HEALTHNET

Knowing more about drug: Warfarin (Part 1)

Warfarin is an oral anticoagulant drug and sometimes called blood thinners.

(Posted on 18 October 2007)

What is warfarin?

Warfarin is an oral anticoagulant drug and sometimes called blood thinners. It reduces the clotting ability of blood and prevents the formation of harmful blood clots in blood vessels which cause embolism. Warfarin can be used for conditions such as pulmonary embolism, venous thrombosis, atrial fibrillation, stroke and rheumatic heart disease.

Doctor will adjust the dosage of Warfarin to an appropriate clotting index (INR) for each patient to control the clotting ability while preventing the formation of harmful clots in blood vessels. Moreover, doctors will also perform blood test with patients regularly to check the clotting index and may adjust the dosage if required.

Side effects of taking warfarin

The most common side effects from taking Warfarin is bleeding and, therefore, patients should pay extra attention to any symptoms related to bleeding. When there is severe or persistent bleeding, patients should consult a doctor immediately. Examples are more than usual bleeding when brushing teeth, nonstop bleeding after being cut, unexplained bruising and nonstop nose bleeding, etc. The symptoms of internal bleeding include vomiting or coughing up blood, black stools or blood in the stools, red or dark brown colored urine or blood in the urine, unusually heavy menstrual bleeding, persistent or severe headaches, dizziness, blurred vision, confusion in speech, weakness, and abdominal pain or swelling.

Patients should take the medication regularly according to doctor's instruction. Do not increase/decrease dosage or stop taking the medication on their own initiative, as it will affect the anticoagulant activity or increase its side effects of bleeding. Warfarin may have an adverse effect on the fetus so a patient should inform her doctor immediately if she is pregnant or planning to become pregnant.

Interaction of warfarin with other drugs

Warfarin interacts with many drugs (such as Aspirin) which will affect its anticoagulant activity or increase its side effect of bleeding. Therefore, patients should consult their doctor or pharmacist before taking any other drugs (including nonprescription drugs). Warfarin may also interact with many Chinese medicines or herbs such as red sage root, Chinese angelica root, red peony root, and St. Johns Wort. Patients should not take Chinese medicines or herbal medicines as and when they wish, including soup and food with Chinese medicines or herbal ingredients.

In our next issue, we will talk about specific things that need attention in the diet and daily lives of patients who take Warfarin.

Source: Hong Kong and Drug Education Resources Centre, The Society of Hospital Pharmacists of Hong Kong