The S isomer is 5 times more effective at inhibiting vitamin K epoxide reductase. The potency has to do with how effectively the isomers block vitamin K recycling by inhibiting vitamin K epoxide reductase. In general, coumarins block the formation of vitamin KH2 by inhibiting vitamin K epoxide reductase, limiting the gamma-carboxylation of the vitamin K–dependent coagulant proteins. This anticoagulant effect of coumarins can be overcome by low doses of vitamin K1 which bypasses vitamin K epoxide reductase.

dear @john

Thanks for your information. can we say Vitamin K antagonism of S-warfarine make it more potent, Can't say? Also enantiomers of Warfarine is processed by different enzymes. Can we say that it is responsible ?