What is it?
Warfarin is a blood thinning tablet that reduces the natural tendency of blood to form
clots. It acts on the liver to reduce the production of some clotting factors which rely on
Vitamin K. This means that your diet should have a not too excessive and steady intake
of foods that include Vitamin K (green leafy vegetables).
What is it used for?
There are many uses for Warfarin. It is used in patients with atrial fibrillation where the
irregular rhythm reduces emptying of the collecting chambers of the heart and increases
the chance of strokes.
It is used in patients with clots in the legs (DVT) or lungs (pulmonary emboli). It can be
used after heart attacks where there is a concern of clots developing in the heart chamber.
Warfarin is also used in patients with artificial heart valves and for a short period after
heart vale repair surgery.
What are the side effects?
The main risks of Warfarin occur if the blood becomes too thin. These include an increased
bleeding tendency and bruising. Warfarin can rarely cause a rash or hair loss.
How do you monitor treatment?
Warfarin is monitored by taking blood from you and measuring how long it takes to form
a clot. A ratio is calculated comparing your blood with blood from non-treated patients.
A normal result would be a ratio of 1.0. On Warfarin there is a higher ratio usually between
1.5 and 3.5. The ratio is called the INR and is the same in every country of the
The degree of thinning required varies with the condition that is being treated. In atrial
fibrillation the ratio is usually between 2.0 and 2.5. Artificial heart valves require a ratio
between 2.5 and 3.0. The treatment of blood clots requires levels between 3.0 and 3.5.
Initially you will require frequent blood tests while establishing the correct dose. The
laboratory service will take your blood and call you later that day with the doses for the
next few days and an appointment for your next blood test. After stabilising your dose
the tests become less frequent and eventually are once every four to six weeks.
It is vitally important to have regular blood tests to ensure the INR levels remain
within the prescribed range both for efficacy and safety.