Merck Clot Preventer Linked to Bleeding Risk

Merck & Co's experimental blood clot preventer vorapaxar can cause bleeding in patients who previously suffered a stroke, investigators involved in clinical trials of the drug confirmed on Wednesday.

Merck said last week that an independent committee set up to monitor clinical trials of the drug determined that vorapaxar was inappropriate for patients with a history of strokes, but no details were given about the risks they faced.

The drug, meant to prevent heart attacks and strokes or their recurrence, was considered a crown jewel in Merck's pipeline, and the news erased nearly $8 billion from the company's market value.

Merck said on Wednesday that it informed investigators of the Data and Safety Monitoring Board's recommendations.

"They have observed an increase in intracranial hemorrhage in patients with a history of stroke that is not outweighed by their considerations of potential benefit," Dr. Eugene Braunwald, chairman of the vorapaxar trial, said in a statement.

He said the committee also recommended that patients without a history of stroke, including those who had a previous heart attack or peripheral arterial disease, continue in the trial.

Merck said previously that a second trial of vorapaxar as a treatment for patients with acute coronary syndrome had been discontinued.