Heparin vs. Warfarin

Heparin: activates plasma antithrombin III; blocks thromboplastin generation; neutralizes tissue thromboplastin. Administered subcutaneously and I.V. Onset is immediate, and duration is 4 hours for subcutaneous administration. Protein binding and metabolism is in liver by heparinase; inactive metabolite is excreted by the kidney. Antagonists for heparin are protamine sulfate, a strongly basic protein, which forms a complex with heparin to an inactive compound; 1mg protamine for 100 units of heparin.


Warfarin: inhibits the synthesis of liver factors II, VII, IX and X by blocking the action of vitamin K. It is given orally. Onset takes at least 2 days (MD must moniter INR and adjust for the target INR), and duration of action is 2-10 days. Warfarin is bound to albumin (99% - if you give a drug to displace warfarin it frees up the warfarin to act on the liver), side-chain reduction to alcohol (dextrowarfarin), oxidation to 7-hydroxywarfarin (levowarfarin). Antagonists are vitamin K and fresh plasma.

Category: Pharmacology Notes