Vorapaxar TRACER study halted after safety review

Kathleen Blanchard's picture
Vorapaxar trial halted from increase bleeding risk.

The drug vorapaxar was shown to increase the risk of bleeding in patients with acute coronary syndrome (ACS), resulting in an end to the TRACER study. The drug, designed by Merck, blocks blood clots by inhibiting platelet activation, but was found to lead to major bleeding in patients taking concurrent antiplatelet therapy.

Results of the TRACER study, which included 12,944 patients with ACS, improved cardiovascular outcomes for patients with heart attack.

Compared to placebo, 8.5% of patients in the vorapaxar group versus 19.9% in the placebo group died or were rehospitalized with MI, stroke, recurrent ischemia or urgent coronary revascularization.

But patients in the TRACER study taking vorapaxar were more likely to experience intracranial hemorrhage (1.1%), compared to participants given placebo (0.2%).

Death rates among patients receiving vorapaxar were lower, however, compared to placebo - 14.7 percent for the group receiving the antiplatelet therapy, versus 16.4% receiving placebo.

A concurrent study, TRA-2P TIMI 50, will continue, using vorapaxar for secondary prevention. The study includes patients with a history of peripheral artery disease (PAD), stroke or heart attack.

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Results of TRACER were presented during the late-breaking clinical trials session at the American Heart Association (AHA) 2011 Scientific Sessions, and are published online in the New England Journal of Medicine.

"Because most patients in TRACER had vorapaxar added to a regimen containing both a P2Y12 inhibitor and aspirin, we now better understand the effect of using these three mechanisms together to prevent clots in patients with ACS," said Peter S. Kim, Ph.D., executive vice president, Merck and president, Merck Research Laboratories.

"Fewer patients in TRA-2P were taking both aspirin and a P2Y12 inhibitor, so the results from the second vorapaxar study should give us greater insight into the effect of blocking PAR-1 in different groups of patients, including many patients who were not taking the combination of a P2Y12 inhibitor and aspirin."

Patients who were not taking aspirin were not at increased risk of bleeding in the TRACER study.

Results of TRA-2P will be presented for publication in early 2012. Patients in the study with a history of stroke are advised to stop taking vorapaxar. Patient who experienced a previous heart attack or peripheral arterial disease will continue.

"Despite all of the progress that has been made, cardiovascular disease remains the world's leading killer. Merck thanks the researchers and the thousands of study participants around the world for their contribution to advancing the scientific community's understanding of this critical area of cardiovascular medicine," said Dr. Kim

Merck plans to complete the TRA-2P study before making any decisions about regulatory strategy for vorapaxar.

Image credit: morguefile