My range is also 2.5-3.5 on 5mg warfarin for the last several years. I started 81mg aspirin daily a couple years ago with no effect on INR. I was on Coumadin while it was still patent protected and for several years after it was off patent because doctors were scared to prescribe the generic warfarin. I have been on generic warfarin for the past 10-15 years with no effect on INR. I have found that changing brands of warfarin (mfg. tolerances and/or inactive ingredients) can affect my INR......so I am careful to stay with one brand "Taro".
PS: If I miss a dose my INR will also drop like a rock.......that's why I keep pills in a seven day pill box.
I have not seen your entire story, but I am 2015/JUNE with a brand new SAINT JUDE MITRAL VALVE, some have told me, baby aspirin perhaps for life. before this surgery, I had been on regular adult aspirin for many years, i am currently taking none, my INR is suppose to be 2.5-3.5 and is becoming more difficult to maintain as of lately, the VA has had me coming in every 7 days for awhile now, over a month or so. I am going to try and get a machine to self test. the last two tests it was 2.2, so i am now..hmmm steady, ya right I should be so lucky, for the longest I have been on 4mg per day, now they just adjusted it to, 4mg per day, FRIDAY 4.5mg. Mine also sinks, or at least seems to on doses missed, what I do now, is if i catch it fast enough, I will take my missed dose as early the next day then take that days dose a tad later then the time i normally take it, as in...late that night, then back to normal dose that next day, i find this works well. And when they tell you it takes at least 5-7 for Warfarin to kick in, i think that time is a bit less then that, well seems to me anyway. more like 2-3 days to kick in, or less. [what i dont understand is, the first 2.2 INR i had recently, they took me off the shots, then when i tested 2.2INR again, the VA calls me back and tells me, that they had a "chat" and come to the conclusion that i needed to go back onto the shots, uugghhhh, I am not taking them. they even sent me overnight mail, those extra SHOTS even though I already had them from not using them. [[[DOES ANYONE HERE self test, please give me all the data, machine you are using, and the details about using it, cost, and all. I think the insurance covers but i am not sure, am trying to find out now.]]]
Well i do have some very good news, Fla. is a MEDICAL WEED state now, and I came off from using a bit of TRAMADOL [dont use it at all now], + some others i dont remember the name right now, and am using WEED OILS just before sleep at night.