Harvard Heart Letter

Ask the doctor: Should I try one of the new blood thinners?

Q. I have atrial fibrillation and have been taking warfarin to prevent blood clots for 10 years. It has not given me any problems. However, I do hate going to my doctor's office to get my INR blood test every month. I'm wondering whether I should switch to one of the newer blood thinners that don't require blood testing.

A. If you have been successfully taking warfarin for this long, and do not have problems with wide, unpredictable variations in your INR levels, I would recommend that you stay on warfarin. The newer drugs, which include dabigatran (Pradaxa) and rivaroxaban (Xarelto), are wonderful innovations, but they have undergone less testing than warfarin.

Although their risk of causing unwanted bleeding is somewhat less than that of warfarin, if most of your INRs have fallen within the target range, it's not clear whether your risk of bleeding will be lower with a new agent. Also, with these new agents, there is no known way to tell whether you are getting too much or too little of the drug. In addition, dabigatran needs to be taken twice a day. So, I would not rush to these new drugs just for convenience's sake. Since you are doing so well on warfarin, I would wait a bit and see what additional information becomes available.

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