I've been on Coumadin and/or warfarin and/or Jantoven since 1990. I've always had an extremely constant INR over the 25 years. But today, my INR came in at 1.4, which is way below the therapeutic level of 2.0 and way -way below my target of 2.5.

I was struggling quite a bit about why all of a sudden I have such a low INR. When I checked my Jantoven bottle, I found that what I have been taking the last two weeks is outdated - expiration was 11/16/2014. My intent was to use up my "emergency supply" and replace it with some new pills but I did not realize how old this prescription was.

Is it possible that Jantoven's effectiveness goes to near zero after two to three years? And if that's true is it possible that the effectiveness might drop over the year before it expires? Is it possible that the change in Jantoven's effectiveness over time may contribute to the difficulty that many people have controlling their INR?

Thanks for any insight.