Warfarin - Things to consider when taking warfarin

People with certain health conditions should avoid warfarin. Anyone taking warfarin will also need to have their dose monitored.

Monitoring your dose

While you are taking warfarin, you will need regular blood tests at your GP surgery or local anticoagulant clinic. This is to make sure that your dose is correct.

How well your warfarin is working is measured using the international normalisation ratio (INR). This measures how long it takes your blood to clot. The results of your INR tests determine the dose of anticoagulant you need to take.

• If your INR is too high – blood clots will not form quickly enough and you may experience bruising or you may be at increased risk of bleeding. In this case, your dose may need to be reduced.
• If your INR is too low – your medication is not working sufficiently, which means that clots could still form unnecessarily and block a blood vessel. In this case, your dose may need to be increased.

When you first start taking warfarin, your INR will be tested within the first three to four days of starting treatment. Depending on your results, further tests will be carried out once or twice a week. If your INR stabilises within the correct range, testing will become much less frequent.

Once your INR levels are stable, you may be shown how to use a self-testing machine, which can be used to measure your own INR at home. This can also be useful if you are going on holiday, for example.

Tablet strengths

It is important that you are familiar with the different strengths and colours of these tablets and know which tablets you need to take to make up your dose.

In the UK, the strengths and colours of warfarin tablets are:

• 0.5mg – white tablets
• 1mg – brown tablets
• 3mg – blue tablets
• 5mg – pink tablets

Warfarin is taken once a day, usually in the evening. It is important to take your dose at the same time each day with or without food.

Read information about what to do if you miss a dose or take an extra dose of warfarin.

When to avoid warfarin

Warfarin should be avoided if you have:

• uncontrolled severe hypertension (high blood pressure)
• had a recent stroke
• a risk of bleeding inside the body – for example, if you have recently had major surgery or an organ biopsy, or if you have a peptic ulcer
• a bleeding disorder, such as haemophilia (a blood clotting disorder), liver failure or kidney failure

Warfarin should also be avoided if you are pregnant (see below).

Using warfarin with caution

Warfarin should be taken with caution if you have a high risk of falls – for example, if you are elderly or have recently had surgery.

You should avoid high-impact sports, such as rugby or martial arts, which carry a risk of serious injury, particularly head injuries. Any bleeding or bruising while taking warfarin will be worse than usual.

You should also be aware of how warfarin interacts with certain foods, alcohol and other medications.

Pregnancy and breastfeeding

Warfarin can affect the development of a baby in early pregnancy, so it is not routinely used during pregnancy.

If you are already taking warfarin and think you may be pregnant, speak to your GP urgently.

You can usually take warfarin when you are breastfeeding. However, discuss this with your GP or midwife.