Warfarin belongs to a group of medications known as anticoagulants, designed to prevent the extension of existing blood clots and/or formation of new blood clots. Conditions like Atrial Fibrillation, Deep Vein Thrombosis, Pulmonary Embolism and Cardiac Thrombus will require the use of warfarin.

​​​​​​What is this medication used for​

Warfarin belongs to a group of medications known as anticoagulants, designed to prevent the extension of existing blood clots and/or formation of new blood clots. Conditions like Atrial Fibrillation, Deep Vein Thrombosis, Pulmonary Embolism and Cardiac Thrombus will require the use of warfarin.

Daily doses are based on blood test results and vary from person to person. Combinations of warfarin tablets of different strengths may be prescribed. 

Dosage and How to Use​

Take warfarin consistently at the same time every day, with or without food.

Missed a Dose​​

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. 

Write down the dates which you missed your dose and inform your 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 daily. ​

Side Effects, Precautions, Contraindication​​

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 magnify or reduce the effects of warfarin. Please check with your pharmacist or doctor if you wish to take other medication or supplements.

Should you be visiting a different hospital’s pharmacy, 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 changes in vitamin K content from your diet will affect 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. 

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 are some of the side effects of Warfarin?​

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

Warfarin may increase risk of bleeding and bruising. Some bleeding signs to look out for include nosebleeds, heavy menstruation, or gum bleeding. It may be necessary to switch to a soft-bristled toothbrush to reduce gum bleeding. 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 as it may worsen the bruising.

What sort of precautions do I need to take?​​

Certain contact sports and activities like rugby and martial arts e.g. karate/judo should be avoided as they can put you at greater risk of injuries and bruising. 

Should you be undergoing any invasive procedures e.g. operations/surgery or dental procedures, check with your doctor if there is a need to stop warfarin. 

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 request for a prescription for more medicine. Missing more than one day’s medicine could result in undesired consequences, such as the loss of Warfarin’s effects.

Handling and Storage​​​

Keep the tablets in a safe place out of reach of children. Store the tablets in a dry place at room temperature, away from heat and direct light. ​


When to seek further medical advice​

Look out for signs of allergy: swelling of lips and/or eyes, difficulty breathing, rashes or itching. Stop the medication and see your doctor immediately if it occurs.

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

Go to the Accident and Emergency (A&E) department immediately if you experience/notice the following:

  • ​Coffee-grain like appearance of vomit;
  • Dark, cloudy or “Teh-O”-coloured urine;
  • Dark, tarry, and foul-smelling stools;
  • Extensive bruising or hard impact(s) occurring to any part of your body;
  • Severe bleeding that persists despite applying 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;
  • Numbness and/or weakness over one side of your body;
  • Sudden development of red, swollen, warm and painful lower limb(s)


Additional Information​

What are the warfarin tablets that are available?​

The brand name of warfarin is MAREVANÒ. There are three strengths:

1 mg: brown tablet.
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 and know the strength of the warfarin that is prescribed. 

Why do I need regular blood tests?​​

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

International Normalized Ratio (INR) is used to measure the clotting ability 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 (e.g. once every 1 – 2 weeks) to adjust your warfarin dose. Once your INR readings are more stable, you will require less frequent testing.​


Prepared by KTPH Patient Education Workgroup 08.05.17
The information provided in this article is intended to supplement, not as a substitute for, the expertise and judgment of your doctor, pharmacist or any other healthcare professional. ​

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