MARLEY SEAMANNEW YORK (AP) ¿ Cubist Pharmaceuticals Inc. said Thursday it stopped enrolling patients in trials of a drug intended to reduce bleeding during heart surgery because of deaths among patients that took it. Cubist said a data monitoring board wants to assess the difference between patients on the drug, and those who were on an alternative treatment. Overall, the rate of deaths in the studies was consistent with expected outcomes, and the causes of death were typical for a group of patients that was at a high risk for bleeding during cardiac surgery, Cubist said. The monitors suggested Cubist suspend enrollment in a study that compared the experimental drug to Cyklokapron, a drug that is approved in Europe to control bleeding. Cubist decided to stop enrolling patients in that study, and in a second study that compared its drug to a placebo. The news battered shares of Dyax Corp., which discovered the compound and licensed it to Cubist. The drug is Dyax's lead product candidate, and in afternoon trading, shares of the Cambridge, Mass., company lost 29 cents, or 6.9 percent, to $3.94. The drug was called ecallantide, but Cubist is now designating it as CB-500,929. Cubist said it had enrolled more than 450 patients in the two studies, which were called CONSERV-1 and CONSERV-2. It planned for about 650 patients. The Lexington, Mass., company plans to continue collecting data on patients who were already treated and analyze the results. CB-500,929 is intended for use in "on-pump" surgeries, or operations in which a patient's heart is stopped, and blood is kept flowing with a cardiopulmonary bypass machine. Such operations include coronary artery bypass graft surgeries and heart valve replacements and repairs. Following an analyst upgrade, Cubist shares rose 76 cents, or 4.4 percent, to $18.05.