Table of Contents
Anticoagulant (blood thinning) medications prolong millions of lives.
By stopping the formation of blood clots, anticoagulants prevent catastrophic consequences of atrial fibrillation, deep vein thrombosis, venous thromboembolism, pulmonary embolism, congestive heart failure, stroke, heart attack (myocardial infarction), and genetic or acquired hypercoagulation disorders. Anticoagulants prevent blood from clotting in the lines leading from transfusion bags and in kidney dialysis machines. And they prevent the formation of potentially dangerous clots before, during, and after surgery.
All Anticoagulants Carry the Risk of Serious Side Effects
The clotting of blood is a multi-step process, and different anticoagulants stop different parts of the process. The coumarins, a group of drugs that includes warfarin, also known as Coumadin, which is more commonly used in the US and UK, and acenocoumarol and phenprocoumon, which are more commonly used in the rest of the world, act by antagonizing the effects of vitamin K. The coumarins bind to and deactivate an enzyme called vitamin K epoxide reductase, making it less available to activate the clotting of blood.
Long-term use of coumarins requires monthly monitoring of their levels in the bloodstream. Overdoses can cause serious bleeding. It's easy to mess up--and doctors only prescribe them for long-term use for specialized situations, such as prevention of blood clots after heart valve surgery.
Heparin, a naturally occurring protein usually extracted from pig intestines, and low molecular weight heparin (Lovenoxi), a more highly refined version of heparin, stop blood clots by activating a protein called antithrombin III, which prevents clotting of the blood. These medications are given by injection, but they do not have to be as closely monitored as some other anticoagulants, but severe bleeding is a real possibility.
Oral Anticoagulants Easier to Use, Improving Safety
More recently, the pharmaceutical industry has developed a large number of oral anticoagulant medications, taken by mouth, not requiring an injection, that don't require frequent monitoring by doctors.
Another drug in this class is not on the market because it was found not actually to achieve its intended effect, reducing the risk of heart attack, but increased the risk of serious bleeding by 300%.
The very popular anticoagulant Brilinta (ticagrelor), sold outside the United States as Brilique or Possia, stops blood clots by acting as platelet activation factor (PAF) inhibitor, preventing blood platelets from clumping together to form a clot. Popular for preventing second heart attacks, this medication can cause severe bleeding in the liver and colon. Diabetics who have received coronary artery stents should not take Brilinta (although they still are likely to need a different coagulant drug).
And an even more popular anticoagulant drug that acts through the same mechanism, Plavix (clopidogrel), reduces the risk of heart attack after the placement of a stent in a coronary artery but can cause gastrointestinal bleeding in up to 2% of people who use it every year.
An Understandable Warning
Because all anticoagulants can cause unintended bleeding, all users must exercise caution not to suffer cuts, scrapes, or internal injuries. But because the easy to use oral anticoagulants can cause serious internal bleeding in the liver, many doctors have assumed that people who have liver disease simply cannot use them. Recent studies suggest this precaution may not be necessary.