Atrial fibrillation is an irregular heart rhythm affecting about 3 million Americans. The most serious risk of atrial fibrillation is stroke, caused by a blood clot forming in the abnormally beating heart chambers and traveling to a blood vessel in the brain. For over 50 years the mainstay of atrial fibrillation treatment has been the anticoagulant warfarin (better known by the brand name Coumadin) which effectively decreases the risk of stroke by preventing blood clots.
By the way, medicines that prevent blood clots are frequently called “blood thinners”, but they don’t thin the blood or affect blood viscosity. They prevent clotting. “Anticoagulant” is a more accurate term. Use the word at your next party (ideally while holding a bloody Mary) and your friends will marvel at your verbal precision.
Where was I? Oh, yeah.
Warfarin is probably the least convenient and most dangerous medication in common use. The reason is that the amount of anticoagulation caused by a given dose of warfarin varies wildly from one patient to the next and also varies in the same patient over time. Other medicines and certain foods can increase or decrease the anticoagulation caused by warfarin. Frequent blood tests are therefore required to adjust the dose. Too much warfarin increases the risk of life-threatening bleeding. Too little warfarin raises the risk of stroke from atrial fibrillation.
A group of new medications are now promising to eliminate the dangers and hassles of warfarin. I wrote two years ago about dabigatran (Pradaxa), an anticoagulant which is now on the market and is at least as safe and as effective as warfarin. Since then, another anticoagulant, rivaroxaban, has also been shown in a large trial to be superior to warfarin in safety and efficacy.
This week a third anticoagulant, apixaban, joins the group proven to be superior to warfarin. A study published in the New England Journal of Medicine (NEJM) randomized over 18,000 patients with atrial fibrillation to warfarin or apixaban. The patients were followed for almost two years. The patients on apixaban had fewer strokes, fewer episodes of major bleeding, and less mortality. An accompanying editorial in NEJM proclaims “a new era for anticoagulation in atrial fibrillation”.
Besides the fewer episodes of bleeding and stroke, a major advantage of these new medications is that they are prescribed at a fixed dose and do not require blood test monitoring.
Like many new medications, these new anticoagulants are relatively expensive (though less expensive than having a stroke or a life-threatening bleed). And like many old medications, warfarin is dirt cheap. So the transition away from warfarin may take some time. Nevertheless, its days in use for atrial fibrillation are numbered. Afterwards, it will likely still be useful in another role it has played for many years – as rat poison.
Study Gives Lift to Drug That Cuts Stroke Risk (Wall Street Journal article, see especially the handy chart summarizing the new anticoagulants)
A New Blood Thinner May Outperform Coumadin (My post two years ago about Pradaxa, dabigatran, the first oral alternative to warfarin.)
A New Era for Anticoagulation in Atrial Fibrillation (New England Journal of Medicine editorial, free without subscription)
Apixaban versus Warfarin in Patients with Atrial Fibrillation (New England Journal of Medicine article, free without subscription)
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