What it does

Warfarin is an anticoagulant drug. It is used to prevent the formation of blood clots in the veins of people who are more susceptible to their formation, by interfering with the clotting process. These clots could otherwise block the blood flow to important organs.

Warfarin treatment is essential for people with mechanical heart valves to ensure that clotting of the valve is prevented.

General Information

Since clotting is the way in which the body stems blood flow from an injury, a fine balance must be achieved and over dosage can lead to bleeding from the nose, gums or in the urinary tract. The dosage therefore needs to be carefully calculated using the results of regular blood tests. These blood tests measure the degree of anticoagulation (thinness of the blood). The results are expressed as a value known as the INR (prothrombin ratio) - a value of 2 to 3 is aimed for (a value of less than 1,5 means that the blood clots too easily ; a value of more than 3,5 means that the patient bleeds too easily).

The Warfarin dose is adjusted until the ideal value is achieved. The dose required to produce this value differs from patient to patient, therefore it is important to take your tablets exactly as prescribed for you. If possible, take the prescribed dose at the same time/s each day. If you miss a dose, make a note of the date and tell your doctor when you next have a blood test. If you miss more than one dose, ask your doctor for advice.

Do not take an extra dose of Warfarin.

Do not stop your Warfarin tablets without consulting your cardiologist.

Frequent diarrhoea, a prolonged fever or pronounced dietary changes may alter the body's response to Warfarin and it is advisable to inform your doctor should any of these occur.

Alcohol may increase or decrease the effect of Warfarin, so limit your intake of alcohol. Try to avoid activities that have a high risk of injury. The use of Warfarin may need to be stopped (or the dose reduced) before surgery, including dental surgery. This should be discussed with your doctor/dentist.

Warfarin should not be taken during pregnancy.

Possible side effects

  • Bleeding - Inform your doctor immediately should you notice any excessive bruising, very dark brown or black stools, blood stained urine or unusual bleeding such as bleeding from the gums or nose.
  • Nausea and vomiting - This occurs infrequently.

Interaction with other medication

A wide variety of drugs interact with Warfarin either by increasing or decreasing the anti-clotting effect, therefore no medication should be taken without consulting your doctor or pharmacist.

Some non-prescription drugs that interact with Warfarin:

  • Aspirin (e.g. Disprin).
  • Chloroquine (found in malaria tablets).
  • Liquid paraffin (found in many laxatives).

Some prescription drugs that interact with Warfarin:

  • Certain antibiotics.
  • Oral contraceptives.
  • Cortisone tablets.
  • Certain drugs used for gout.

It is a good idea to wear a medic alert bracelet to advise others that you are taking Warfarin.