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Warfarin
Aka: Warfarin, Coumadin, Anticoagulation after Heart Valve Replacement, Valve Replacement and Anticoagulation, Vitamin K Antagonist
- See Also
- Coumadin Drug Interactions
- Coumadin Protocol
- Coumadin Protocol for the Perioperative Period
- Heparin
- Anticoagulation
- Direct Oral Anticoagulant
- Definitions
- Vitamin K Antagonist
- Agents that inhibit the intrahepatic intercoversion of Vitamin K to its reduced form
- In the absence of Vitamin K Clotting Factors/proteins are not activated and Clotting Cascade does not occur
- Warfarin is the most commonly used Vitamin K Antagonist
- Other Vitamin K Antagonists include Dicumarol, phenprocoumon and acenocoumarol
- Mechanism
- Inhibits Vitamin K participation in factor synthesis (Vitamin K Antagonist)
- Clotting Factors (both pro-coagulant and Anticoagulant) are Vitamin K Dependent
- Vitamin K is required for carboxylation of terminal ends of coagulation proteins
- Without carboxylation, Clotting Factors/proteins are not activated and Clotting Cascade does not occur
- Warfarin inhibits the intrahepatic cyclic interconversion of Vitamin K to a reduced form
- Keeps Vitamin K and dependent factors inactive
- Vitamin K dependent coagulation proteins
- Procoagulant Activity (1972)
- Factor 10 (36 hour half life)
- Factor 9 (24 hour half life)
- Factor 7 (8 hour half life)
- Factor 2 (50-72 hour half life)
- Anticoagulant Activity
- Protein C (8-14 hour half life)
- Protein S (30-42 hour half life)
- Coumadin has an initial paradoxical procoagulant effect
- Anticoagulant factors are depleted first
- Initially both Hypercoagulable and at increased risk for Warfarin skin necrosis
- Concurrently administer Heparin for first 4-5 days
- Indications: Standard INR between 2.0 and 3.0
- Precautions
- INR 2.2 to 2.3 associated with lowest overall mortality
- Oden (2002) BMJ 325:1073-5 [PubMed]
- Major orthopedic surgery
- Hip replacement or ORIF Fracture (for 28-35 days)
- Elective total knee arthroplasty (for 10-14 days)
- Atrial Fibrillation
- High CVA risk (CHADS Score 2 or higher)
- Persistent, paroxysmal Atrial Fibrillation, flutter
- Cardioversion (Warfarin for 3 weeks before, 4 weeks after)
- Mitral Stenosis
- Coronary Stent and high CVA risk (CHADS Score 2 or higher)
- Warfarin is continued indefinately AND
- Antiplatelet agents
- First - Immediately after stenting: Triple Therapy
- Clopidogrel AND Aspirin (and Warfarin)
- Continue triple therapy for 1 month following bare metal stent
- Continue triple therapy for 3-6 months following drug eluting stent
- Next - Following initial period of triple therapy: Dual Therapy
- Clopidogrel OR Aspirin (and Warfarin) until 12 months following stenting
- Next - Following first year of antiplatelet drugs
- Continue Warfarin alone
- Venous Thromboembolism (Deep Vein Thrombosis or Pulmonary Embolism)
- First episode with reversible risks: 3 months
- First episode and idiopathic: 6-12 months
- Cancer: LMWH x3-6 months, then Warfarin longterm
- Antiphospholipid Antibody (Lupus Anticoagulant): 12 months or longterm
- Two Thrombophilias: 12 months or longterm
- Clotting disorder related: 6-12 months or longterm
- Two or more episodes: Longterm
- Coronary Artery Disease
- High risk patients for Myocardial Infarction without stent
- Continue Warfarin for 3 months following Myocardial Infarction
- Continue with low dose Aspirin (e.g. 81 mg)
- High risk patients for Myocardial Infarction with bare metal stent
- First: Triple therapy (Warfarin AND Clopidogrel AND low dose Aspirin) for 1 month
- Next: Dual therapy (Warfarin AND Clopidogrel or low dose Aspirin) for 2 months
- High risk patients for Myocardial Infarction with drug eluting stent
- First: Triple therapy (Warfarin AND Clopidogrel AND low dose Aspirin) for 3-6 months
- Heart Valve Replacement
- Mechanical Aortic Valve Replacement with bileaflet or tilting disk valves
- Low dose Aspirin (e.g. 81 mg) is recommended with Warfarin if low bleeding risk
- Bioprosthetic Heart Valve in mitral position
- Warfarin for 3 months after insertion
- Indications: Target INR between 2.5 and 3.5
- Mechanical Heart Valves
- Ball and cage valve
- Comorbid Atrial Fibrillation, CHF, MI, LAE
- Mitral Valve Replacement
- Dosing Protocol
- See Coumadin Protocol
- References
- (2012) Chest 141(suppl 2) [PubMed]
- Wigle (2013) Am Fam Physician 87(8): 556-66 [PubMed]