New Blood Thinners

Nov 12, 2013

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

I cant put those books away, they dont go anywhere. There is no room on my shelf! If I put those books on my shelf, all my books will fall down and I wont have any books anymore! My son Eric hasnt studied conical sections in math. Those arent usually taught to eight year olds. They dont go over literary devices in Grade 3 either. However, Eric has mastered hyperbole. He can exaggerate to make his point with the best of them.


I am not saying the claims about some of the new blood thinners on the market are exaggerated, but the big pharma companies are pushing them hard. These three medications are designed to prevent strokes due to atrial fibrillation in patients without artificial heart valves. You've probably seen some of their commercials on American TV. The three new ones are Pradaxa (dabigatran), Xarelto (rivaroxaban) and Eliquis (apixaban). Over the next couple of years they will be joined by edoxaban and betrixaban.


What is atrial fibrillation or a.fib? It is when the top two chambers in the heart, the atria, beat in an irregular fashion that doesn't move blood nice and smoothly down into the bottom of the heart, the ventricles. If blood doesn't flow smoothly, it can clot. A clot in the left atrium would go down into the left ventricle and then could shoot up into the brain. If this clot got stuck into a main artery in the brain, that is a stroke. The part of the brain downstream from the clot dies. And as Dr. Hrabarchuk says, strokes secondary to a.fib. are often devastating and large. They effect large parts of the brain and can even lead to death. Strokes secondary to a.fib. are not something you want.


We have been successfully preventing strokes from a.fib. for years with a drug called warfarin. It works well. The experts say that for every 32 people with a.fib. that you give warfarin to for 1 year to you will prevent 1 stroke. That is an impressive number. Warfarin can also be used to treat blood clots in the legs and lungs, prevent another heart attack, stroke or death after a heart attack, and preventing stroke if you have a mechanical heart valve. Warfarin can also be used if you have poor kidney function. We have blood test called the INR (international normalized ratio) available to see if your warfarin is working and we have an antidote (Vitamin K) to reverse the effects of warfarin if you get too much. Warfarin has its problems too. Warfarin interacts with many, many drugs and foods. So if you are on warfarin, you will have to get your INR checked at least once a month. Warfarin can make you bleed too much and cause things like bleeding in your guts. At the moment though, warfarin's big advantage is that it is cheap! For less than $30 per month warfarin will protect you from a stroke. Compare that to about $170 per month for apixaban.


Dabigatran or Praxada was the first new blood thinner in Canada. It is taken twice a day and it will prevent 5 more strokes per 1000 patients per year compared to warfarin. It has about the same bleeding risk as warfarin. Although dabigatran was the first drug to prevent strokes due to a.fib. better than warfarin, the improvement is very small. For practical purposes it is probably safe to say they are the same. Unless you were running a clinical trial with thousands of patients, you probably wouldn't be able to tell the difference between dabigatran and warfarin. Dabigatran doesn't have an antidote and if it is used in patients with very poor kidney function it may last way too long and may cause patients to bleed for a long time.


Rivaroxaban or Xarelto isn't better than warfarin at preventing strokes due to a.fib. Even with thousands of people in a clinical trial you wouldn't see any difference between rivaroxaban and warfarin. It has similar bleeding risks to warfarin. Again it shouldn't be used in patients with poor kidney function. Again it doesn't have an antidote. It's only real advantage is that it is the only one of the three new blood thinners that is a once a day pill.


Apixaban or Eliquis is the newest kid on the block. It is taken twice a day. It prevents about 3 more strokes per 1000 patients per year than warfarin in patients with a.fib. It also causes 10 fewer bleeds per 1000 patients per year than warfarin. Those are both good, but not really that much different that warfarin. There was also a strange study that compared apixaban to ASA to prevent stroke due to a.fib. Apixaban was better than ASA at preventing strokes and caused bleeds at about the same rate as ASA. The strange part is that ASA is not the first choice to protect against stroke secondary to a.fib. Warfarin is much better at protecting against stroke secondary to a.fib. So we would only use ASA if there was some reason we couldn't use warfarin in a patient. Apixaban can be used in patients with slightly worse kidney function than dabigatran or rivaroxaban. However, anyone on dialysis would still probably need warfarin because their kidney function would probably be too poor to use any of the new blood thinners. And again there is no antidote.


All three of these drugs are being promoted as good alternatives to warfarin. However, they are much more expensive and at best they are a little bit better than warfarin. These new blood thinners promote that no INR blood tests are needed. However, this just means we have no blood test available to see if they are thinning the blood the right amount or not. There can be many reasons why a patient has their INR levels bounce around. One reason is the patient doesn't do a good job of remembering to take their pills. Warfarin lasts in the body for about 3 days. If a patient forgets a warfarin pill once in a while, it doesn't really matter. However with the much shorter length of action of the new blood thinners, what will happen when a person misses a day of the new medication? It is possible they will now be a risk of a stroke. So switching people who arent compliant with their warfarin to one of the new blood thinners might be problematic.


I am not saying the new blood thinners are bad. In fact they are very good and it is great to have new stroke prevention tools in the a.fib. toolbox. But they are expensive, only marginally better than warfarin at preventing stroke and dont have an antidote. Just like I didnt believe that Eric putting his books away would magically make all his books disappear, I dont believe that everyone on warfarin should automatically be switched to a new blood thinner.


The information in this article is intended as a helpful guide only. It is not intended to be used as a substitute for professional advice. If you have any questions about your medications and what is right for you see your doctor, pharmacist or other health care professional.


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