Holidays and Timezone Changes

I always test and dose at 9pm every day.  Going on holiday or business trips has enough capacity to disrupt warfarin without forgetting a dose, so I decided to timezone adjust my dose to keep it at 9pm.

On this occasion I'm going to Bangkok, and i'm taking something around 8mg daily.  Bangkok is 7 hours ahead of home, so I worked out my dose assuming 8mg is over 24 hours like this:

8/24 = 0.333  x 17 = 5.66.  So I need a 5.6 dose instead of 8.

Then when I return I do the opposite:

8/24 = 0.333  x 31 = 10.3.  So I need a 10.3 dose instead of 8.

Here's an example, results and doses:

INR High for no reason

Things have been pretty stable for a while now.  Just the odd subtle dose change to handle a trending high or low.

Suddenly, for no reason, a test came back at 3.8.  And I mean no reason.  I felt fine, diet was normal, exercise was normal.

I adjusted the dose to cope with it a little, ate lots of green food, and problem went away.  This was the first in a number of lessons that warfarin is not a stable drug. It can just change on a whim.  If I hadn't been self testing - presumably it would have just gone high... perhaps come down on its own after a while.  Hopefully i would have avoided any major problems, but who knows.  One bit of bad luck, as sods law often dishes out, and I would have had a big problem.