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Warfarin Sensitivity Genotyping

Patient Case: Rapidly Increasing INR

Slide 25

August 2008

Here is an example of a case in which there was a rapidly increasing INR which shows the factors that have to be considered in dosing for a patient. In this particular case the INR climbed to over 13 within a week.

The patient was dosed correctly for age, gender and body weight however there were factors that increased the INR beyond what would be calculated based upon the non-genetic factors. When tested by genotyping, the patient was found to have polymorphisms in both CYP2C9 and the VKORC1 gene and so to start with they should have had a 48% dose reduction as indicated in the algorithm table of dosing for genotypes. But in addition there was co-morbidity because the patient was receiving chemotherapy which can alter coagulation.

In this case a dose decrease would have been warranted based upon the co-morbidity. In addition, the patient was receiving a co medication which is quite inhibitory of CYP2C9 that is Fluconazole and so a dose decrease should have been given as well for that or the patient should have been switched to a different antibiotic.

So utilizing genotyping, the drug interactions and the co-morbidity information the patient would have received initially only 5-10% of the initial dose as estimated based upon non genetic factors.

Rapidly Increasing INR


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