warfarin - vit K reductase inhibitor 

Warfarin indications 

• mechanical valve anticoagulation, target INR 2.5-3.5 

• AF , usual target INR 2-3 

• VTE 

Mechanism of warfarin 

• following intiation of warfarin, liver produces defective clotting factor. 

• However, anticogulant effect will not be established until pre-existing factors are washed out, which takes 5-7 days

• Also inteferes which anticoagulant protein c and protein s - they have shorter half life, hence initially warfarin can have procoagulant effect 

warfarin half life - 10-12 hours 

take time to reach target INR 

when initiate, can be precoagulant instead of blood thinning 

Hence: clexane 40mg + warfarin 5mg OD for 3 days, until reach taget INR, then stop clexane. 

If supratherpeutic INR, may need reduced dose of warfarin

if INR too high, vit K stat dose

DVT 

virchow's triad 

PE

clexane prophylatic dose - 40mg OD

treatment dose -