Dabigitran and Atrial Fibrillation

Nov 15, 2010

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

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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.

Do you remember when plasma TVs first came out? They were very cool and flat and all the rage. And they cost about $10,000 at first. So the question was even though they could do things a regular TV couldnt, were they worth the money? Were they worth the money especially when a traditional TV cost only a few hundred dollars? Can new drugs be like a plasma TV?

Dabigatran is a new blood thinner. It is being promoted as being able to prevent strokes in patients with atrial fibrillation. Atrial fibrillation is a type of irregular heart beat or arrhythmia. Your heart has four chambers. The two atria on the top of the heart are small chambers which accept blood either from the whole body or the lungs. They pass this blood off onto the bigger chambers of the heart, the ventricles. The right ventricle squishes blood to the lungs to get filled up with oxygen again. The left ventricle is very big and strong and squishes blood to the whole rest of the body.

If your ventricles start quivering and not moving blood around properly, that is very bad. It is called ventricular fibrillation and if it isnt fixed quickly by something like a shock from a defibrillator, you will die. Atrial fibrillation, or quivering and not squeezing properly by the small chambers on the top of the heart is not fatal. In fact, you may not even notice you have atrial fibrillation. The danger with atrial fibrillation is the blood clots.

Your blood is designed to clot, which is good. If your blood didnt clot, you would bleed to death with every paper cut. Several things can set off the clotting cascade. If blood comes in contact with the rough edges of a wound, it will cut. If blood comes in contact with air, it will clot. If your blood stops moving in a nice smooth, laminar way, it will clot. This last one is the problem in atrial fibrillation. When the atria start quivering and not beating smoothly, the blood flow through them gets turbulent. That turbulent flow can lead to blood clots. These blood clots will then travel into the ventricles. The clot we worry about the most would go into the left ventricle and be shot out up into the brain. If that clot got stuck in a small blood vessel in the brain, it could stop all the blood flow past it. That section of the brain would die due to lack of blood and oxygen. That is a stroke.

So now it should make sense why we treat atrial fibrillation with blood thinners. If we make the blood less able to clot, then even if there is turbulent blood flow in the atria, we shouldnt get blood clots being shot up into the brain to cause a stroke.

So which blood thinner should you use? At the moment warfarin is usually the blood thinner of choice. ASA or aspirin may be used if the patients stroke risk is very low or if they are intolerant to warfarin. Warfarin works by interfering with how Vitamin K in used in the clotting cascade. The good thing about warfarin is there is a blood test called an INR we can do to see exactly how thin we are making the blood. And warfarin is quite inexpensive. The bad thing about warfarin is it interacts with many foods and medications. Some patients have to have the INR blood test done every week or more to see how thin their blood is.

Dabigatran is an oral reversible direct thrombin inhibitor that can be given in fixed daily doses independent of age or bodyweight. That means that we dont have to do blood work to see what dose of dabigatran we need. It also shouldnt have all the drug and food interactions that warfarin does, so it should be simpler to take. There was a study published by Diener et al in the November 2010 Lancet Neurology that looked at dabigatran versus warfarin in preventing strokes. It was a nice big study with over 18,000 people either put on dabigatran or warfarin. Interestingly, the study was not double blinded. The researchers knew which patient was on which drug. The results showed that dabigatran was probably as good as warfarin at preventing stroke. The dabigatran might be worse than warfarin at causing bleeds in the stomach. The dabigatran is probably causes fewer other bleeds than warfarin.

It is good we have another tool to combat strokes in people with atrial fibrillation. The biggest problem with dabigatran is its price. Whereas a month of warfarin would cost about $25, a month of dabigatran would cost about $125. That is $100 more per month. And because it is new, pharmacare will not pay for it. So like the original plasma TVs, is it worth the price? For some people it will be. But for most people with atrial fibrillation, warfarin will still be the affordable choice.

As always if you have any questions or concerns about these or other products, ask your pharmacist.

 


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