The German drugmaker hired an outside investigator, who concludes two Bayer scientists didn’t try to mislead the FDA when they withheld data raising safety questions about the Trasylol blood-clotting drug.

Backdrop: Last fall, an FDA panel declared that Bayer’s Trasylol, a drug used to reduce bleeding during bypass procedures, was safe and effective, and voted unanimously to keep the med on the market. That was on Sept. 14. But a few days later, the FDA was contacted by Alexander Walker of Harvard’s School of Public Health, who said Bayer hid evidence. He was hired by Bayer six months earlier to review a 67,000-patient database and compare Trasylol side effects with two other anti-bleeding drugs.

The disclosure caused a furor, especially after it became known that Bayer employees failed to notify the FDA of the study, which showed that Trasylol can increase risk of death, kidney damage, heart failure and stroke. To clear its name, Bayer hired an outside lawyer to investigate.

And so Bayer’s investigator reports (read the report here) that company scientists Ernst Weidmann and Kuno Spenger, who works in Bayer’s German drug safety group, did indeed know of the study on Sept. 14….

…but the drugmaker didn’t make the study public until after the Sept. 21 meeting held by FDA. Why? According to the report by lawyer William Taylor of Zuckerman Spaeder, the employees didn’t disclose the results because they had questions about how the study was conducted, the AP reports.

“This failure was not motivated by any intent to conceal the existence of the study but was regrettable human error,” Bayer said in a statement on the drugmaker’s Trasylol web site. While understandable, Bayer said it viewed the decision as “a serious error in judgment.”

Bayer spokeswoman Staci Gouveia tells the Associated Press that the pair is still with the company but have been removed from their previous positions. Since the incident, Bayer said it has added additional checks and balances to its system for reviewing drug studies so that company officials are kept abreast of safety issues.

The FDA added additional safety warnings to Trasylol labeling in late 2006. Annual sales of the drug fell 33 percent to $195 million in 2006 compared with the prior year.