Genotype-guided warfarin therapy: Still of only questionable value two decades on.

Since 60% of inter-individual variability in warfarin dose/response is due to other factors (many of which are non-genetic), expectations of eliminating this variability simply by CYP2C9/VKORC1 genotyping are over-optimistic and efforts cost-ineffective. Real-world studies have not always corroborated trials-based claims of clinical benefit. It is time to consider redirecting scarce resources away from the study of warfarin pharmacogenetics to pharmacogenetic research of potentially greater clinical relevance.