I was on 50mgx2 lopressor before and now I am in the process of stopping it. I don't notice significant changes in INR. Anyway, if you are not changing your lopressor dosage, it doesn't matter even if there is some interactions.
However, I did develop some problem with my lipid levels. I had (seemingly progressing) low HDL, somewhat-instable-but-not-too-high LDL but very high tryglyceride. Blood sugar was fine. I did some research and also talked to my cardiologist. The suspect is the beta-blocker, lopressor. The beta-blockers, in general, do have the potential to cause the problem I was having and may even lead to diabetes. That's the reason why I am trying to stop it.
Now it's the first week of me totally without lopressor. My blood pressure is raised to about 125/80 from 110/70 and heart rate to 75 from 60. I am waiting for another 2 weeks or so to have my lipid panel done to see if lopressor was the cause. I hope the result will turn out good. On the other hand, I also hope my bp and hr can be lowered a little bit when the after effect of lopressor is totally gone (or maybe it was gone already?). Otherwise, my cardiologist already gave me prescriptions for Corag, which, according to some studies I found online, has less tendency to cause the lipid problem I had.
Not sure if I am the only one who is having this problem. Hope this information is useful.