View source for Warfarin

=Background=
*Blocks activation of vitamin K dependent prothrombotic factors II, VII, IX, X
*Blocks synthesis of vitamin K dependent antithrombotic proteins C and S
*Because of differing factor half-lives, can cause transient (24-36 hour) prothrombosis at start of therapy
**Bridge with heparin for 1-2 days until INR is in desired range
*Albumin bound
*Metabolized by liver
*Contraindicated in pregnancy

=Dosing=
#Day 1: 5 - 7.5 mg oral at bedtime (to ensure absorption on empty stomach)
#Day 2 and beyond: 2.5 - 7.5 mg daily (usually 5 mg)
#INR increase of >0.3 - 0.4 per day requires dose reduction
#Response also influenced by congestive heart failure, liver disease, Vitamin K deficiency, many drugs

=Target Range of INR=
#2.5 - 3.5: Mechanical prosthetic valves or recurrent thromboembolism
#2.0 - 3.0: All other indications

=Complications=
#Bleeding
##Risk increased when INR >3
##Exponential increase when INR >5
##Avoid giving NSAIDs, sulfas, macrolidies (azithromycin ok), fluoroquinolones
#Skin necrosis
##Usually in patient with protein C deficiency
##Occurs 3 - 8 days after starting treatment
##Treatment: stop warfarin, start parenteral anticoagulant, give Vitamin K1 (See [[Warfarin (Coumadin) Reversal]])

==Reversal==
*See [[Warfarin (Coumadin) Reversal]]

==See Also==
*[[Coagulopathy (Main)]]

==Source ==
Tintinalli

[[Category:Drugs]]
[[Category:Heme/Onc]]