Warfarin is a blood-thinning medicine. It prevents special cells in the blood from sticking to each other. This reduces the risk of harmful blood clots forming in your body. Blood clots that form in a blood vessel inside the brain or in a vessel leading to the brain can cause a stroke.
This medicine is used to prevent or treat pulmonary embolism (blood clots in a lung artery). It is also used to prevent clotting in the heart due to irregular heartbeats.
Warfarin is also used to prevent blood clots in people with artificial heart valves or those with faulty heart valves. This medicine may also be used to treat other conditions such as blood circulation problems in the leg or heart.
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 Warfarin 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.
This medicine must be taken regularly for it to be effective. Continue taking Warfarin even when you feel better. This medicine is not a cure for your condition, and you may need to take it for an indefinite length of time. Do not stop taking Warfarin 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:
- risk of serious bleeding e.g. recent brain or spinal injury
- stomach ulcers, especially if you have bled from a stomach ulcer
- high blood pressure that is severe or not well-controlled
- blood disorders
- recently had surgery or operation
as Warfarin may not be suitable for you.
Do not take Warfarin if you are pregnant or planning to have a baby soon. If you become pregnant while being treated with this medicine, alert your doctor immediately. Warfarin may cause harm to your unborn child. You must use proven birth control methods while taking this medicine. You may wish to discuss birth control methods with your doctor.
Do not take Warfarin with any other blood-thinning medicines, such as streptokinase and alteplase.
Inform your doctor if you have the following conditions:
- liver disease
- kidney disease
- vitamin K deficiency
- systemic infection
- thyroid problems
- active tuberculosis
- heart disease
- diabetes
- risk of falling
- open wound
- have indwelling catheter
- history of peptic ulcer disease
- low red blood cell count in the body
- recently gave birth
Let your doctor know if you are breastfeeding.
Do not take part in activities in which you may fall or get injured, such as contact sports. Alert your doctor if you get any unusual bruising (large bruises or several bruises) or bleeding that takes a long time to stop (e.g. too much bleeding when you floss or brush your teeth).
Take special care when shaving or handling sharp objects to avoid cutting yourself. Use a soft toothbrush when brushing your teeth to reduce the risk of gum bleeding.
Carry identification stating that you are on Warfarin. Most hospitals and clinics will be able to provide you with such identification. Speak to your doctor about this.
Be sure to check with your doctor or pharmacist before giving this medicine to the elderly. Elderly people may be more sensitive to the side effects.
If you are going to have an operation, including minor surgery and dental work, inform your doctor or dentist that you are taking this medicine.
Some genetic traits (
CYP2C9 and
VKORC1) can affect your response to Warfarin and may increase your risk for serious side effects. Your doctor may perform genetic testing before giving you this medicine or during the early days of your therapy, to check if the dosage is suitable and effective 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 own target INR result. Your doctor will discuss with you about 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 for signs of bleeding may also be needed.
Your doctor will advise you about how often you will need to have these tests.
Warfarin may cause any of the following side effects: hair loss, rash, fever, diarrhoea, nausea, and vomiting.
Some side effects may need immediate medical help. Alert your doctor quickly if you experience any of the following:
- unusual bleeding, especially excessive bleeding or bleeding that takes a long time to stop
- gum or nose bleeding that takes a longer than usual time to stop
- unusual bruises, especially if the bruises appear by themselves or if they cover a large area
- heavier than usual menstrual flow or any other changes in the menstrual flow
- nausea, vomiting, diarrhoea, fever or other signs of infection that last for 2 days or more
- sticky, black or bloody bowel
- blood in the urine (this usually shows as a dark tea colour)
- coughing out blood or phlegm that looks like coffee grounds
- severe dizziness with tiredness, fever, headache and body pain
- chest pain
- difficulty breathing
- severe headache with nausea or vomiting or confusion
- swelling, pain or tenderness in the abdominal area
- purple discolouration of the skin, especially around the toes, feet and legs
- yellowing of the skin, eyes, pain near the stomach area
You should also alert your doctor if you fall or injure your head or back, or if you have any severe or prolonged back pain that has no obvious cause.
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 any other blood-thinning medicines, such as streptokinase and alteplase.
Inform your doctor and pharmacist if you are taking or have taken any of these medicines:
- other blood-thinning medicines as e.g. aspirin, ticlopidine, clopidogrel, cilostazol, dipyridamole
- medicine for gout (high uric acid level in the blood) e.g. allopurinol
- medicines for irregular heartbeat e.g. amiodarone, propafenone
- medicines to treat fungal infections e.g. itraconazole, fluconazole
- antibiotics e.g. erythromycin
- medicine to treat TB (lung infection known as tuberculosis) e.g. rifampicin
- medicines for epilepsy (fits or seizures) e.g. phenytoin, carbamazepine
- medicines for pain and inflammation (NSAIDs) e.g. diclofenac, mefenamic acid, ibuprofen
- cholesterol-lowering medicines e.g. fluvastatin, atorvastatin, gemfibrozil
- multivitamins containing vitamin K
- 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 and cranberry juice.
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.
Medicines must not be used past the expiry date.
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