Warfarin: Difference between revisions
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=Background= | ==Background== | ||
*Blocks activation of vitamin K dependent prothrombotic factors II, VII, IX, X | *Blocks activation of vitamin K dependent prothrombotic factors II, VII, IX, X | ||
*Blocks synthesis of vitamin K dependent antithrombotic proteins C and S | *Blocks synthesis of vitamin K dependent antithrombotic proteins C and S | ||
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*Contraindicated in pregnancy | *Contraindicated in pregnancy | ||
=Dosing= | ==Dosing== | ||
#Day 1: 5 - 7.5 mg oral at bedtime (to ensure absorption on empty stomach) | #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) | #Day 2 and beyond: 2.5 - 7.5 mg daily (usually 5 mg) | ||
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#Response also influenced by congestive heart failure, liver disease, Vitamin K deficiency, many drugs | #Response also influenced by congestive heart failure, liver disease, Vitamin K deficiency, many drugs | ||
=Target Range of INR= | ==Target Range of INR== | ||
#2.5 - 3.5: Mechanical prosthetic valves or recurrent thromboembolism | #2.5 - 3.5: Mechanical prosthetic valves or recurrent thromboembolism | ||
#2.0 - 3.0: All other indications | #2.0 - 3.0: All other indications | ||
=Complications= | ==Complications== | ||
#Bleeding | #Bleeding | ||
##Risk increased when INR >3 | ##Risk increased when INR >3 | ||
Revision as of 13:04, 10 June 2015
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 Also
Source
Tintinalli