Warfarin Genetic Variances

Question 1

How do CYP2C9*2 and 3 differ from CYP2C91?

Answer 1

CYP2C9*2 and *3 decrease S-warfarin clearance by 40-70% and 90% respectively

Question 2

What CYP2C9 allele combination occurs in 1/3 of white patients?

Answer 2

2/3

Question 3

How does the -1639A amino acid substitution differ from the -1639G amino acid subsitution?

Answer 3

The A substitution decreases VKOR production therefore increasing warfarin sensitivity while the G substitution does the opposite and increases warfarin resistance

Question 4

Which amino acid substitution combination is most common in Asians?

Answer 4

-1639AA

Question 5

Which amino acid substitution combination is most common in African Americans?

Answer 5

-1639GG

Question 6

What are the three criteria that must be met in order to warrant warfarin genetic testing?

Answer 6

-Patient must be warfarin naive (never had warfarin before)
-Genetic results must be available before the sixth dose
-Patient must be at a high risk of bleeding if the INR is elevated (i.e. patient is on other medications that increase bleed risk)