Anticoagulants for Stroke Prevention

Anticoagulants for Stroke prevention in aFib

Anticoagulants for stroke prevention IN AFIB

Preventing Clots with Medication (anti-platelets and anticoagulants)

Drugs such as blood thinners are given to patients to prevent blood clot formation or to treat an existing blood clot. Examples include

  • Aspirin
  • clopidogrel
  • Warfarin
  • Other FDA approved anticoagulants that do not require the monthly blood test, but care must be taken to take them as directed so that you receive the maximum benefit for stroke prevention.
    •  dabigitran,
    • rivaroxaban, and
    • apixaban:

Overview of Side Effects

Antiplatelets can increase your risk of bleeding. Even though aspirin can be purchased over the counter, it is important that you do not take more than the dose prescribed by your doctor. Report any of the symptoms stated below to your healthcare provider.

Anticoagulants increase risk of bleeding. If you are prescribed warfarin, there is a monthly blood test that is necessary to monitor and achieve optimal dosing. Read our patient’s guide to taking warfarin.

Important Precautions when taking anti-clotting medications

  • Call your healthcare provider right away if you have any unusual bleeding or bruising
  • If you forget to take your daily anticoagulant dose, don’t take an extra one to catch up! Follow your healthcare provider’s directions about what to do if you miss a dose.
  • Always talk to your healthcare provider about switching from one anticoagulant to another (including changing to a generic version). Even small variations in the amount of the dose of a medication can cause problems.
  • Always tell you doctor, dentist and pharmacist that you take one of these medicines. This is especially important before you start taking a new medication or have any procedure that can cause bleeding.
  • If you are taking warfarin, discuss any new medications with your healthcare providers.
  • It is also wise to take extra care with contact sports or any other situation that might risk unnecessary trauma.
  • Here are some things to watch for or report to your physician:
    • If you have an accident of any kind
    • If you often find bruises or blood blisters
    • If you feel sick, weak, faint or dizzy
    • If you think you are pregnant
    • If you notice red, dark brown or black urine or stools
    • If you bleed more with periods
    • Bleeding gums
    • Bad headache or stomach ache that won’t go away


  • Warfarin (Coumadin) is taken as a pill and is currently the most widely used blood-thinning medication.
  • Warfarin (Coumadin) reduces the ability of the blood to form clots and if clots are already present, warfarin helps to make these smaller or to disappear (dissolve).
  • A blood clot is formed by blood cells and other material sticking together to form a solid mass inside a blood vessel and clotting factors are needed to make this happen. Warfarin prevents some of these clotting factors from working, making the blood thinner, which means that less the blood is less likely to form blood clots.
  • Warfarin is very effective at reducing the risk of stroke in patients with atrial fibrillation. Compared to no treatment, warfarin prevents 2 out of 3 strokes.
  • In many countries, different doses of warfarin are available. The tablets are different colours to allow you to tell the difference between the different doses.


The INR is the International Normalised Ratio, a measure of how fast blood clots and this evaluates the effectiveness of warfarin in thinning your blood.
Your INR will be measured usually by pricking your finger to obtain a small droplet of blood which is put onto a special strip which can be analysed by a hand-held point-of-care device.

  • In people who are not taking a blood-thinning medicine, blood clots with INR of around 1.0. To reduce the risk of a stroke in atrial fibrillation the blood needs to be 2-3 times thinner than normal.
  • This means that the blood takes 2-3 times longer to clot.
  • If you have atrial fibrillation your target INR range will be 2.0 to 3.0.
  • If your blood is too thick (INR less than 2.0), then you are still at increased risk of having a stroke (caused by a clot).
  • If your blood is too thin (INR greater than 3.0), then this increases your risk of bleeding.
  • Some people attend a clinic (either at the hospital or their GP or health centre) to have their INR monitored. Other people self-monitor and/or self-manage their INR at home but this is not suitable or possible for all patients. If you wish to self-manage your INR you need to discuss this with your doctor.
  • When you first start warfarin it may be necessary to have your INR monitored every week but once your INR becomes therapeutic (in the INR range of 2.0 to 3.0) and is stable in that range, when you will only need to have INR checked every 4 to 6 weeks. Remember, it is very important to keep your INR in the recommended range of 2.0 to 3.0.



To help Warfarin work effectively, it is important to keep your vitamin K intake as consistent as possible. Sudden increases in vitamin K intake may decrease the effect of Warfarin. On

the other hand, greatly lowering your vitamin K intake could increase the effect of Warfarin.

