More than 5 million people who have Medicare Part D in the United States are on anticoagulant medications. These life-saving blood thinners are used to treat and prevent blood clots and are also used to prevent strokes in people with atrial fibrillation and abnormal heart valves. Anticoagulants are essential in modern medicine, offering life-saving benefits when used correctly, but, like all medications, they come with crucial risks and responsibilities.
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What Are Anticoagulants?
So what exactly are anticoagulants, and how have they become so crucial to modern medicine?
Definition and Overview
Blood clotting is vitally important to prevent you from losing significant amounts of blood from even minor injuries. The process of clot formation has four stages: platelet plug formation, clot propagation, stopping clot formation, and removing the clot through a process called fibrinolysis.
Anticoagulants are medications that block one or more parts of the coagulation pathway. There are several types of anticoagulants available such as:
- Heparin and heparin derivatives
- Vitamin K antagonists
- Direct thrombin inhibitors (DTIs)
- Factor Xa inhibitors
Each of these classes of anticoagulants affects the coagulation pathway differently. Medications such as heparin and warfarin (a vitamin K antagonist) have been around for many years while DTI and Factor Xa inhibitors are relatively new on the scene.
History of Anticoagulants
The first anticoagulant medication to be discovered and used was found by a medical student in 1916. Unfractionated heparin was approved for clinical use in the 1930s after undergoing studies and purification. It wasn’t until the 1970s that researchers discovered how this medication actually worked.
Warfarin was discovered after the death of large numbers of cattle on cattle farms in the 1930s. Ultimately, the deaths were linked to spoiled hay, and dicumarol, a vitamin K antagonist, was discovered. Vitamin K antagonists were the first medications that were able to be administered orally.
Novel oral anticoagulants, the DTIs and Factor Xa inhibitors, have accelerated the advancement of anticoagulants by allowing for the targeting of specific clotting factors in the coagulation pathway. These compounds are designed to have fewer side effects and interactions with other medications.
Types of Anticoagulants
For many years, there were very few anticoagulant options, but recent advancements have allowed for new classes. There are now several types of anticoagulants to choose from.
Traditional Anticoagulants
Heparin is administered intravenously or as an injection under the skin. It binds to several proteins in the blood, but binding to the antithrombin III protein is how the medication exerts its anticoagulation effects.
Warfarin works by inhibiting the vitamin K epoxide reductase complex subunit1, which is an enzyme the body uses to activate vitamin K. Vitamin K is an important component required for the creation of several of the factors required for clot formation. Blocking the activation of vitamin K decreases the creation of these factors in the liver.
Direct Oral Anticoagulants (DOACs)
DTIs and Factor Xa inhibitors fall into a category of direct oral anticoagulants (DOACs).
DTIs bind directly to thrombin without requiring antithrombin as a mediator. This means that DTIs can affect both the thrombin that is soluble in the blood stream and that which is bound to fibrin. This means that it is more predictable than some of the other options because it doesn’t bind to other proteins in the blood. It also has fewer side-effects than heparin.
Factor Xa inhibitors reversibly bind the active site of factor Xa preventing them from interacting with other factors and blocking the final step in the creation of thrombin. This also them to work on the coagulation pathway from both sides and makes it a more efficient anticoagulant. Factor Xa doesn’t have many functions outside it’s role in the coagulation pathway, so blocking it has fewer side effects.
Medical Uses of Anticoagulants
There are many reasons why someone may need to have thinner blood, and different anticoagulants may be used for different purposes.
Preventing Blood Clots
Anticoagulant medications are used to both prevent and treat blood clots. Two common types of blood clots that are treated with anticoagulants include deep venous thrombosis (DVT) and pulmonary embolism (PE). DVT is a blood clot in the deep veins of the body, most commonly in the legs. PE is a blood clot (or other material)in the arteries of the lungs. The most common cause of a PE is a DVT.
Anticoagulants may be used to prevent blood clots in people who have an increased risk of developing a DVT or PE such as those who have a significant injury, are immobilized, have had a previous blood clot, or those who have a genetic condition that increases their risk such as factor V Leiden or a prothrombin mutation.
Cardiac Applications
Many people who have an irregular heartbeat called atrial fibrillation (a. fib) or problems with their heart valves can benefit from being on an anticoagulant to prevent complications such as stroke. Healthcare providers use a calculator called a CHA2DS2-VASc score to calculate the stroke risk for people with a. fib. A higher score is correlated with an increased risk of stroke, and the recommendation for anticoagulation is stronger. The CHA2DS2-VASc score considers other risk factors such as sex, age, diabetes, history of heart disease, hypertension, or stroke.
