In daily life, you can often see elderly people around taking aspirin, most of them are patients with cardiovascular diseases, and they take small doses of aspirin according to their doctors’ requirements, with the aim of preventing platelets from clumping into blood clots and blocking blood vessels. At the same time there is another class of drugs, namely warfarin, which we do not encounter as much as aspirin in daily life, but among patients with atrial fibrillation, there are many who need to take this drug for a long time, also with the purpose of preventing blood clots from forming.
The same is to prevent blood clots, why some people take aspirin, while others need to take warfarin? For some people, they even need to take both aspirin and warfarin together? Can these two medications be substituted for each other?
Two systems related to blood clotting
”In fact, the mechanism of action of warfarin and aspirin are completely different, and they cannot be considered the same class of drugs.” Professor Zhu Jun, a consultant expert at the Emergency and Critical Care Center of Fu Wai Cardiovascular Hospital, Chinese Academy of Medical Sciences, said that strictly speaking, blood coagulation involves many mechanisms in the body, and there are two main systems.
One major system is the coagulation factors present in the blood plasma, of which more than a dozen have been discovered. When one of these coagulation factors is activated at the source, a series of chemical reactions, commonly referred to as a “coagulation waterfall,” occurs. As a result, fibrinogen in its soluble state becomes insoluble fibrin, and a clot is created. From the perspective of thrombosis-related diseases, such clots caused by clotting abnormalities are found in the venous system and the atria of the heart.
Another system is related to platelets. In the normal state, platelets keep circulating in the blood and do not aggregate. However, when a blood vessel is damaged due to certain factors, such as a cut on the finger, which exposes the body’s tissues to the blood, platelets are activated, so platelets begin to aggregate, and with the involvement of other factors such as red blood cells, a clot is formed. Blood clots caused by platelet aggregation occur mostly in the arterial system.
Zhu Jun said, “Since these are two completely different systems, we call drugs that act on the former ‘anticoagulants’ and drugs that act on the latter system ‘antiplatelet agents,’ and their mechanisms of action are completely different.”
Two types of drugs for different diseases
Zhu Jun pointed out, like everyone commonly used aspirin, is through the inhibition of platelet aggregation and play a role, it does not have the role of anti-coagulation, so belong to the “anti-platelet drugs”; while warfarin is the role of a series of chemical reactions involved in the clotting factors, to fight the clotting of blood, so belong to the “Anticoagulant”.
In addition to aspirin, there are many other kinds of antiplatelet agents, such as clopidogrel. Although they act on different platelet receptors, they all have one goal, which is to inhibit platelet aggregation. The most commonly used oral anticoagulant with a clear safety profile is warfarin, and some new anticoagulants have recently been introduced.
Due to completely different mechanisms of action, anticoagulants and antiplatelet agents are used separately in clinical practice to treat different diseases. In some diseases clots are formed due to a slowing down of blood flow, most typically in atrial fibrillation and venous thrombosis. The medication needed in this case is warfarin to counteract the clotting of the blood.
In some diseases, platelet aggregation is the main cause of thrombosis, most typically in coronary heart disease. Once the plaque ruptures, platelets receive stimulation from human tissue and mistakenly think that the blood vessel has “ruptured” and start to aggregate to form a blood clot, which may eventually block the blood vessel. This is the principle of some acute myocardial infarction. This is where aspirin, or even aspirin plus clopidogrel, are used together to counteract platelet aggregation.
Because the two drugs have different mechanisms of action and different indications, in some patients, both aspirin and warfarin may be used, such as patients with coronary artery disease with atrial fibrillation. “This is not only the case, but it is also more common in patients in cardiology.” Zhu Jun explained.
Anti-platelet therapy has three major misconceptions
Zhu Jun stressed that at present, in the prevention of thromboembolism in atrial fibrillation, the clinical and public mind is more receptive to aspirin class of antiplatelet drugs, and less receptive to warfarin anticoagulation therapy. In fact, there are three major misconceptions about the use of antiplatelet agents for the prevention of thromboembolism in atrial fibrillation.
Myth 1: The efficacy of antiplatelet therapy is overestimated.
Antiplatelet agents used for stroke prevention in atrial fibrillation are not completely ineffective, but aspirin is only 1/3 as effective as warfarin in reducing thromboembolism. studies have also found that in elderly patients (>75 years), the effectiveness of aspirin in preventing thromboembolism does not increase with age, whereas warfarin does, and the incidence of bleeding events is similar in both.
Myth 2: The bleeding complications of antiplatelet agents are underestimated.
In clinical practice, aspirin has also caused a high number of bleeding events. The U.S. Food and Drug Administration (FDA) has suggested that patients with high-risk atrial fibrillation are also at increased risk of bleeding with aspirin and are not safer than warfarin; instead, the incidence of bleeding can be reduced very low with warfarin under close monitoring.
Myth 3: Antiplatelet therapy is superior to anticoagulation therapy.
This perception reverses the position of aspirin and anticoagulants, and even combined antiplatelet therapy (aspirin plus clopidogrel) is much less effective than warfarin. Therefore, antiplatelet therapy is only considered clinically when no anticoagulant can be used.