The Patient-Centered Outcomes Research Institute (PCORI) provided researchers in California and Massachusetts a total of $6.5 million in funding for two studies that will compare the effectiveness of anticoagulants in preventing blood clots in the veins and lungs.

For decades, physicians would prescribe warfarin to treat patients with pulmonary embolism, which PCORI said accounts for nearly 500,000 hospitalizations and 100,000 deaths per year in the U.S.

In recent years, the FDA has approved oral anticoagulants as an alternative to warfarin. The new anticoagulants are apixaban (Eliquis), dabigatran (Pradaxa), edoxaban (Savaysa) and rivaroxaban (Xarelto). PCORI said the drugs are often used for longer than three months and are effective, but they also may cause serious bleeding.

Researchers at the University of California, San Francisco will receive $3.5 million to evaluate patients who took one of the five drugs. They will compare the drugs and examine if the benefits and harms associated with the drugs differ for patients who are older, have impaired kidney function or are at a higher risk of bleeding.

Researchers at Brigham and Women’s Hospital in Boston will receive $2.9 million to compare the four oral anticoagulants with each other and with warfarin for extended use in patients who are being treated for the first time for clots.

“Blood clots in the veins and lungs can cause serious and sometimes deadly results such as organ damage, stroke, and heart attacks,” PCORI executive director Joe Selby, MD, MPH, said in a news release. “The research we are supporting gives the patients a vital role in finding the evidence on these newer medications that they, along with their providers, can use to make treatment decisions.”