WASHINGTON - Bayer AG halted worldwide sales Monday of its anti-bleeding drug Trasylol at the request of U.S. and foreign health officials pending further analysis of a Canadian study that suggests it's linked to a 50 percent higher risk of death than the other drugs in the clinical trial.

The Food and Drug Administration asked the company to stop selling the drug, used to prevent excessive bleeding during heart bypass surgery, until it could receive and review further results from the study. The study comparing the safety and efficacy of the drug with two others was recently halted.

"FDA cannot identify a specific patient population where we believe the benefits of using Trasylol outweighs the risk," said Dr. John Jenkins, director of the agency's Office of New Drugs, during a briefing Monday.

Bayer, based in Leverkusen, Germany, said it made the decision to suspend sales after talks with FDA, the German Federal Institute for Drugs and Medicine Products along with the Canadian health department.

In the U.S., Trasylol is the third prescription drug to be suspended from sale this year.

The suspension may be only temporary, at least for some patients. The FDA said it was exploring with Bayer whether to make the drug available on a restricted basis for use by physicians in certain patients they believe could benefit from the drug.

"The broad use of the drug, unless there is a real surprise when the data are finally analyzed, is unlikely to ever return," predicted Dr. A. Michael Lincoff, vice chairman of research in the Cleveland Clinic's cardiovascular medicine department, who's advised the FDA on the drug.

Trasylol, also known as aprotinin, works by blocking enzymes that dissolve blood clots. It is designed to stem blood loss and enable patients receiving heart bypass surgery to avoid transfusions.

Bayer estimates Trasylol has been used in roughly 4.8 million people over the last 14 years. Last year, about 110,000 U.S. patients, and another 87,000 overseas, received the drug, though its use has declined in the wake of earlier indications of safety issues, said Dr. Timothy Gardner, a Delaware heart surgeon Gardner is a spokesman for the American Heart Association, whose annual scientific conference in Orlando, Fla., buzzed Monday with news of the drug's suspension.

While current year usage figures were not available, Bayer estimates worldwide sales of the injection drug were roughly $135 million for the nine months through September. The U.S. accounted for about $91 million of that total.

The Canadian study comparing the safety and efficacy of Trasylol with two other drugs was halted when preliminary results suggested Trasylol exposed patients to a greater risk of death. The actual number of deaths was not available.

The FDA said it requested the drug be pulled rather than wait the six weeks for further, more definitive results from the study, which was to include 3,000 patients.

Monday's announcement came after a September recommendation from FDA advisers that Trasylol remain on the market despite its links to an increased risk of death and other serious side effects. Results from the Canadian study were not available at the time, although Lincoff and the other panel members knew it was ongoing.

The FDA's Jenkins said it was not a mistake to keep the drug on the market when FDA first learned of potential safety concerns.

"As we've learned about the safety concerns from the observational studies, we've taken those data very seriously," he said. "We've gone to two FDA advisory committee meetings for public discussion of these data."

The FDA approved the drug in 1993. It began re-evaluating the drug's safety after the January 2006 publication of two studies that linked the drug's use to serious side effects, including kidney problems, heart attacks and strokes.

More recent studies further suggested the drug also raises the risk of death. One of those studies previously was withheld by Bayer from the FDA due to what a company investigation later characterized as a "regrettable human error."

"The well-deserved, adverse publicity has forced the company to do something," FDA critic Dr. Sidney Wolfe said of the worldwide suspension.

Dr. Rafel Rieves, director of FDA's Office of Medical Imaging and Hematology, noted during Monday's briefing that the Canadian study included patients undergoing multiple types of heart surgery, beyond the specific type of bypass for which use of Trasylol is approved. He said dissecting the study will be important in further evaluating the risks and benefits of the drug.

There are not many treatment options for patients at risk for excessive bleeding during cardiac surgery, the FDA noted. The agency said it was working with Bayer to phase Trasylol out of the marketplace in a way that does not cause shortages of other drugs used for this purpose.

"Unfortunately, there's nothing like it in the pipeline" to fill the gap, and the drug was particularly useful for certain patients, the Heart Association's Gardner said.

Bayer said it wanted to review the results from the Canadian trials before moving forward.

"Once the complete (study) dataset is available, Bayer will work with health authorities to evaluate whether these data have any impact on the positive benefit-risk assessment for Trasylol," the company said. "At that time the temporary marketing suspension will be reevaluated."

Shares of Bayer rose nearly 1.2 percent to euro57.30 (US$83.02) in Frankfurt.

___

Associated Press writers Matt Moore in Frankfurt, Germany, and Natasha T. Metzler in Washington contributed to this story.