Warfarin | Heparin | |
---|---|---|
Chemistry | Coumarin derivative | Mucopolysaccharide |
Source | Synthetic | Hog lung, pig intestine |
Route of administration | Oral | Parenteral (i.v., s.c.) |
Onset of action | Delayed (1–3 days) | Immediate |
Duration of action | 3–6 days | 4–6 hrs |
Activity | In vivo only | In vitro and in vivo |
Mechanism | Inhibits synthesis of clotting factors | Blocks action of factor X and thrombin |
Antagonist | Vit K | Protamine sulphate |
Variability in response | Marked | Limited |
Lab control | Prothrombin time/INR (essential) | aPTT/clotting time (desirable) |
Drug interactions | Many and significant | Few and not significant |
Use | For maintenance | To initiate therapy |