Under the US government pressure, Bayer AG said Monday 5 November 2007 it halted worldwide sales of its antibleeding drug Trasylol after a Canadian clinical study found it could be linked to a higher risk of death than other drugs.

The Food and Drug Administration (USA) asked the company to stop selling the drug, used to prevent excessive bleeding during heart bypass surgery, pending detailed review of preliminary results from the Canadian study. The study comparing the safety and efficacy of the drug with two others was recently halted.

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 Health Canada.

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.

The Canadian study comparing the safety and efficacy of Trasylol with two other drugs was recently halted. Preliminary results from the study suggested Trasylol increased the risk of death when compared with the other drugs. The trial was to include 3,000 patients.

"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. But he said that if individual doctors felt certain patients could benefit from the drug, the FDA would help Bayer explore options for keeping the drug on the market in a limited way.

The 5 November announcement came a month after FDA advisers recommended Trasylol remain on the market despite its links to an increased risk of death and other serious side effects.

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 latest advisory committee meeting in September 2007 did not find the safety concerns compelling enough to recommend a withdrawal, according to Dr. Gerald Dal Pan, director of the agency's Office of Surveillance and Epidemiology. Before making a decision the committee was interested in obtaining data from a randomized clinical trial like the halted Canadian study.

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 have 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."

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.

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

"Once the complete ... 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.