An experimental blood thinning drug made by the pharmaceutical giant Merck may reduce the risk of dying from a heart attack but also boosts the danger of internal bleeding, researchers said Saturday.
The latest data further clouds the future for Vorapaxar, an anti-platelet medicine that works differently than aspirin or the popular blood thinner coumadin, and which Merck had hoped might one day be a new blockbuster drug.
Vorapaxar was tested in combination with standard therapy in a phase III trial presented at a major cardiology conference in Chicago.
Adding the drug could reduce the risk of dying from a future heart attack or stroke by as much as 20 percent in people who had a previous heart attack, but it also significantly hiked the risk of hemorrhage, the study said.
While heart attack patients showed the best results, among all the patients studied -- including those with a prior history of stroke or peripheral artery disease -- the drug offered an additional 13 percent reduction in the risk of dying from a heart attack or stroke within three years.
However, patients in the trial who suffered a previous stroke and took vorapaxar had significantly more hemorrhage events after three years -- 4.2 percent of those on the drug versus 2.5 percent taking a placebo.
The risk of bleeding on the brain was highest in prior stroke victims, meaning that if approved for market the drug would not likely be advised for these patients.
In fact, stroke patients involved with the Merck-funded study were told in January 2011 to leave early by the safety board after the acute risks emerged.
"Of the groups we studied, the benefit was compelling to us only in patients with a prior heart attack," said a statement by lead investigator David Morrow, director of the Samuel A. Levine Cardiac Unit at Brigham & Women's Hospital.
Vorapaxar is part of a new class of investigational platelet blocker drugs known as thrombin receptor antagonists, which stop a process that normally allows the blood's platelets to stick together and form clots.
"In the lab, we have seen very compelling science showing the importance of thrombin's action on platelets causing blood clots in arteries," added Morrow.
"This is the first study to show definitively that blocking this pathway reduces the risk of suffering another cardiovascular event."
The randomized, multinational study followed 26,449 patients for more than two years. Its results were presented at the American College of Cardiology Conference and published simultaneously in the New England Journal of Medicine.
Merck said it was in discussions about the latest study results and would consult with the investigators and outside experts to determine the path forward.
Explore further: TARDIS trial seeks new dimension in stroke treatment