The Influence of (R)- and (S)-Warfarin, Vitamin K and Vitamin K Epoxide upon Warfarin Anticoagulation

Summary The contribution of (R)and (S)-warfarin enantiomers, vitamin K and vitamin K epoxide and patient factors to inter-individual variability in daily warfarin requirements were examined in a group of 73 patients. Simple correlation analysis showed a significant positive relationship between INR values and plasma (S)-warfarin concentrations (r = 0.25; p = 0.038). Multivariate analysis for relationships with INR demonstrated a highly significant positive relationship between INR and (S)- warfarin (p = 0.004) and plasma vitamin K epoxide concentrations (p = 0.028), and a significant negative relationship between INR and plasma vitamin K concentrations (p = 0.034). Twenty five percent of variation in INR could be explained by these variables (adjusted R 2 = 0.25). Correlation analysis of data showed that warfarin dosage was significantly and negatively correlated with patient age (r = −0.42; p