Patient's question triggers important study about blood thinners

Posted on Tuesday, September 16, 2014

Physicians around the world now have guidelines to help them determine the best oral blood thinners to prescribe to patients suffering from venous blood clots, thanks to an Ottawa Hospital patient who asked a question his doctor couldn't answer. These guidelines are included in a study published today in the Journal of the American Medical Association(JAMA).

"Right there in the clinic, he identified an important knowledge gap for clinicians. We decided to act on it and find the answer," says hematologist Dr. Marc Carrier, who is an associate professor at the University of Ottawa and a scientist at the Ottawa Hospital.

Dr. Carrier was treating Jamie Dossett-Mercer for significant blood clots in a leg vein that reached from his ankle to his groin, known as a deep vein thrombosis. If one of these clots were to break off, it could travel to his lung and cause a pulmonary embolism, which is often fatal. These two common medical conditions, whose combination is known as venous thromboembolism, are among the leading causes of cardiovascular death.

In recent years, a number of new oral anticoagulants have been approved to treat this condition. Faced with eight possible treatment options, Dossett-Mercer asked, "How do all these different blood thinners compare to one another?"

Dr. Carrier went looking for the answer. Although he found dozens of trials that studied the effects of different treatments separately, none had analyzed all the possibilities against one another.

His team reviewed 45 randomized trials (involving nearly 45,000 patients) using a process called network meta-analysis, which allowed them to set a baseline treatment against which to compare all others. All the clinical trials they found had compared the newer treatments to the standard of care (which is low-molecular-weight heparin (LMWH) with vitamin K antagonists).

Using the LMWH-vitamin K antagonist combination as the central node of the network, they compared the safety and effectiveness of seven other anticoagulant therapies for venous thromboembolism: unfractionated heparin (UFH) with vitamin K antagonists; fondaparinux with vitamin K antagonists; LMWH with dabigatran; LMWH with edoxaban; rivaroxaban; apixaban; and LMWH alone.

While they found no major differences in effectiveness and safety, there were some notable variations:

  • A higher percentage of patients taking the UFH-vitamin K antagonist combination experienced a recurrent blood clot within three months
  • A lower percentage of patients taking rivaroxaban and apixaban experienced a major bleeding event within three month

"This will help physicians tailor their care according to patient characteristics," says Dr. Carrier. "For example, if I am worried about recurrent clotting, but I'm not too worried about the risk of bleeding, then I can select the drug with the best safety profile."

"I was already impressed with Dr. Carrier's exceptional care," says Dossett-Mercer. "But that he would do this research based on a patient question is just astounding."

The complete article, entitled “Clinical outcomes associated with treatment of acute venous thromboembolism: A systematic review and meta-analysis”, was published on September 16, 2014, in the JAMA. The authors did not receive any external funding for this study.

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