I switched from Coumadin to warfarin several years ago with no problem in INR results. However, I have found, over the past few years, that there can be some difference between brands of warfarin that can affect my INR. I now use only one brand and seldom have any INR problems. My pharmacist agreed that it is best to stay with one brand as there are acceptable tolerances between drugmakers. My own experience is that vit K foods have the biggest impact on my INR. I try to have some "greenies" most every day and that helps keep me in my range of 2.5-3.5.
FWIW, there are two warfarin brands in the US that have been around for years....Barr Labs and Taro. I have used both with no problem, but have settled on Barr Lab for consistency. I had a "big box store pharmacy" substitute a little known foreign brand that caused me a great deal of INR problems. Once I stopped using that brand my INR settled down.
can you give some numbers with respect to your range?
Also, Coumadin is warfarin , but I understand there is a generic just named after the compound (which is warfarin)
I have seen people reporting that using the generic brands they have had inconsistency of INR greater than before. However personally I find that in my life there are periods where its a little more inconsistent than other times. I have found that a week of exersize (in Australia that means a week of cycling) almost always pushes my INR down (and thus I need to raise my dose by between 0.25 and 0.5mg a day (and yes I split 1mg tablets into 4).
note the trends and my dose adjustments in the above.
If you're between those extremes (1.9 ~ 3.5) of range but mostly (average) in the middle then you're fine.
Pick a decent brand and stick with it (I use Marevan but then that's just what I happened to be started on)