To keep INR / PT stable and within the recommended range, it is important to:

  • take the correct dose of Warfarin at the same time every day
  • have your INR / PT checked regularly
  • keep your vitamin K intake consistent from day to day

To help make it easier to keep your intake of vitamin K consistent:

  • limit intake of foods considered “high” in vitamin K to no more than 1 serving each day
  • limit intake of foods “moderately high” in vitamin K to no more than 3 servings each day
  • report any significant changes in your diet or your weight to your doctor

In other words,

  • Watch how often you eat foods high in vitamin K.
  • Watch how much you eat of foods high in vitamin K

Vitamin K and Warfarin

Green leafy vegetables are among the best food sources of vitamin K. The average intake of vitamin K for most adults in the U.S. is 70 to 80 micrograms (mcg) per day. The Daily Value for vitamin K, an estimate of daily need, is 80 micrograms. The Percent Daily Values (%DV), listed on the tables below, help consumers determine if a food contains a little or a lot of a specific nutrient.

As indicated below, it is important to limit intake of foods that provide more that 60% of the Daily Value for vitamin K to help keep INR / PT in the desired range.

Foods high in Vitamin K (more than or equal to 200% DV)

Eat no more than 1 serving per day

Food                                                               Serving size                     % Daily Value

Kale, fresh, boiled                                     1/2 cup                                 660

Spinach, fresh, boiled                             1/2 cup                                  560

Turnip greens, frozen, boiled              1/2 cup                                   530

Collards, fresh, boiled                            1/2 cup                                    520

Swiss chard, fresh, boiled                     1/2 cup                                    360

Parsley, raw                                                 1/4 cup                                   300

Mustard greens, fresh, boiled             1/2 cup                                    260


Foods moderately high in Vitamin K (60 to 199% DV)

Eat no more than 3 servings per day

Food                                                              Serving size                           % Daily Value

Brussels sprouts, frozen, boiled             1/2 cup                                190

Spinach, raw                                                    1 cup                                   180

Turnip greens, raw, chopped                    1 cup                                   170

Green leaf lettuce, shredded                     1 cup                                   125

Broccoli, raw, chopped                                 1 cup                                  110

Endive lettuce, raw                                         1 cup                                      70

Romaine lettuce, raw                                     1 cup                                      70

Iceberg lettuce, red cabbage, asparagus, and soybean oil are often reported as being high in vitamin K. They contain much smaller amounts than foods listed in the tables above. These, and other foods and beverages not listed in the tables above (including coffee and tea), may be consumed as desired. Food Values are from the U.S. Department of Agriculture, Agricultural Research Service. 2003. USDA National Nutrient Database for Standard Reference, Release 16. Nutrient Data Laboratory Home Page,

What else should you know about Warfarin?


Alcoholic Beverages

Alcohol intake greater than 3 drinks daily can increase the effect of Warfarin. However, some medical doctors advise those taking Warfarin to avoid all alcoholic beverages. Check with your doctor about this issue.

One drink = 5 ounces wine

12 ounces beer

1 1/2 ounces liquor

Dietary supplements and herbal medications

Many dietary supplements can alter the INR/ PT. Dietary supplements known to affect the INR/PT include: arnica, bilberry, butchers broom, cat’s claw, dong quai, feverfew, forskolin, garlic, ginger, ginkgo, horse chestnut, insositol hexaphosphate, licorice, melilot (sweet clover) pau d’arco, red clover, St. John’s wort, sweet woodruff, turmeric, willow bark, and wheat grass.

Much is unknown about dietary supplements. The safest policy is for individuals on Warfarin to avoid all dietary supplements unless their physicians approve. This includes any vitamin/mineral supplements that list vitamin K on the label. If they are taken regularly on a daily basis, they pose less of a problem than if taken off and on.

Vitamin E supplements

Evidence suggests that vitamin E has blood-thinning effects. Vitamin E intakes above 1,000 International Units (IU) per day may increase the risk of excess bleeding. Research suggests that doses up to 800 IU may be safe for individuals on Coumadin®, but the evidence is not conclusive. It is best for those taking Warfarin to ask their physicians about taking Vitamin E supplements.


Some antibiotics can either lower vitamin K levels in the body or interfere with the activity of Warfarin. Check with your physician or pharmacist about whether you will need to adjust your vitamin K intake or Warfarin dose when you take antibiotics.


What are three important things to remember about Warfarin and vitamin K?

  1. Warfarin is a very important drug for you. Follow the prescription exactly, and keep your follow-up appointments for blood tests such as the INR/PT.
  2. Warfarin interacts with vitamin K in your body, so you need to keep vitamin K intake constant from day to day. It is also important to avoid herbal products and dietary supple­ments that may affect vitamin K and Warfarin unless approved by a qualified health care provider.
  3. Post the phone numbers of your doctor, pharmacist, and registered dietitian for ready reference when you have a question or concern about Warfarin, vitamin K, and your INR / PT.

