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Canadians at risk of blood clotting and strokes have a more convenient blood thinner option that doesn't require them to have their blood monitored regularly the way some people taking an older blood thinner do. ((Juan Carlos Ulate/Reuters))

A new blood thinner is easier to use to prevent clotting and strokes, but researchers in B.C. caution it may pose serious risks for some patients.

Tens of thousands of patients in Canada have taken warfarin, also used as a rat poison, to reduce their risk of clotting and stroke. But people taking warfarin may need to have their blood tested regularly to check how well it is working.

Earlier this month, a study of 18,000 people, published in the journal Lancet Neurology, suggested a new drug, dabigatran, will prevent more strokes and save lives. The drug was recently approved by Health Canada based on those findings.

"This new drug is much more effective than the current therapy, and safer, and on top of that it's much easier to use," said study co-author Dr. Stuart Connolly, director of cardiology at McMaster University in Hamilton.

Patients on dabigatran don't need to have their blood monitored, so more people will be able to take it, he said.

But pharmacist Aaron Tejani of the Therapeutics Initiative at the University of British Columbia, a group that independently evaluates clinical drug-trial data for doctors and pharmacists, is worried about a "signal of harm" in the data from the trial comparing dabigatran with warfarin.

"More people receiving dabigatran were experiencing myocardial infarctions or heart attacks," Tejani said.

Those in the dabigatran group also had more cases of major stomach bleeding compared to those taking warfarin. It's not clear if the problems were caused by the new drug.

The only way to find out would be to look at the full data of serious adverse events, such as heart attacks, strokes and problems requiring hospitalization, from the clinical trial, Tejani said.

So far, the dabigatran researchers have refused to share that information with Tejani and his colleagues to evaluate independently before the new approach is widely adopted.

Patient safety paramount

Subsequent papers have dismissed the heart attack concerns, Connolly said in an email. The trial database won't be released because researchers involved in the study want to publish their own papers on the findings, he added.

Since dabigatran was first approved a couple of years ago to prevent clots after hip and knee surgeries, Health Canada's database of adverse reactions has shown about 12 dozen reactions that health-care professionals suspect were related to the drug, including two deaths.

Tejani believes that when it comes to drugs, patient safety should trump proprietary concerns, a view supported by a recent report from the Health Council of Canada. The report's authors recommended that data from drug studies should be available and transparent.

The more information that is available to independent researchers, the better the chance of catching potential problems, agreed  Ingrid Sketris, a pharmacy professor at Dalhousie University in Halifax.

"It's important not only just to have the adverse drug reaction, but also more information about trying to understand why the adverse drug reaction occurred," Sketris said.

Tejani recalls the lessons of Vioxx, a blockbuster pain drug that was taken off the market in 2004. Data from early Vioxx studies showed it increased the risk of heart attacks, but by the time the data came to light, tens of thousands of people had died.

The original study was funded by Boehringer Ingelheim, which developed dabigatran.