FYI: http://news.yahoo.com/s/ap/20110113/...rck_drug_trial

Shares of Merck & Co. plunged Thursday after the drugmaker unexpectedly halted one late-stage trial of a potential blood thinner and said it will immediately stop giving the drug in another study to patients who have had a stroke.

The Whitehouse Station, N.J., company is studying vorapaxar for the prevention of cardiac events and had planned to submit the drug this year to the Food and Drug Administration for approval. But Merck Research Laboratories President Peter Kim said in a conference call with analysts the company will have a new time frame after it analyzes information from the two studies.

Merck said it was stopping a study of the drug in patients with acute coronary syndrome because that trial had reached a pre-determined number of endpoints, or medical issues like cardiovascular deaths, heart attacks or strokes. That gave researchers enough data to analyze the drug's safety and effectiveness.

Dr. Robert Harrington said in a statement that was an "unexpected development." Harrington is the study chairman and director of the Duke Clinical Research Institute.

Researchers also planned to immediately stop giving the drug to stroke patients in a separate study examining people who had had a previous heart attack, stroke or peripheral artery disease. They will continue studying the rest of the patient population, which is about 75 percent of people enrolled in the study. That trial's chairman, Dr. Eugene Braunwald, said in a statement the potential treatment "does not appear to be appropriate in patients who have had a stroke."

Merck officials declined to elaborate in the conference call on whether there were bleeding concerns with the drug or why the trials were stopped and altered. The drug company made the decision based on recommendations from an independent Data and Safety Monitoring Board that reviewed the trials.

Merck acquired vorapaxar when it bought Schering-Plough Corp. in 2009.