Newer anti-clotting drugs such as Bristol-Myers Squibb Co.'s Eliquis cause less risk of a major bleeding episode than warfarin — the oral anticoagulant developed 70 years ago, according to a new study published in the British Medical Journal.

Researchers at the University of Nottingham compared warfarin with the three most common oral anticoagulants — dabigatran, also known as Pradaxa and made by Boehringer Ingelheim GmbH; Bayer AG's Xarelto, or rivaroxaban; and Eliquis, or apixaban — in patients with and without atrial fibrillation. Atrial fibrillation, or AF, is an irregular heartbeat that increases the risk of stroke and heart disease.

Warfarin, also known as coumadin, was first developed as a rat poison in 1948. It was approved for use in humans in 1954 after scientists realized that it interfered with the production of vitamin k, which helps blood to clot. Warfarin has been the main treatment for potentially fatal blood clots known as venous thromboembolism or VTE, but patients need to have regular blood tests to check that they have the right dose of the drug in their bloodstream.

Although clinical trials have shown a reduced or similar risk of major bleeding for the newer anticoagulants compared with warfarin, as the trials involve carefully selected patients, bleeding rates do not reflect those seen in everyday, according to the study.

In an observational trial of 196,061 patients who were prescribed anticoagulants between 2011 and 2016, the U.K. researchers found that the risk of major bleeding was lower in those taking Eliquis. The patients were monitored for major bleeds leading to hospital admission or death, ischemic stroke and VTE.

Taking account of several known risk factors, the researchers found that apixaban was associated with a lower risk of major bleeding, particularly brain and gastric bleeds, in patients with and without AF, compared with warfarin.

"Our results give an initial, reassuring, indication of the risk patterns for all patients taking anticoagulants, in particular with respect to those prescribed apixaban," concluded the researchers, led by Yana Vinogradova, of the University of Nottingham.