Outline the pharmacology of warfarin.
The “traditional” pharmacology answer structure was useful to avoid omitting key details.
Warfarin is a synthetic coumarin derivative presented in tablet form for oral use . It is a racemic
mixture. S-enantiomer is 2-5 times more potent than the R-enantiomer. It is used for
anticoagulation and the usual dosing involves a loading dose ( 3 to 5 mg for 1 to 3 days) then
maintenance dose titrated to INR. It was expected answers would then detail mechanism of
action, absorption (commenting on bioavailability), distribution, elimination, excretion and
adverse effects. Warfarin has contraindications in pregnancy being teratogenic in first trimester
and increasing the risk of fetal haemorrhage in third trimester.
Better answers provided increased detail on mechanism of action including the initial
procoagulant effect due to protein C and S inhibition and some details about monitoring effect
with INR / PT.
Warfarin has several important drug interactions and detailing these gained additional marks.
Additional credit was given for discussion of reversal options, which includes 1) Stop
administration - days 2) Prothrombinex - hours 3) FFP - hours 4) Vitamin K depends on dose