A couple of weeks ago, my dentist found a small lump in my mouth,so he advised getting it removed and tested to see that it was nothing serious. The procedure was booked to take place on Thursday, the 30th of July and he advised me to make sure my INR was lower than 2.4 and not to take any Warfarin on the day before. Obviously, he didn’t want me to bleed too much, especially as the position of the lump made stitching impossible.
My INR had been 2.6, 2.5 and 2.6 on the Sunday, Monday and Tuesday, taking my normal dose of 4 mg., which as I take it most days, is unsurprisingly my average dose.
On the Tuesday, to lower te INR slightly, I cut my dose to just 1 mg., with the consequence by Wednesday morning the INR had dropped to 2.3. As the doctor had said no Warfarin on the Wednesday, my Control Engineering training said that could drop the INR below 2. So I just took 1 and the INR was 2.1 on the day f the operation.
After the operation, as I wasn’t bleeding I took 3 mg of Warfarin, but by the Friday morning my INR had dropped to 1.6, so that evening I took 6 mg. On the Saturday morning, the INR had gone up a bit to 1.7, so to nudge it towards the desired value of 2.5, I took six that day.
In the week of the operation despite changing the dose to control my INR, I sactually averaged 3.8 mg. over the week.
Since then I’ve taken my normal 4 mg. and my INR has been fairly steady around 2.4.
I think this exercise shows the value of self-testing your INR. Admittedly, I was employing my Control Engineering training and experience to give the doctor what he wanted and keep my INR at a reasonably safe level, but the ability to self-test regularly around an operation must make things better for everybody concerned.
The doctor told me afterwards that I hadn’t bled too much, but then when I’m cut by a professional as opposed to torn in a fall say, I don’t seem to bleed much!
In the end, the lump had been removed and I heard today, that it was totally benign.
I take quiet a few medicinal drugs. Every day, I test my INR and then put the drugs for the next twenty-four hours in an old black 35 mm. film canister, which fits neatly into the bag I generally carry or a pocket of my coat.
When I go away for a few days, I put the required drugs plus a few for luck, in a white film container, which I then transfer to the black one every morning.
Look at these two pictures of two strips of drugs.
One is Spirolactone and the other is 1 mg. Warfarin. When I went to Glasgow because I was in a hurry, I took two Warfarin instead of two Spirolactone. It didn’t matter in this case, but for others similar mistakes could be more serious. A contributory factor in this mistake, was that Boots have started to give me a differently packaged brand of the Warfarin.
The top side of the drug packaging should be distinctive. I think too, that the old brand of Warfarin had the writing on the back in the same colour as the drug. i.e. brown in this case. The new one is just an anonymous black.
This graph shows my INR a period between the 20th of May and the 25th of June.
I should say that I have a degree in Control Engineering from Liverpool University.
My aim here is to keep my INR between two and three, with a target value of 2.5.
Since starting to self test, I normally take around 4 mg. a day of Warfarin, but I have found that five is a better dose for when I’m taking Terbinafine, which has been prescribed by my GP for a fungal infection. The drug is well-known to affect the action of the Warfarin.
So now I take 5 mg. unless the INR is 2.8 or more. In which case I reduce the dose from five to four. On the other hand, if the level is 2.2 or below, I increase it to six.
The average INR value for the period shown was 2.6 with a standard variation of 0.2.
The peak at the beginning of June may have been caused by a B12 injection or hot weather. Both of which seem to raise my INR.
You will notice that the INR went up around the beginning of June. I can’t be sure, as I don’t have the dates, but this may have been caused by having a B12 injection.
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!
I’ve now been testing my INR using my Coaguchek device for five months now.
I’ve missed very few days.
Nothing worries me about the results, but suppose you were testing every two weeks or so, you might start to get the impression your INR results were not what they should be.
I’ve now got enough data to start doing some serious analysis.
This morning, I cut my hand accidentally, as I walked the Regent’s Canal. How I don’t know, but despite timely repairs by the nurse at my surgery nearby, the wound refused to stop bleeding and I had to go to A & E at University College Hospital.
The nurse at UCLH, who bandaged my hand, put the bleeding down to the interaction between Warfarin and the other drugs I am taking.
The strange thing is that I can now type easier and get the Shift and Control keys right.
As September is now finished, I can show a graph of my daily INR tests for September 2013.
The average INR for the month was 2.4 with a standard deviation of 0.2. This is well within the range of 2 to 3 and just below the target of 2.5.
Note the drop in INR starting at the 19th. This was when the weather started to get colder and fresher. The lowest value of 1.9 on the 27th was after a particularly cold night.
Compare this graph with previous results for August 2013.
I get on well with my Coaguchek, but I did have a failure in Sweden.
The batteries chose to run out and I then had to reset the device.
Unfortunately, it is not an easy process to do without the manual, which I deliberately had not taken.
An ideal device would have a quick setup, where it took defaults for everything. After all, you always write down all your results and don’t rely on things like the date set into the device.
Everything should be simple and intuitive. It isn’t and the manual is needed too often. It also just gives you error numbers, rather than a proper error message.
The outcome was that I missed one of daily tests. Not important for me, as I just took the average Warfarin dose of 4 mg.
As August is now finished, I can show a graph of my daily INR tests for August 2013.
The average INR for the month was 2.5 with a standard deviation of 0.3. This is well within the range of 2 to 3 and the average was spot-on the target of 2.5.
Having once been told by an eminent cardiologist, that if I got the Warfarin level right, I probably wouldn’t have another stroke, I try to make sure I get it right.
What is interesting is that my average Warfarin dose for month is exactly 4 mg. a day.
The more I look at these results, the more I believe that daily self-testing is the best way to control INR.
To illustrate the changes you get in INR, I’ve made a graph of my last fourteen readings.
As you can see the level goes up and down, but stays within the limits of 2 and 3, with an average of about 2.5.