About 30,000 Australians on a new blood-thinning drug could have been put at increased risk of internal bleeding because the drug's makers withheld safety information.

Figures obtained by the ABC reveal Pradaxa has been associated with 280 deaths in Australia and 1,400 adverse drug reactions in the past five years, including abdominal bleeding, brain haemorrhages, strokes and heart attacks.

By comparison, the older blood-thinning drug Warfarin has been linked to 30 deaths and 270 reactions over the same period.

Medical experts say the side effects and death figures are disparate because Pradaxa is a new medication and there has been more reporting of adverse events from it compared to Warfarin.

A British Medical Journal investigation released last week found the makers of Pradaxa withheld some of their internal analysis of the new "blockbuster" drug because they were worried it would affect sales.

The analysis suggested the medication could be made safer if patients using Pradaxa had their blood levels monitored, which is the same as Warfarin.

The information was unearthed during court proceedings in the United States.

Pradaxa's maker, Boehringer Ingelheim, has announced it will pay out $650 million to settle 4,000 lawsuits across the United States.

British Medical Journal investigations editor Deborah Cohen, who authored the journal's article, said it fell to regulators to answer questions about the drug's approval conditions.

WARNING: Specialists say it is important patients do not stop taking Pradaxa, because stopping suddenly could increase the risk of stroke. People with concerns should speak with their doctor.

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"The company had this information and we found they never released it to the drug regulators even when they started asking questions," Dr Cohen said.

"Really, the onus is on the drug regulators to look into this issue."

In Australia, the regulator is the Therapeutic Goods Administration (TGA). The TGA said while it was aware of the article, there was no new information that would change the risks and benefits of the medication.

Boehringer Ingelheim said the analysis in question was based on a hypothesis they later found did not stack up, so the information was never released.

In a statement, the company said age and kidney function were the biggest factors in terms of bleeding prevention, not monitoring.

'Company put marketing ahead of safety'

When it was launched in 2009 Pradaxa was the first drug in 50 years to rival the commonly prescribed Warfarin.

A big selling point was that patients did not need to have their blood levels monitored.

This was particularly helpful for patients who reacted to Warfarin, struggled with required dietary restrictions, or lived in remote areas and could not access regular testing.

Boehringer Ingelheim has been criticised for its heavy-handed approach to marketing Pradaxa.

Dr Cohen's investigation suggested the company sat on its analysis regarding the need to monitor blood levels because it would affect its marketing strategy.

"The data suggests [Pradaxa is] about as effective and safe as Warfarin, in some ways it might even be slightly better," Dr Cohen said.

"The key allegation here is the company had an opportunity to make [Pradaxa] far safer and it declined that opportunity because of marketing.

"To be blunt, the company had put marketing ahead of safety."

Evan Ackerman from the Royal Australian College of General Practitioners said the case showed pharmaceutical companies could not be relied upon to self-regulate.

"I think the regulators need to have some action here," he said.

"It is now quite clear that patient safety issues are involved ... there are some significant variations in bleeding tendencies when people are prescribed standard doses of the drug."

Dr Ackerman said Boehringer Ingelheim was involved with inappropriate marketing activities when the drug was launched.

"They gave this quite significantly dangerous drug to general practitioners without the education, or with limited education, without conveying the true risks associated with this drug," he said.

"I think it's clear we need open disclosure now of all these drug trials that the drug companies run."

Pradaxa has no antidote

A key difference between Pradaxa and Warfarin is that Pradaxa has no antidote.

If patients on Warfarin suffer internal bleeding, emergency doctors can reverse it with Vitamin K.

If patients on Pradaxa sustain any kind of trauma from an accident or fall, which is common in the elderly, doctors find it difficult to stop the bleeding.

There are therapies they can use such as fresh frozen plasma, but it is more difficult.

Proponents said a reversing agent was in development but it was not yet available.

"I know it's been concerning emergency doctors for some time that they're having to deal with patients who were having major bleeds and they've been unsure about what to do," Dr Cohen said.

"The surgeons were phoning up the company asking what to do ... there was nothing the surgeons could do to stem the bleeding."

New generation of medicines

Pradaxa is one of a number of a new generation of anti-coagulants. They all pose a risk of internal bleeding, including Warfarin.

Pradaxa is mainly approved for people with irregular heart rhythms, known as atrial fibrillation (AF), which puts them at increased risk of stroke.

There are about 240,000 Australians with AF and the condition becomes more common as people get older.

About 24,000 were put on Pradaxa for free when it was first launched in Australia as part of a trial.

Pradaxa is also approved for people who have had major leg surgery, such as hip and knee replacements, to prevent clots.

By contrast, about 2.5 million scripts for Warfarin are written each year.

Data not witheld, Boehringer Ingelheim says

The makers of Pradaxa said they never withheld data from regulators.

They said the suggestion that safety could be improved with regular blood level monitoring was a hypothesis they tested in 2012 using mathematical models.

They said this piece of analysis regarding testing did not stack up when they applied it to data from its major clinical trial and so it was never released.

The company said European and US regulators ran their own similar models and came up with similar results.

In a statement, Boehringer Ingelheim said all the safety evidence, when combined, did not support blood monitoring.

"The research shows that individual patient characteristics, such as age, kidney function and certain medications, are critical factors in contributing to the risk of bleeding," it said.

Chief medical officer Klaus Dugi said the company made a "robust effort" to find ways to use blood monitoring to improve safety of the drug.

"The truth is, if these approaches could have been developed, we would have used them to the benefit of patients," he said.

The data was intended to be part of a journal article, which was later published.

In its investigation, the British Medical Journal found internal emails, released during US court proceedings, and a draft version of the journal article.

The draft article suggested there was an "optimal plasma concentration" range which could be achieved using blood monitoring.

In internal emails, a medical team leader said he was "not happy with the conclusion" about an optimal range.

Another company official said: "The publication [of the article] will [do] more harm than be useful for us, neither in the market but especially harmful in the discussions with regulatory bodies."

Dr Cohen said the company's analysis was based on data the company used to have the drug approved.

"You can't have it both ways. It doesn't stack up when it's convenient for you and not stack up when it's inconvenient for you," she said.

Therapeutic Goods Administration responds

The TGA has done two safety reviews into Pradaxa since it was first approved.

A spokeswoman for the TGA said it was aware of the journal article.

"The TGA has considered the articles and notes there is no new information that would indicate a change in the benefits and risks of Pradaxa," she said.

She said the current advice given to doctors, known as Product Information, provided extensive information on the safe use and monitoring of patients to prevent risk of bleeding.

"This includes careful monitoring of renal [kidney] function and use in the elderly," she said.

"The Product Information also includes information on when to undertake coagulation testing and the tests that can be used."

She said the TGA would continue to monitor the safety of Pradaxa.

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