Two inquests this week blamed warfarin for causing brain haemorrhages in elderly women. Dr Muiris Houston, Medical Correspondent, examines its role in treatment
Separate inquests this week were told that the anti-clotting drug warfarin was to blame for the deaths of two elderly women. Their deaths from brain haemorrhage emphasise the particular precautions that must be taken with the medication.
Warfarin is the most commonly used oral anticoagulant. It blocks the effect of vitamin K in the liver, thereby interfering with the formation of vitamin K-dependent clotting factors. Warfarin thins out the blood and makes it difficult for blood to "clump".
Unlike most other medications, the maintenance dose of which remain constant, the dose of warfarin regularly changes depending on the results of a blood test called the prothrombin time. This test, which measures the rate of clotting, is an essential part of warfarin treatment. It must be constantly monitored so that the level of the drug in the body produces the correct amount of blood thinning. If the level rises above a certain threshold, there is a high risk of internal bleeding, including brain haemorrhage. Should the level drop below a certain point, the therapeutic effect of the drug is lost. The level of active warfarin in the system is sensitive to changes, such as the development of an acute illness. A deterioration in liver or kidney function or the development of heart failure will also significantly alter the activity of warfarin in the body. And warfarin interacts with a large number of other medications, including certain painkillers and antibiotics.
Patients taking warfarin should seek medical help if they develop bleeding in the nose or gums, discoloured urine or prolonged bleeding from cuts and bruises. The appearance of red or black bowel motions is another warning sign.
The main indications for using warfarin are in patients who have had a clot in the leg, a clot in the lung or those with a rhythm disturbance of the heart called atrial fibrillation. People with artificial heart valves must also take anti-coagulants because of the risk of a clot forming on the valve. Because these are life-threatening conditions, the use of warfarin in their treatment is considered appropriate.