Warfarin is a blood-thinning medicine that reduces the formation of harmful blood clots in your body. Blood clots can cause heart attack, stroke or other serious conditions.
This medicine is used to prevent and treat blood clots forming in the legs, lungs, heart and brain.
Take Warfarin exactly as directed by your doctor or according to the instructions on the label. Do not take more or less than instructed by your doctor.
You may take this medicine with or without food. Try to take it at the same time each day.
The dose of this medicine will be decided by your doctor. Your doctor will advise you on the treatment timeframe depending on the type and severity of your condition and your response to the medication.
Warfarin must be taken regularly for it to be effective. Continue taking this medicine even when you feel better. Do not stop taking it unless instructed by the doctor.
Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and return to your normal dosing schedule.
DO NOT double a dose under any circumstances.
If you often forget to take your medicine, let your doctor and pharmacist know.
Alert your doctor if you have the following conditions:
- bleeding problems or at risk of having bleeding problems e.g. active ulcers in the stomach or intestine, bleeding in the lungs, brain, genitals, urinary tract and stomach or intestine
- recent stroke caused by bleeding in the brain
- recent surgery in the eye, brain or spinal cord
- high blood pressure during pregnancy with or without fits or seizures
- severe high blood pressure
- have had a major surgery in the last 72 hours
- severe liver disease
as Warfarin may not be suitable for you.
Do not take this medicine if you are pregnant, planning to have a baby soon, or have given birth in the last 48 hours. If you become pregnant while being treated with Warfarin, alert your doctor immediately. This medicine may cause harm to your unborn child. You must use proven birth control methods while taking Warfarin and for at least 1 month after your last dose.
Do not take Warfarin with medicines used to dissolve blood clots, such as streptokinase and alteplase.
Inform your doctor if you have the following conditions:
- vitamin K deficiency
- protein C or protein S deficiency (disorders that may increase the risk of forming abnormal blood clots)
- history of bleeding in the stomach or intestine
- recent stroke due to blockage of blood vessels in the brain
- bacterial infection in the lining of the heart
- disease of the blood vessels supplying the brain
- high blood pressure not controlled by medicines
- serious heart problems
- thyroid disorder
- cancer
- anaemia (low red blood cell count in the body)
- diabetes
- polycythaemia vera (a blood disease that causes the bone marrow to make too many red blood cells)
- inflammation of the blood vessels
- kidney disease
- mild to moderate liver disease
Let your doctor know if you are breastfeeding.
Be sure to check with your doctor or pharmacist before giving Warfarin to the elderly or debilitated individual (physically or mentally weak, usually due to illness or old age). Elderly people and debilitated individuals may be more sensitive to the side effects.
If you are going to have an operation, such as minor surgery or dental work, inform your doctor or dentist that you are taking this medicine.
Some genetic traits (
CYP2C9 and
VKORC1) can affect an individual's response to this medicine or may increase the risk of serious side effects. Your doctor may perform genetic testing before giving you this medicine to know if it is suitable for you.
Why do I need to have blood tests done so often?
For as long as you are taking Warfarin, you will need to have regular blood tests to check your body's response to the medicine. This blood test is called an INR (International Normalised Ratio). The INR measures how much time your blood takes to clot. Each person has his or her target INR result. Your doctor will discuss with you your target INR result.
You will need to have an INR blood test done more often in the first few days or weeks. Your doctor needs to monitor your response to this medicine so that a suitable dose can be customised for you.
Why is it important to keep my appointments with the doctor?
Keep your appointments with your doctor. Your doctor needs to monitor your condition and check your response to the medication regularly.
- Pregnancy tests must be done before treatment to know if this medicine is suited for you to take.
- Regular monitoring of signs and symptoms of bleeding may also be needed.
What lifestyle changes can I make to improve my condition?
If you are a smoker, you should try to quit smoking. Smoking is harmful to your blood vessels and overall health. It has been shown that smoking will make your condition worse. Speak to your doctor or pharmacist about ways to stop your smoking habit.
Regular exercise will help to gradually improve your condition by improving your blood circulation. However, you should not over-exert yourself. Speak to your doctor about what type of exercise would be suitable for you.
You should also keep an eye on your cholesterol levels. Cholesterol build-up in the arteries can reduce blood flow and make the arteries stiff and narrow. Stick to a healthy, low-fat diet that includes lots of fresh fruits and vegetables.
Warfarin may cause any of the following side effects: nausea, vomiting, diarrhoea, stomach wind, bloating, abdominal pain, fever, chills, itching, hair loss, and rash.
Some side effects may need immediate medical help. Alert your doctor quickly if you experience any of the following:
- unusual bruising, nosebleeds, bleeding gums, bleeding from cuts that take a long time to stop
- coughing up blood, passing out bloody or black as tar stools and vomiting blood or ground coffee-like material
- pain, colour, or temperature change in any area of the body
- pain or difficulty in passing urine, change in how much urine is passed, blood in the urine
Inform your doctor if any of these side effects do not go away or are severe, or if you experience other side effects.
Do not take Warfarin with medicines used to dissolve blood clots, such as streptokinase and alteplase.
Inform your doctor and pharmacist if you are taking any of these medicines:
- other blood-thinning medicines e.g. heparin, aspirin, clopidogrel
- certain medicines for depression e.g. fluoxetine, fluvoxamine, sertraline
- NSAIDs (medicines for pain and inflammation) e.g. ibuprofen, celecoxib, phenylbutazone
- medicines to treat fungal infection e.g. fluconazole, ketoconazole
- medicines for epilepsy (fits or seizures) e.g. phenytoin, carbamazepine
- medicines for HIV infection e.g. atazanavir, fosamprenavir, nevirapine
- medicines for cancer e.g. capecitabine, imatinib, mercaptopurine
- cholesterol-lowering medicines e.g. fluvastatin, colestyramine
- certain antibiotics e.g. ciprofloxacin, metronidazole, clarithromycin
- rifampicin (medicine to treat TB, a lung infection known as tuberculosis)
- azathioprine (medicine used in organ transplants or certain immune disorders)
- zafirlukast (asthma medicine)
- St. John's wort (herbal medicine)
This list does not include all medicines that may interact with Warfarin.
Always notify your doctor and pharmacist if you are taking any other medicines, including herbal tonics such as traditional Chinese medicines, supplements, and medicines that you buy without a prescription.
Avoid alcohol.
Avoid excessive consumption of cranberry juice or cranberry products.
Avoid taking unusually large amounts of food that is high in vitamin K, such as dark green vegetables, beef or pork liver, and green tea. However, if it is your usual habit to take these foods, you may continue to do so. The key is to avoid sudden or drastic changes to your usual diet.
Store in a cool, dry place away from the reach of children.
Protect from moisture and light.
Medicines must not be used past the expiry date.
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