Boehringer Ingelheim GmbH didn’t tell regulators that adjusting the dose of blood thinner Pradaxa could make it safer, according to a BMJ probe into the drug that’s been linked to patient deaths.

The German company’s own analysis indicated that adjustment of the dosage might help reduce the risk of major bleeding, a feared side effect of blood thinners, Deborah Cohen, BMJ’s investigations editor, wrote today. Internal documents from 2011 showed that some Boehringer employees were concerned that if they advised the monitoring of Pradaxa levels it could damage the marketing case for the drug, the BMJ wrote.

“Our company has provided regulators with the complete data set and analyses of clinical evidence demonstrating the efficacy and safety profile of Pradaxa,” Boehringer said in a statement, adding that BMJ made “misleading statements.”

Boehringer agreed in May to pay $650 million to settle the majority of U.S. lawsuits filed over Pradaxa, which has been linked to more than 500 patient deaths. Boehringer had presented its pill as a convenient alternative to the older blood thinner warfarin, which requires regular blood-testing to ensure the correct dose. The European Medicines Agency approved the product in 2011, a year after the U.S. Food and Drug Administration.

“Patients and doctors tolerant of unknown risk and close monitoring will have to choose which drives them more strongly, with the conservative option being warfarin,” Rita Redberg, a professor of medicine at the University of California, and medical resident Blake Charlton wrote in an editorial accompanying the report. The BMJ “illuminates a lack of transparency about the safety” of the drug, they wrote.

Boehringer’s Pradaxa won FDA approval in October 2010 and had 1.2 billion euros ($1.62 billion) in sales last year.

The drugmaker, based in Ingelheim, Germany, said it explored in 2012 whether monitoring plasma levels would improve the efficacy and safety of Pradaxa via mathematical models. The results didn’t support monitoring, and were therefore not provided to regulators. The company said it found that other factors, such as age, kidney function and certain medications, are critical factors that can contribute to bleeding risk.

“BMJ did not put this information into proper context,” the company said, adding the FDA and EMA have said Pradaxa “provides an important health benefit when used as directed.”