The Anonymous Widower

Interaction Between Warfarin And Terbinafine

A few weeks ago I was prescribed a course of oral Terbinafine to clear up a fungal infection. It seemed to work well, except that there is still some of the tinea in my toe-nails.

But over the time, I was taking the drug, I have felt that my INR was constantly wanting to slip downwards towards and below two.

Luckily I test my INR daily, and use a simple control algorithm to calculate my Warfarin dose. Normally, it is 4 mg, but if it goes below 2.3, I increase it to 5 mg, and if it goes above 2.8, I reduce it to 3 mg. So the algorithm got me taking a lot of 5 mg doses as opposed to the usual4 mg.

Only since I finished the course of Terbinafine has the INR stabilised around 2.5, which is my target value.

I didn’t at first see any link until everything settled after the course finished.  But I decided today to type “Warfarin Terbinafine interaction” into Google. I found this paper from the BMJ entitled Drug points: Serious interaction between warfarin and oral terbinafine.

I think this minor incident shows the value of regular INR testing! Because I was testing daily, as the INR started to drop, my algorithm told me to increase the dose to 5 mg.  In fact my average dose has gone up from 4 to 4.5 mg. in the period that I was taking the Terbinafine.

So there was no harm done at all!

April 25, 2014 - Posted by | Health | , , ,

2 Comments »

  1. Sadly though, most people don’t test daily, and wouldn’t have known. I do regular blood tests, but most diabetics don’t unless they are on insulin (which I am not). I would make it a legal requirement that every diabetic did a blood test before they got behind the wheel of a car.

    Comment by nosnikrapzil | April 26, 2014 | Reply

  2. […] is very much a repeat of my experiences of taking Terbinafine, which I wrote about Interaction Between Warfarin And Terbinafine. Although that drug dropped the […]

    Pingback by Warfarin And Lansoprazole « The Anonymous Widower | December 29, 2015 | Reply


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