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Warfarin

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Why am I on warfarin?

Blood clots do not normally develop within our blood vessels but certain medical conditions may increase the risk of clot formation. Anticoagulants like warfarin are used in such situations to lower the clotting risk.


Daily doses are based on blood tests and varies from person to person. Combinations of warfarin tablets of different strengths may be prescribed for you.

What are the warfarin tablets that are available?

The brand name of warfarin is MAREVAN?. There are 3 strengths:

1 mg: brown tablet. 3 mg: blue tablet. 5 mg: pink tablet.


There are other brands of warfarin tablets available that are non-interchangeable. Thus it is important to recognize (e.g. colour) and know the strength of the warfarin that has been prescribed to you.

What do I do if I miss a dose?

Take warfarin at the same time daily. If you forget, take it as soon as possible (within 6-8 hours from your usual dosing time). After that time frame, skip the dose and take your usual dose the next day but do not double your dose. Diary the dates which you missed your dose and inform you doctor or pharmacist at your next appointment.


You may want to keep a record of each dose you take by marking it off on a calendar. In that way, you can also note which days you have missed a dose.


Contact your doctor or pharmacist for advice and book an earlier appointment if more than one dose is missed within a week.

What if I am travelling overseas?

Ensure that you have ample supplies of warfarin to last you for the entire period of your travel. For further advice on time difference and other dosing matters, speak to your Pharmacist.

Why do I need regular blood tests?

You will be monitored either at the Anticoagulation Clinic (ACC) or at your doctor’s clinic.


INR is used to measure the “thinness” of your blood. Regular blood tests are necessary to maintain your INR in the target range. Your warfarin dose would then be personalised by your pharmacist or doctor based on your INR results.


Initially, you may need more frequent blood tests (eg. once every one to two weeks) so as to adjust your dose of warfarin. However, once your INR readings are more stable, you will need less frequent testing.

What happens if I have to take other medicines and supplements?

Other medicines or vitamin supplements, including over the counter (OTC), herbal preparations or traditional medicines, can affect the action of warfarin. Please check with your pharmacist or doctor if you wish to take other medication and/or supplements.


Consult the pharmacist whenever you purchase OTC products and supplements. Should you be visiting a different hospital’s pharmacy, do inform the pharmacist there that you are on warfarin so that any interacting drugs can be avoided.


If you are seeing any other doctor or dentist, remember to inform them that you are taking warfarin.

Are there any special changes I need to make to my diet?

Vitamin K promotes blood clotting. Large variations in the vitamin K content from your diet will affect the action of warfarin. The larger the amount of vitamin K in your diet, the higher the dose of warfarin needed. However, there is no need to change your diet or avoid certain food due to its vitamin K content, as some of them such as dark green leafy vegetables contribute to a healthy diet. What is important is for you to follow a balanced and consistent diet, eat a variety of food types and keep to your normal routine. Do not make drastic changes to your usual diet and avoid bingeing on foods high in vitamin K. Refer to the diet table given to you for details.


Avoid consuming alcohol. On certain social occasions such as festivals and weddings, try to limit your intake of alcohol to one glass of wine or its equivalent.

What sort of precautions do I need to take?

Should you have prolonged periods (more than 3 days) of fever, vomitting and diarrhoea, seek medical attention. Note also the dates and report them to your pharmacist or doctor on the next visit for a blood test.


Warfarin may increase the risks of bleeding and bruising. Some warning signs to look out for include nosebleeds, gum bleeding and heavy menstruation. It may be necessary to switch to a soft-bristled toothbrush. Should you experience these side effects, please inform your doctor or pharmacist as soon as possible.


Examine yourself daily for any bruises and pin-sized blood spots under the skin. Do not massage any bruises.


Certain contact sports and activities like rugby and judo should be avoided as they can put you at greater risk of injuries and bruising.


If you have had a hard fall or are hit with a huge impact by some object, report immediately to A&E to exclude any internal bleeding.


Inform your doctor immediately if you develop extensive bruising (especially in the absence of trauma) or if a minor cut continues to bleed after applying continuous pressure for more than 15 minutes.


It is also useful to carry an identification card stating that you are on warfarin, in case you get into accidents and are unconscious.


Should you be undergoing any sort of invasive procedures e.g. operations (surgery) or dental procedures, check with your doctor to see if there is a need to stop or lower the dose of the warfarin you are taking. Should your doctor agree to stopping or lowering warfarin, make an appointment with the anticoagulation clinic pharmacist at least a week before your procedure.

When is it critical that I go to a doctor immediately?

It is important that you have sufficient supply to last until your next appointment. If you realise that you are running out of supply before your appointment, either bring forward your appointment or call up the clinic to get a further prescription for more medicine to last until your appointment date.


Go to the A&E immediately when you experience/notice the following :

  • Coffee-grain like appearance of vomit
  • Dark, cloudy or “Teh-O”-coloured urine
  • Dark, tarry and odourous stools
  • Extensive bruising or hard impact(s) occurring to any part of your body
  • Severe bleeding that does not stop despite application of continuous pressure for more than 15 minutes
  • Sudden shortness of breath
  • Increased frequency of chest tightness or chest pains
  • Sudden blurred vision (“blackouts”), severe headaches with nausea and vomiting or memory lapses
  • Numbness and/or weakness over one side of your body
  • Sudden development of red, swollen, warm and painful lower limb(s)

In addition, please consult your doctor immediately should you suspect you are pregnant. You should also consult your doctor before conceiving or deciding to breastfeed.






- Last updated 4 Aug 2010,2:11 pm




The content of this website is provided for general informational purposes only and is not intended as, nor should it be considered a substitute for, professional medical advice. Do not use the information on this website for diagnosing or treating any medical or health condition. If you have or suspect you have a medical problem, promptly contact your professional healthcare provider.

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