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Warfarin (Part 1)

Posted Jul 10 2009 10:47pm
This post is specially designed for those taking warfarin (well, this is going to be very text book material).

First, why your doctor prescribed you warfarin?


You need to take warfarin when you have a medical condition which need an anticoagulant to reduce clotting, thrombosis and embolism (abnormal formation and migration of blood clots), which are atrial fibrillation (AF), in the presence of artificial heart valve, deep vein thrombosis (DVT), pulmonary embolism, post myocardial infarction (MI - heart attack), etc.

Now the question comes to: Why need to reduce clotting, thrombosis and embolism?


If a blood clot (thrombus) is formed, it might migrate to a spot where it blocks blood supply to vital organs (embolism). Therefore, as high risk patients (which your doctor will evaluate the risk), you need to take warfarin to prevent the future blood clot from forming in your body.


Of couse, your body also need the formation of blood clots. This is how our body response to protect us from excessing bleeding; for example, when we cut ourselves.

As you need blood clot to protect yourself, and you don't want it to kill yourself, you need a balance. That is why the international normalized ratio (INR) comes in.




INR is the measurement of therapeutic effect of warfarin. Normal value for normal people is in between 0.8 t0 1.2. For high risk patients, the INR will be targetted higher, depends on the condition. It tends to be 2 - 3 in most conditions, but it will be up to 2.5 - 3.5 in patients with mechanical heart valve(s). Optimizing INR is important to ensure the achievement of desired therapeutic effects without risking dangerous side effects such as bleeding.

Targeted INR is obtained through the dosing of warfarin. However, it is a complicated process as it will be interacted with many commonly used medications (I'm sure those who need to take warfarin, need to take many other medications as well), and also with the chemicals present in the foods.

So, your INR might change from time to time, even though you are taking the same dose all along. Therefore, you need to follow up with your doctor and pharmacist, to get INR check from time to time, depends on your appointment. If the INR is maintained, the dose will be maintained. If not, your doctor will decide to change dose or not. At the same time, your pharmacist will assess your compliance, and also other factors that might affect the INR, then only decide change dose or just get rid of the factors that affect the INR.

So, constantly follow-up is important when you are taking warfarin!

(Next post will talk about warfarin administration, precautions and advice on lifestyles)
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