Anticoagulation Therapy

Anticoagulants are a type of drug that reduces the body's ability to form clots in the blood. They do this by inhibiting the production of vitamin K in the liver. This increases the time your blood takes to clot. Although they are sometimes called blood thinners, they do not actually thin the blood. This type of medicine will not dissolve clots that already have formed, although it will help to stop an existing clot from getting larger.

Why you may need anticoagulants

You may need to take warfarin, or other anticoagulants, if you have been diagnosed with or treated for one or more of the following:
  1. Atrial fibrillation (AF)
  2. Artificial heart valve
  3. Deep vein thrombosis (DVT)
  4. Pulmonary embolism (PE)
  5. Prevention of blood clots e.g. genetic clotting disorders
  6. Stroke
  7. Heart Attack
Sometimes it is only necessary to take anticoagulants for a few months. In other circumstances you will take them for life. Your health care professional will tell you how long to take them for. Do not stop taking them unless you are told to you.

Anticoagulant drugs affect the blood's ability to clot and therefore there is an increased risk of bleeding for people who are taking them. Because of this risk, it is vitally important to take the tablets exactly as directed. Never take larger or more frequent doses.

How will my treatment be monitored?

Your treatment is monitored by regular blood tests. The result of the blood test will be recorded in your Anticoagulant Therapy Record Book, or on a print out from a computer. Your warfarin dosage will be adjusted up or down depending on the result of your blood test: If you are within your therapeutic range your dose will not be altered. If the INR is too low, the warfarin dose is increased; if it is too high the dose is decreased. No two people are the same and you may need a higher or lower dose than someone else to achieve the same result. You will need to have regular blood tests to check the blood's clotting ability. The results of these tests will help your Doctor determine the proper dose of the drug to be taken each day. The test result may be referred to as your INR.

What does INR mean?

It stands for International Normalised Ratio (INR) and is a measure of how much longer it takes the blood to clot when oral anticoagulation is used. For example, if your INR is 2 the blood is taking twice as long as normal to clot. Everyone needs a unique dosage of anticoagulant, which needs to be kept at a stable level. You will be given a therapeutic range this will vary depending on the condition for which you are taking anticoagulants. Within that range you will have a target INR. For example if your therapeutic range was 2 to 3 then your target INR would be 2.5. It is important to keep within your therapeutic range. If your result is above that range then you are at an increased risk of bleeding and if your result is lower than then you are at an increased risk of clotting. People who are taking anticoagulant drugs should tell all doctors, dentists, pharmacists, and other medical professionals who provide medical treatments or services to them that they are taking this medicine. They should also carry identification stating that they are using an anticoagulant drug. Do not take any other prescription or over-the-counter medicine (especially aspirin) without first telling the Pharmacist that you are taking anticoagulation therapy. This also applies to medicines that you may think of harmless such as cough medicine.

Is the treatment safe?

Anticoagulant therapy is safe as long as you follow the advice of your anticoagulant clinic and/or the advice in your Anticoagulant Therapy Record Book. You will need to have your blood tested at regular intervals. Your INR reading may vary, but will need to be kept within a certain range decided by your GP or consultant.

Are there any side effects?

The most common side effects of warfarin are bleeding and bruising. This will normally occur when you go out of your therapeutic range. However sometimes bleeding can occur when you are still within range. It can be in the form of prolonged bleeding from cuts, bleeding that does not stop by itself, nose bleeds, small or large bruises under the skin, bleeding gums when brushing the teeth, red or dark brown urine, red or black stools, or coughing or vomiting bloodstained fluid. Any of these should be reported to your clinic. In the event of prolonged bleeding, you must inform your GP or haematologist, or go to the nearest casualty department for urgent treatment.

The newer oral anticoagulants have been reported as having fewer side effects, and to cause less bleeds. You would need to discuss these new drugs with your doctor to find out if they may be suitable for you.


Anticoagulants. NMIHI. Accessed at

Atrial fibrillation. NMIHI. Accessed at

Deep Vein Thrombosis. MedlinePlus. Accessed at on January 28, 2018.

Heart Attack. Symptoms and causes. MFMER. Accessed at on January 29, 2018.

Pulmonary embolism. NMIHI. Accessed at

What are Anticoagulants? Accessed at on January 29, 2018.