Warfarin
- The most frequently prescribed oral anticoagulant
- Mechanism of action:
Therapeutic dose --> Carboxylation of synthesizing factors impaired --> Vitamin K antagonism --> 30 -50% synthesis
of factor II, VII, IX, X, and of endogenous anticoagulants Protein C & S.
--> Carboxylation of secreted factors impaired --> functional deficiency of factors.
- Pharmacokinetics:
Reaches plasma in 1 hr; peaks in 2 - 8 hrs.
99% bound to albumin
Metabolized in liver and kidneys: inactive metabolites secreted in urine and stool
Mean t1/2: 40 hrs
Duration of effect 2 - 5 days
After impairing the release of new factors, the anticoagulant effect depends on the t1/2 of already circulating normal
factors:
Protein C 8 hrs
FVII 6 hrs
FII 50 hrs
- Effects:
Anti-coagulant (Preventive)
Anti-thrombotic (Therapeutic)