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Blood thinners – warfarin and heparin

Warfarin and heparin are anticoagulant medications, often referred to as blood thinners. These help prevent clots from forming in the blood. Anticoagulants are used to treat some types of heart disease and to prevent dangerous blood clots. These include:

  • Deep vein thrombosis or DVT - blood clots in the leg veins
  • Pulmonary embolism - blood clot in the lungs
  • Atrial fibrillation - irregular heart rate

Warfarin

Warfarin is the most commonly prescribed anticoagulant. It is taken as a tablet and works by slowing production of vitamin K and in turn, the protein prothrombin, which is important for blood clotting.

The dose of warfarin needs regular monitoring at a GP's surgery, clinic, hospital or pharmacist to make sure it is correct. This will take place less often once the dose stablilises. For some people it may be possible for them to monitor their warfarin levels at home.

Warfarin dose

This is done with the international normalisation ratio (INR) blood test.

Too high an INR level means blood clots won't form quickly enough, which increases the risk of bleeding and bruising.

Too low an INR means the dose is too low and blood clots could still develop.

The dose is adjusted by taking differently marked tablets to add up to the current prescription amount. Take the dose as advised by the doctor. Warfarin is usually taken once a day, at the same time, usually in the evening.

Seek medical advice if a dose is missed or an extra dose taken by mistake.

Warfarin warnings

Warfarin can interact with other medicines, so make sure your doctor or pharmacist know what else you take, including supplements and over-the-counter medicines.

Aspirin or ibuprofen should not be taken with warfarin.

Binge drinking can affect the way warfarin works. So can cranberry juice and food rich in vitamin K, such as spinach and broccoli.

A person taking warfarin will be advised to take extra care to avoid injuries from daily activities from shaving to playing sport as they are more prone to bleeding.

Heparin

Heparin is a natural substance in the body, but can also be used to inhibit the blood clotting process. Unlike warfarin tablets, heparin is given as an injection or IV drip.

Heparin may interact with other medicines, supplements and alcohol.

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WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on October 26, 2012

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