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 R2 = 0.25). Correlation analysis of data showed that warfarin dosage was significantly
and negatively correlated with patient age (r = −0.42; p <0.0001). Patient age accounted
for 25% of variation in warfarin dosage requirements (R2 = 0.25). The combined effects of age and vitamin K appear to account for much of
the inter-individual variability in warfarin dosage requirements.
Keywords
Warfarin - anticoagulation - vitamin K - vitamin K epoxide - ageing
