Bayer AG stopped selling the drug last fall, after a Canadian study was halted because of deaths among patients taking Trasylol.
But the new research reignited controversy over Trasylol, which was on the market for 14 years and used by doctors to treat hundreds of thousands of heart bypass patients each year.
Bayer funded one of the two new studies, and had the preliminary results before a September 2006 federal hearing on the drug's safety - but did not present them.
The company issued a statement this week saying both the new studies are flawed. But the spokesman for a consumer advocacy group said the studies are convincing confirmation of the drug's dangers.
"I just don't know how much further evidence you need," said Dr. Sidney Wolfe of Public Citizen's Health Research Group. The new studies are being published this week in the New England Journal of Medicine.
Trasylol, known generically as aprotinin, was used in heart bypass surgeries to control bleeding. The U.S. Food and Drug Administration approved it in 1993 after studies showed its clotting powers clearly reduced the need for blood transfusions, and it became a top choice for surgeons.
The first new study looked at more than 10,000 patients who had bypass surgeries at Duke University Medical Center from 1996 through 2005.
It found that 6.4 percent of patients who were given Trasylol died within 30 days of the surgery, a rate nearly 2½ times higher than patients who got another drug or who received no treatment for excessive bleeding. At one year after surgery, almost 16 percent of Trasylol patients had died - again, roughly 2½ times higher than the other two patient roups.
But it's not clear why the people who took Trasylol died at a higher rate, said Dr. Andrew Shaw of Duke, the study's lead author.
The second study - the one funded by Bayer - looked at more than 78,000 patients nationwide in a period from Jan. 1, 2003 to March 31, 2006.
After adjusting for other factors, the researchers found the risk of death after surgery was 64 percent higher in the Trasylol group than in those taking a comparison drug.
The results did not change substantially from when they were first presented to company officials at Bayer in early September 2006, said Dr. Sebastian Schneeweiss of Harvard Medical School, the study's lead author. Bayer had the results before an FDA advisory committee meeting on the drug.
At that meeting, the FDA panel discussed a different study based on hospital records of thousands of patients, which found that those given Trasylol had higher rates of death and kidney failure that required dialysis. The study suggested as many as 2,000 patients a year died as a result of taking the drug.
At the time, some scientists had said the research was flawed and the deaths may have been caused by other factors. The committee voted to keep the drug on the market. Bayer officials said they did not discuss the Schneeweiss study with the committee because it was preliminary and they had questions about how it was done.
The more rigorous Canadian study compared Trasylol with two other drugs, and was halted last year when preliminary results suggested a higher risk of death with the Bayer drug.
The FDA requested the drug be pulled rather than wait for more definitive results from the Canadian study. Those results still have not been released.
Federal health officials should pursue criminal charges against Bayer for withholding information from its own study from the FDA panel in 2006, Wolfe said.
Bayer officials still say they believe Trasylol's benefits outweigh its risks when used properly. The company said it's waiting for the final results of the Canadian study before deciding whether to permanently suspend the drug's sales.
