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Drug Class: Commonly Known As: Category:
Anticoagulant Marevan® Adult

Warfarin - What is it for

Warfarin is an anticoagulant, sometimes called a "blood thinner”

Warfarin prevents clot formation and existing clots from getting bigger

Warfarin does not dissolve clots that have already formed as your body’s natural processes will dissolve the clots

We currently keep three strengths of warfarin as described below:

​Strength (mg)​Colour



Do not change brands as they may have slightly different effectiveness

Why are you taking Warfarin?

You are prescribed warfarin by your doctor for:

□ Existing clots in the lungs, veins, arteries or heart

□ Irregular heart rhythm

□ Heart valve replacements

□ Stroke

□ Others: _____________

  • To reduce the clotting ability of your blood thus preventing further complications
  • Duration of treatment may vary from 3-6 months to long term depending on your condition

Warfarin - Side Effects, Precautions, and Contraindications

What side effects can Warfarin cause?

  • Possible side effects of Warfarin include:
    • Unexplained nose bleed
    • Bleeding from gums when brushing teeth
    • Prolonged bleeding from minor cuts (10-15 minutes) despite applying pressure on wound. Action: Check with your doctor if the bleeding does not stop within 15 min or if you feel unwell
    • Excessive menstrual bleeding (women) Action: For women, increased menstrual flow is common but check with your doctror if you feel unwell.
    Serious side effects of warfarin overdose include:
    • Blood in urine or cloudy and dark urine
    • Black, sticky or tarry stool (not due to iron supplement)
    • Coughing up blood or coffee ground-like vomit
    • Unexplained large bruises or purplish area on skin
    • Sudden severe headache with nausea or loss of consciousness Action: Check with your doctor immediately or admit yourself to the Accident and Emergency Department (A&E) if you experience any of the symptoms or feel unwell

Before taking Warfarin , what precautions must I follow?

What food or medicine must I avoid when I take Warfarin ?

  • Effect of warfarin depends on the amount of Vitamin K in your body which is mostly derived from your diet
  • Eat a well-balanced diet while you are on warfarin
  • Ensure consistent and moderate consumption of Vitamin K rich food (Refer to the table at the bottom of this page)
  • Avoid making any MAJOR CHANGES to your diet (e.g. becoming a vegetarian) without first consulting your doctor or pharmacist
  • Avoid excessive alcohol consumption. It is advisable not to take more than 5 cans of beer or 1 bottle of wine per week
  • Avoid any form of traditional or herbal remedies and over-the-counter supplements (e.g. gingko, garlic, cordyceps and ginseng) as their effect on warfarin is unpredictable
  • Consult your doctor or pharmacist before you start or stop taking any medication or supplements. Certain medications like pain killers, antibiotics, and hormonal

Warfarin - Dosage and How to Use

How should Warfarin be used?

  • Warfarin can be taken with or without food
  • Take at the same time, once daily
  • DO NOT miss, double or adjust your dose unless directed by your doctor or pharmacist

What happens when you start Warfarin

  • You will be given a booklet called Anticoagulation Therapy Record that provides an ongoing record of your blood tests and warfarin dosage
  • Remember to bring the booklet with you every time you visit Anticogulation Clinic
  • Warfarin dose is adjusted according to your desired International Normalised Ration (INR) that measures the effectiveness of warfarin and its bleeding risk
  • Your desired INR range is: _____________________
  • Blood tests may be required more frequently to determine the appropriate warfarin dose
  • Your dose may change after each visit depending on your INR result. Your doctor or pharmacist will inform you any dose changes
  • Inform your doctor or pharmacist of any illnesses, hospitalisation, changes in medication(s) or lifestyle at your next appointment
  • Inform other healthcare professionals (doctors, dentist, pharmacist) whom you are seeing for other condition(s) that you are on warfarin

What should I do if I miss a dose?

  • Take it as soon as you remember if it is within 8 hours of your usual time to take warfarin
  • If it is after 8 hours, skip the dose for that day
  • Just take your warfarin dose at the usual time the next day
  • DO NOT take double doses, unless your doctor tells you to, as this can cause excessive bleeding
  • Record the dates on which you missed your dose(s). Inform your doctor at your next appointment

What should I do if I overdose?

Warfarin - Handling

How should I handle Warfarin safely?

Warfarin - Storage

How should I store Warfarin ?

;#Keep away from children;#Keep in a cool, dry place, away from direct sunlight;#Store at room temperature;#

How should I dispose of Warfarin safely?

Warfarin - Additional Information

What else do you need to know about warfarin?

  • Inform your doctor if you have not been eating well or feeling unwell (e.g. fever, vomiting, diarrhoea, infection)
  • Avoid intramuscular injection because it may lead to haematoma (bleeding in the muscle)
  • Ensure that you keep sufficient warfarin supply at all times especially if you need to travel
  • If you are pregnant or intending to get pregnant, please inform your doctor as warfarin may affect your foetus

Do you need to make any lifestyle changes?

  • No need to make any changes to your lifestyle. Keep it consistent and have a well-balanced diet.
  • Be extra cautious when handling razors or other sharp objects
  • Avoid contact sports or other activities that may cause you to be injured and lead to excessive bleeding

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