Assessing your risk of bleeding with blood-thinning medicine

Click here for an online calculator

HAS-BLED- Bleeding risk scoring system
Risk factors


H -Hypertension (uncontrolled) Is your blood pressure more than 160 mmHg?


A – Abnormal kidney and/or function Do you have serious kidney problems such as renal failure, are you on dialysis, or have you had a kidney transplant?


Do you have abnormal liver function?


S – Stroke Have you ever suffered a stroke (even a mini-stroke)?


B – Bleeding Have you ever suffered any serious bleeding?


L – Labile INRs Are you on warfarin? (If your answer is no, then score 0). If you are on warfarin is your INR within the range of 2.0 to 3.0 most of the time? (If no, score 1)


E – Elderly Are you aged 65 or more?


D – Other prescription drugs and alcohol Do you take aspirin or pain-killers regularly together with a blood-thinning medicine?


Do you drink more than the recommended daily amount of alcohol?


Total maximum score possible



Your doctor will not prescribe a blood-thinning medicine if the risk of bleeding with such treatment outweighs the benefit of reducing your stroke risk.


Your blood-thinning medication may change over time as your risk of stroke changes, for example, as you get older, or if you are at risk of major bleeding by continuing to take a blood-thinning medication. Your doctor will discuss any changes that may need to be made to your medication as necessary.

There are also some situations when your doctor may alter the blood-thinning medication you take, for example, after a heart attack and/or when you have a stent fitted to open up a blocked artery in your heart. Your doctor will discuss any changes that may need to be made to your medication as necessary.

If you and your doctor decide that you would like to try to restore your heart rhythm from atrial fibrillation to the heart’s normal rhythm (known as “sinus rhythm”) then your doctor may suggest a controlled electric shock to the heart (known as ” electrical cardioversion”) or a specialist procedure known as “catheter ablation“. If you decide to have a cardioversion or an ablation procedure, you will need to take an anticoagulant drug for a period of time before and after the procedure to reduce the risk of a blood clot forming as a result of the procedure.
Surgery for atrial fibrillation may also be an option for some patients, with a procedure called surgical ablation or a Maze procedure. These procedures are usually only done in patients who are have heart surgery for another reason (for example, if you are having a heart valve replaced).



What are Newer oral anticoagulants?

Yes, there are currently 3 alternative blood-thinning medicines available for people with atrial fibrillation which can help to reduce the risk of stroke by thinning your blood.

Dabigatran (Pradaxa)
Rivaroxaban (Xarelto)
Apixaban (Eliquis)

These new medications have all been successfully tested on thousands of patients with atrial fibrillation and are effective and safe medications which can be used to prevent strokes.

The limitations of warfarin (interactions with food, other drugs and alcohol, and the regular blood tests to monitor the INR) have led to development of these new medications, with the aim to make them more convenient for patients to take than warfarin and at least as effective and safe.

These medications work by blocking the main clotting factors (factors in the blood which help it to clot), factor IIa (which is also called thrombin) (dabigatran) and factor Xa (rivaroxaban and apixaban). These new blood-thinning medicines block the clotting factor itself, not the vitamin K. This means that they work differently to vitamin K antagonists (for example warfarin and acenocouramol) and there are no restrictions on food if you are taking one of the new blood-thinning medicines. In addition, the way the body responds to these new medications is much more stable than with warfarin, so you do not need regular blood tests to measure the effectiveness of these new blood-thinning medicines, as you do with vitamin K antagonists such as warfarin and acenocoumarol.

All 3 medications, dabigatran (Pradaxa), rivaroxaban (Xarelto), and apixaban (Eliquis) are taken as a pill/tablet. Dabigatran (Pradaxa) and apixaban (Eliquis) are taken twice daily and rivaroxaban (Xarelto) is taken once daily. Unlike warfarin, these new blood-thinning medications do not require regular blood testing.

It is extremely important that you remember to take these new blood-thinning medicines as prescribed (once or twice daily depending on which medication you are prescribed) by your doctor to make sure that you get the protection against stroke that these drugs can offer. If you miss a dose you may be at increased risk of stroke.


Not necessarily. For many patients warfarin gives similar protection against stroke compared to the new drugs but the risk of serious bleeding in the brain (known as intracranial haemorrhage) is much less with the new drugs. However, the new blood-thinning medicines are not suitable for every patient with atrial fibrillation, particularly those with severe kidney or liver problems. Many patients are very happy and confident about taking warfarin and don’t mind the regular blood test checks. Recommendations on blood-thinning medications and their availability may vary from country to country. If you would like to discuss which blood-thinning medicine is most suitable for you, please seek advice from your doctor (hospital doctor or general practitioner).


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