Thanks for your question.
Achieving a stabilized INR while on warfarin
can be quite challenging sometimes. Several antibiotics (penicillins and cephalosporins) and even certain vegetables have been known to interfere with its metabolism
and consequently its actions. I would suggest that you interact with your physician, with a view to re-evaluate all your medications (and possibly, meals), to determine which, if any, interact with warfarin.
Having said that, I would also mention that you keep to a fixed time of warfarin intake, preferably well after the last meal of the day (i.e. just before bed). Avoid, as much as possible, any food or medication that may interfere with it. All PT tests should be done in certified labs, and all values converted to INR. I hope these measures will help.