billion in late 2009.
The primary goal of the Tracer study was a reduction in a combination of cardiovascular death, heart attack, stroke, hospitalization for chest pain and need for artery clearing procedures.
After two years, 18.5 percent of patients on vorapaxar and 19.9 percent of patients who received a placebo had suffered one of those adverse events. The 8 percent relative difference was not considered to be statistically significant. All patients in the study were already on standard blood thinners, primarily aspirin and Plavix or just aspirin.
A secondary goal of the study looked at just cardiac death, heart attack and stroke, and by that measure vorapaxar came out looking better. In vorapaxar patients, 14.7 percent had such an event compared with 16.4 percent for placebo, primarily due to a difference in heart attacks. There was no difference in death and only a modest difference in stroke, researchers said.
Bleeding rates were nearly 40 percent higher in vorapaxar patients, and there was a three-fold increase in intracranial hemorrhage.
"The magnitude of the excess of bleeding was quite unexpected" based on previous studies, Mahaffey said. The bleeding risk also increased over time for vorapaxar, researchers said.
Mahaffey did not believe the trial's failure meant the end for vorapaxar or the class of anti-platelet drugs known as PAR 1 inhibitors.
"Clearly the bleeding needs to be understood more," he said.