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Warfarin Sensitivity Genotyping

Orthopedic Algorithm10

Slide 22

August 2008

There are various algorithms that are now being published on how to dose warfarin. One that was recently described is for an orthopedic algorithm and that is a dose revision algorithm in that on day three the INR is reevaluated and the dosing revised based on changes in the INR.

So if on day three, the INR after the third dose exceeds the 0.25 unit rise, then you would reduce the dose. You would reduce the dose for the CYP2C9 genotype by varying percentages 17% for a *2 allele, 37% for a *3 allele, you have to readjust based upon the absolute dose of warfarin given, the estimated blood loss that occurred because plasma proteins may not be replaced if you are using packed red cells. Smoking increases the requirement for warfarin because that stimulates warfarin metabolism, and if you have a VKORC1 1639A allele you have an 11% reduction per each allele. If you take all of these together you can explain roughly 80% of the dosing variability in orthopedic patients.

Orthopedic Algorithm10


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