Clinical effect of CYP2C9*5/*6 genotype on a patient's warfarin dose requirement.

We describe a 38-year-old African-American female treated with warfarin for acute bilateral pulmonary emboli who is a carrier of two rare CYP2C9 variant alleles, *5 and *6, along with VKORC1 -1639GG and CYP4F2 433Val/Val genotypes. Warfarin was dosed according to the hospital's Personalized Medicine Program recommendations of 5-6 mg/day for the first 6 days, and reduced to 2.5 mg/day starting on day 8 and continued for the following 3 weeks. This case sheds further light on the cumulative clinical impact of the CYP2C9 variant alleles, *5 and *6, on warfarin dose requirements and practical considerations for warfarin genotyping in a racially and ethnically diverse population.