Surgical and Post-Surgical Applications
DVT is more common in people who have had abdominal or pelvic surgery or those who have had orthopedic surgeries such as hip or knee replacement. Anticoagulants are often used to prevent blood clots in these populations. Another way to prevent blood clots in these populations is mechanical devices that squeeze the legs.
Risks and Side Effects
Anticoagulants are effective for preventing and treating blood clots, but they also come with risks and side effects.
Common Side Effects
Some of the common side effects of anticoagulants include:
- Excessive bleeding
- Bowel changes
- Nausea or vomiting
- Indigestion
- Headaches
- Dizziness
- Itching
- Rashes
Many of the common side effects of anticoagulants do not require you to change or stop the medication, but it is important to discuss all side effects with your healthcare provider to ensure that there isn’t something more serious going on.
Serious Complications
Anticoagulants also have the potential for serious complications, such as bleeding from the digestive tract or bleeding in the brain.
According to one study in Therapeutic Advances in Gastroenterology, people who have significant gastrointestinal (GI) bleeding on anticoagulants are more likely to have other complications associated with anticoagulation, so monitoring closely for GI bleeding is important. The risk of major GI bleeding is 0.5-8.4 events per 100 patient years depending on the reason the patient is on anticoagulation. If you are having bloody or black stools, you should talk to your healthcare provider immediately.
Hemorrhagic stroke, or bleeding in the brain, is another serious complication that can be caused by anticoagulants. This risk is higher in people who have high blood pressure. Hemorrhagic stroke is the most serious complication of anticoagulants and carries a significant risk of death or disability. The risk of brain bleeding from anticoagulation is about 0.25-1.1% per year.
Contraindications and Precautions
Determining whether someone should or shouldn’t be on anticoagulation requires careful consideration of risks and benefits. You should never stop blood thinners without talking to your healthcare provider. That said, there are some people for whom anticoagulants are generally not recommended. These include people who have:
- active, significant bleeding
- very low platelet counts
- major trauma
- recent or planned significant surgeries with high bleeding risk
- tumors in the brain or spine
- recent epidural or spinal puncture
- severe high blood pressures
It is important to talk to your healthcare provider about all of your medication conditions and medications prior to starting an anticoagulant medication to ensure that you are taking them safely and appropriately.
Managing Anticoagulant Therapy
Some anticoagulant medications require careful monitoring and adjustment while others don’t.
Monitoring and Dosage Adjustment
Most patients on warfarin require careful monitoring to ensure that the blood is thinned enough but not too much. The level of anticoagulation is measured using the international normalized ratio or INR. INR is generally obtained by a finger poke or vein blood draw. The prothrombin time is measured and the INR is calculated.
The ideal INR is determined by your healthcare provider based on the reason for anticoagulation, but in general, the goal for INR is usually 2-3 or 2.5-3.5. Based on the INR level, the dose of warfarin may be adjusted up or down.
Drug Interactions
Anticoagulants have the potential to interact with a number of medications and even some foods. Warfarin has the most interactions, but DOACs also have the potential to cause interactions. There are over 500 interactions between warfarin and other medications, though many of them may not be clinically significant. Some of the common interactions for warfarin include:
- antibiotics
- foods that contain vitamin k
- nonsteroidal anti-inflammatories
- other blood thinners
- antifungals
- antivirals
- some cholesterol-lowering medications
- mental health medications
- chemotherapy
- herbs and supplements
DOACs also can interact with other medications. Your healthcare provider or pharmacist can help you determine if you need your medication adjusted or changed based on the potential interactions with other medications so it is important for you to discuss all medicaitos and supplements you take with your healthcare team.
Emergency Protocols
If you are experiencing severe bleeding while on anticoagulation, you should speak with your healthcare provider immediately or go to the nearest emergency department. Anticoagulation medications can sometimes be reversed if necessary. For example, warfarin can be reversed by administration of vitamin K. Other anticoagulants may require blood products such as fresh frozen plasma to reverse them.
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Key Takeaways
- Anticoagulants are lifesaving medications that can prevent blood clots and strokes
- Anticoagulants should be taken as directed and monitored closely by your healthcare team
- Bleeding with anticoagulants can be severe and life-threatening
- It is important to consider the risks and benefits of anticoagulants before starting and as risk factors change
- You should make sure your healthcare provider knows about all of the medications and supplements you take
Anticoagulants can significantly reduce your risk of blood clots and strokes when used in the right context. Your healthcare provider can help you determine if these medications are right for you.
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