If you or anyone you know takes warfarin, you may feel that you are being treated like a rat, but not so! Warfarin reduces blood clotting and it also prevents thromboembolism or blood clots. As well, it reduces the risk for conditions such as strokes caused by atrial fibrillation.
It does the same, but is lethal, for pests including rats and mice.
Ideally you want your blood to flow through your circulatory system. When a blood clot forms, it may “plug” the vessel, resulting in thrombosis, for example deep vein thrombosis or DVT. These clots can occur after joint replacement surgery, if you are bedridden and immobile, or even after a long air-plane flight. If the blood clot dislodges from its originating location, it can travel through the circulation “plugging” other vessels in the lungs, heart or brain. This is known as an embolism and may cause emergencies such as heart attacks or strokes.
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Blood clotting involves a series of reactions within your body, and much like a domino effect, one reaction or step causes another. Heparin and warfarin were until recently the two most commonly used anticoagulants. Both interrupt steps in the coagulation process, much like removing a domino in the cascade of steps that leads to a clot.
Heparin is available only as an injectable drug and has a short duration of action. It is ideal for hospital use where its dose can be monitored and dose changes can be made quickly. Warfarin, available as oral tablets, is longer acting, and thus it is suitable for your use at home.
Monitoring is essential with both heparin and warfarin because you don’t want your blood either too thin or with too much of a tendency to clot. With warfarin, regular blood tests are needed and your dose is adjusted depending on the international normalizing ratio or INR result.
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Too much of an anticoagulant can cause bruising and bleeding, and the antidote, vitamin K, may be needed. Warfarin is associated with a long list of potential drug and food interactions, and its effect can be impacted by drugs that can cause bleeding on their own, for example the non-steroidal anti-inflammatory pain relievers, as well as by other medications that interfere with warfarin’s metabolism in the liver and foods that have a high vitamin K content. If you take warfarin, be really aware of what other drugs and foods you can and cannot take.
To prevent clotting after joint replacement, heparin used to be used for several days to weeks after surgery until you were mobile enough so that the risk for clotting had decreased. Heparin required several injections each day, and this led to researchers developing low molecular weight heparin formulations such as enoxaparin and dalteparin. Although these still need to be injected, they only need one injection each day. For the 60,000 Canadians having joint replacement surgery each year, the once daily injection has certainly made recovery easier.
Atrial fibrillation is a heartbeat irregularity that reduces the ability of the heart to pump efficiently. This in turn allows “pooling” of blood and leads to an increased risk of clot formation. This type of arrhythmia is more common than you might think, affecting over 350,000 Canadians, including eight per cent of people over 80 years of age.
Symptoms can be mild, for example palpitations, fainting or chest pain, and they may be attributed to other causes. Increased age, diabetes, high blood pressure, other heart diseases, and even increased alcohol consumption are risk factors. Along with drugs to modify the heartbeat, warfarin is given to prevent clots and stroke. Lifelong treatment is needed along with lifelong blood tests to ensure the warfarin dose is correct.
Recently new blood thinners have been developed that, once the correct dose has been determined, do not need ongoing blood tests, for example rivaroxaban, dabigatran and apixaban. Taken orally, these drugs are effective and convenient, especially for conditions such as atrial fibrillation, but you still need to watch for bruising. And, even as you are reading this, researchers are looking for more effective and safer anticoagulants!
Marie Berry is a lawyer/pharmacist interested in health and education.
