Hi Colm, we have a young man who recently started on warfarin and appears to be very sensitive to it. He is an extremely fit and active man and we wanted to ask can a high level of exercise have an impact on warfarin. We haven't managed to get him within target, any alterations to warfarin caused his INR to rocket or plummet. He is definitely complaint with medications.

Dear Patricia,
The first thing to say is that I am not an expert on warfarin pharmacokinetics.
Increasing metabolic rate would probably increase the metabolism of warfarin hence a higher dose required.
Some patients do tend to be more sensitive to warfarin, especially those that have unusual conditions like antiphospholipid syndrome.

It it is appropriate , changing to a NOAC may be simplier for him, or self testing with an INR machine.
Regards
Colm Rafferty