Martin: Consistent dosing is a good thing. Jumping between 3.0 and 4.5 on various days will give you a different INR reading, depending on which day's dose is having the demonstrated effect. (I know this - I did quite a bit of daily testing, and, for myself, at least, there WAS a daily fluctuation that was probably due, in part, to different daily doses).
From what you've said, your weekly dose is 27 mg (3*3=9, plus 4.5*4=18). It would probably make more sense to take 4 mg for six days and 3 mg for the seventh day - to reach the same weekly dose and avoid fluctuations in your INR. If your INR is on the low side of your range, it may make sense to try 4 mg a day and see how this more consistent dosing effects your INR. (Warfarin is available in 4 mg tablets, so this would be pretty easy)
