Results No difference in primary endpoint of percent OOR INRs (Figure) In subgroup analysis, percent OOR INRs in genotype-guided warfarin group vs. standard group in patients with either wild type or multiple variants (29.3% vs. 39.1%, p = 0.03) dose changes/pt in genotype-guided group (Figure) Conclusions Among patients requiring oral anticoagulation, use of genotype-guided warfarin dosing regimen was not associated with difference in percentage of OOR INRs compared with standard warfarin dosing However, reduction in OOR INRs was seen with genotype-guided warfarin dosing in patients with either wild type or multiple variants Warfarin has wide interpatient variability, which can result in excessive dosing within individuals when only guided by INR FDA recently changed warfarin labeling to include genetic impact of its dosing Couma-Gen % Trial Design: Couma-Gen was a randomized trial of standard dosing warfarin (n = 99) or genotype-guided warfarin dosing (n = 101) in patients requiring oral anticoagulation. Personalized management regimen was based on pharmacogenetic variants CYP2C9 and VKORC1, and age, weight, and gender. Primary endpoint was percent out-of-range (OOR) international normalized ratios (INRs) through a mean of 46 days. Genotype- Guided Dosing Standard Dosing Percent OOR INRs (p = 0.47) Mean Dose Changes per Patient (p = 0.035) Circulation 2007;116:epub before print