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Warfarin Sensitivity Genotyping

INR Variability in a 74 Year-old Male

Slide 7

August 2008

Now here is an example of the variability in INR in a patient. This is a 74-year-old male and the warfarin was dosed based upon the usual non-genetic factors of weight, height and age. This particular case within the first week, the patient had already exceeded the up limit of 3. By week 2 they had gone to an INR greater than 12, this is quite dangerous.

Between week 2 and 3 something happened as indicated by the arrow. In this particular case the patient experienced a cerebrovascular bleed; they were administered vitamin K to block the effects of warfarin and warfarin was discontinued for a period of time until the INR dropped down to near the therapeutic level.

It was very difficult to stabilize this patient and maintain him within the therapeutic range. This patient was enrolled in a research study and years later it was discovered that they had polymorphism within two genes that are responsible for maintaining the INR within this certain range.

This particular warfarin dose calculated by genetic factors should have been decreased based upon the genotyping done subsequently by 80% to maintain him in the therapeutic range.

INR Variability


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