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Indications

Warfarin Sodium is an anticoagulant, often called a blood thinner. It is used to treat and prevent blood clots in the veins of the legs (deep vein thrombosis) and lungs (pulmonary embolism), and to lower the risk of stroke in people with atrial fibrillation (an irregular heartbeat) or mechanical heart valves. It is also used after some heart attacks and in other conditions with a high risk of clots.

How It Works

Warfarin blocks the action of vitamin K in the liver. Vitamin K is needed to make several clotting factors (proteins that help blood clot). With fewer working clotting factors, blood takes longer to clot, so harmful clots are less likely to form or grow. It takes a few days to reach its full effect.

Dosage and Administration

The dose is different for every person and is adjusted by the doctor according to a blood test called the INR (international normalised ratio). Take exactly as prescribed, once a day at the same time, usually in the evening. Do not change the dose or stop taking it without medical advice. If you miss a dose, take it the same day if you remember; never take a double dose the next day. Keep a record of your doses and INR results.

Interactions

Warfarin interacts with a very large number of medicines, foods and herbal products. Aspirin, Clopidogrel, Ibuprofen, Diclofenac and other painkillers of this type greatly increase bleeding risk; Paracetamol in regular high doses can also raise the INR. Many antibiotics (such as Ciprofloxacin, Metronidazole, Co-trimoxazole, Erythromycin and Clarithromycin), antifungals (Fluconazole, Miconazole), Amiodarone, Omeprazole and some cholesterol medicines can increase its effect. Rifampicin, Carbamazepine, Phenytoin and St John's Wort can reduce its effect. Large changes in foods rich in vitamin K (green leafy vegetables) and alcohol intake also change the INR. Always tell every doctor, dentist and pharmacist that you take Warfarin, and check before starting or stopping any medicine or supplement.

Contraindications

Do not take if you are allergic to Warfarin, if you are pregnant (especially in the first 3 months and near delivery), if you have active bleeding or a high risk of bleeding (such as an active stomach ulcer, recent bleeding in the brain, or recent major surgery on the brain, eye or spine), severe uncontrolled high blood pressure, or severe liver disease.

Side Effects

• Bleeding: nosebleeds, bleeding gums, easy bruising, heavier periods
• Nausea or vomiting
• Hair thinning
• Skin rash
• Rarely, painful skin patches that turn dark (skin necrosis) or purple toes

Get urgent medical help if you have signs of serious bleeding: blood in urine or red or black stools, vomiting blood or material like coffee grounds, coughing up blood, a severe headache, sudden dizziness, weakness or confusion, a nosebleed that does not stop, or a fall or blow to the head.

Pregnancy and Lactation

Warfarin can cause birth defects and bleeding in the unborn baby and must not be used during pregnancy, except in rare cases decided by a specialist (for example some women with mechanical heart valves). Women who can become pregnant should use reliable contraception and tell their doctor at once if they plan to become or become pregnant. Warfarin can usually be taken while breastfeeding, as very little passes into milk.

Precautions and Warnings

Regular INR blood tests are essential. Carry an anticoagulant card or note. Keep your diet and alcohol intake steady. Tell your doctor about any illness with vomiting, diarrhoea or fever, as these can change the INR. Take care to avoid injuries, use a soft toothbrush and an electric razor. Your doctor will plan how to manage Warfarin before any surgery, dental extraction or procedure. Older people and those with liver, kidney or thyroid problems may need closer monitoring.

Overdose

Too much Warfarin can cause serious or life-threatening bleeding. If you take extra tablets, or a child swallows any, seek medical help immediately even if there are no symptoms. Doctors can reverse the effect with vitamin K and other treatments.

Therapeutic Class

Oral anticoagulant, vitamin K antagonist (coumarin type).

Storage

Store below 30°C in a dry place, away from light and out of the reach of children. Keep different tablet strengths clearly separated to avoid mix-ups.