Warfarin

Common Brand Names

Maforan, Warf, Coumadin

Overview

Warfarin is a type of medicine known as an anticoagulant.

It makes your blood flow through your veins more easily. This means your blood will be less likely to make a dangerous blood clot.

Warfarin is used to treat blood clots and help prevent future blood clots if you've had one previously, such as:

• a blood clot in the leg (deep vein thrombosis, or DVT)
• a blood clot in the lungs (pulmonary embolism)
• It's also used to prevent blood clots if you're at high risk of having them in the future.

This includes people with:

• an irregular heartbeat (atrial fibrillation)
• a replacement or mechanical heart valve
• a blood clotting disorder, such as thrombophilia
• a higher chance of having a blood clot after an operation

Warfarin is only available on prescription in some countries.

Important Facts

• You'll usually take warfarin once a day in the evening.
• The most common side effect of warfarin is bleeding more easily than normal, such as having nosebleeds, bleeding gums, heavier periods and bruising. This is most likely to happen if you're unwell.
• You need to have blood tests at least every 12 weeks while you're taking warfarin to make sure your dose is right.
• It's normal for your warfarin dose to go up or down. The dose can depend on lots of different things, including what you eat and drink, what other medicines you're taking, and if you become unwell.

• Your doctor or pharmacist may give you an anticoagulant alert card. Always carry this with you. Show it to your doctor or dentist before you have any medical or dental procedures, including vaccinations and routine appointments with the dental hygienist. 

Side effects

Bleeding and what to do about it

While warfarin has enormous benefits, the downside is that it can make you bleed more than normal. This is because while you're taking warfarin, your blood will not clot as easily.

Apart from the risk of bleeding, warfarin is a very safe medicine. It's safe to take for a long time, even many years.

Less serious bleeding

It's usual to bleed more easily than normal while you're taking warfarin.

The kind of bleeding you might have includes:

• bleeding for a little longer than usual if you cut yourself
• occasional nosebleeds (that last for less than 10 minutes)
• bleeding from your gums when you brush your teeth
• bruises that happen easily and take longer than usual to fade

This type of bleeding is not dangerous and should stop by itself. If it happens, keep taking warfarin, but tell your doctor if the bleeding bothers you or does not stop.

Things you can do to help yourself:

• Cuts – press on the cut for 10 minutes with a clean cloth.
• Nosebleeds – sit or stand upright (do not lie down), pinch your nose just above your nostrils for 10 to 15 minutes, lean forward and breathe through your mouth, and place an icepack (or a bag of frozen peas wrapped in a tea towel) at the top of your nose.
• Bleeding gums – try using a soft toothbrush and waxed dental floss to clean your teeth.
• Bruises – these are harmless, but can be unsightly. It might help them fade more quickly if you put an ice pack wrapped in a towel over the bruise for 10 minutes at a time several times a day.

What you can do to prevent bleeding

While you're taking warfarin, be careful when you do activities that might cause an injury or a cut or bruising.

It can help to:

• avoid playing contact sports or other activities that can cause an injury, such as football, rugby, hockey and horse riding
• wear gloves when you use sharp objects like scissors, knives and gardening tools
• stop wet shaving or removing hair with wax – use an electric razor or hair-removing cream instead
• take false teeth (dentures) or retainers out for a few hours a day, if you wear them, to give your gums a rest – do not wear dentures or retainers that do not fit properly
• tell your doctor, dentist or nurse that you take warfarin before you have any medical or dental procedures or surgery – this includes vaccinations and routine appointments with the dental hygienist

Other common side effects

These side effects are usually mild. There are things you can do to help cope with them:

• A mild rash
• Hair loss

Talk to your doctor or pharmacist if these side effects bother you or do not go away.

Serious side effects

Serious bleeding

Occasionally, you can have serious bleeding from taking warfarin. This is where you bleed suddenly or without a cut or injury, or bleeding will not stop. This can be dangerous and needs urgent medical attention.

An urgent blood test to check your international normalised ratio (INR) should be done when you get treatment for serious bleeding.

Urgent seek medical attention if you have:

• any bleeding that's not heavy but will not stop, or stops then starts again
• pink, red or brown pee, or black poo
• bruises for no reason, they're larger than you'd expect or they keep growing in size
• sudden, severe back pain
• increased bleeding from your vagina during a period or bleeding between periods
• bleeding from your vagina after the menopause

Immediate action required - go to the emergency department at the hospital now if:  

• you have a nosebleed you cannot stop and that last longer than 10 minutes
• there's blood in your vomit or you're coughing up blood

These are symptoms of serious bleeding. If you have any serious bleeding, stop taking warfarin.

Bleeding in the brain

Very rarely, warfarin can lead to bleeding in the brain.

Immediate action required - call an ambulance now if you get any of these symptoms:

• a sudden and severe headache
• a seizure or fit
• sudden loss of vision or blurred vision
• numbness or tingling in your arms or legs
• slurred speech
• cannot be woken up (lose consciousness)
• difficulty breathing, breathing faster than usual, or chest pain
• any heavy bleeding where blood is spraying, pouring or enough to make a puddle
• you may also feel tired, weak or sick

Interactions

Taking warfarin with other medicines and herbal supplements

Cautions with other medicines

Many medicines and supplements can affect warfarin. This can make you more likely to bleed.

You might need a blood test to check the other medicine is not affecting how your blood clots.

If you take warfarin, do not take any new medicines without first checking with a doctor or pharmacist.

Some of the medicines that can affect warfarin include:

• medicines for heart problems, such as amiodarone, quinidine or propafenone
• non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or aspirin
• tramadol, a strong painkiller
• cholesterol-lowering medicines, such as bezafibrate, gemfibrozil, clofibrate or cholestyramine
• antibiotics, such as erythromycin, co-trimoxazole or norfloxacin
• miconazole gel for fungal infections like thrush

Taking warfarin with everyday painkillers

It's safe to take paracetamol while you're on warfarin. But take the lowest dose that controls your pain. Taking more than four, 500mg tablets over 24 hours for longer than a few days may make your blood clot more slowly. This puts you at risk of bleeding.

If you're still in pain after taking paracetamol for 3 or 4 days, speak to your pharmacist or doctor.

Do not take aspirin or ibuprofen while you're taking warfarin unless a doctor has said it's OK. They increase the chance of bleeding.

Mixing warfarin with herbal remedies and supplements

Do not take St John's wort, the herbal remedy for depression, while you're taking warfarin. It can increase your risk of side effects.

Tell your doctor if you're taking vitamin K supplements before you start taking warfarin. Do not start taking vitamin K supplements while you are taking warfarin without checking with your doctor first.

There's not enough information to say that other herbal remedies and supplements are safe to take with warfarin. They're not tested in the same way as pharmacy and prescription medicines.

You must tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.