Warfarin: Difference between revisions

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


==Dosing==
=Dosing=
#Day 1: 5-7.5 mg po QHS (to ensure absorption on an empty stomach)
#Day 1: 5 - 7.5 mg oral at bedtime (to ensure absorption on empty stomach)
##2.5-7.5 mg thereafter (most often 5 mg)
#Day 2 and beyond: 2.5 - 7.5 mg daily (usually 5 mg)
#Increase in INR of >0.3-0.4 units per day necessitates dose reduction
#INR increase of >0.3 - 0.4 per day requires dose reduction
#CHF, liver disease, Vitamin K def, drugs may influence warfarin response
#Response also influenced by congestive heart failure, liver disease, Vitamin K deficiency, many drugs


==Range (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 is increased when INR is in 3-4.5 range
##Risk increased when INR >3
##Exponential increase occurs when INR is >5
##Exponential increase when INR >5
##Avoid giving pts NSAIDs, sulfas, macrolidies (azithromycin ok), fluoroquinolones
##Avoid giving NSAIDs, sulfas, macrolidies (azithromycin ok), fluoroquinolones
#Skin necrosis
#Skin necrosis
##Primarily occurs in pts w/ protein C deficiency
##Usually in patient with protein C deficiency
##Occurs 3-8d after starting treatment
##Occurs 3 - 8 days after starting treatment
##Treatment
##Treatment: stop warfarin, start parenteral anticoagulant, give Vitamin K1 (See [[Warfarin (Coumadin) Reversal]])
###Discontinue warfarin; start parenteral anticoagulant
###Vitamin K1 administration


==Reversal==
==Reversal==

Revision as of 19:49, 24 August 2013

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

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

Target Range of INR

  1. 2.5 - 3.5: Mechanical prosthetic valves or recurrent thromboembolism
  2. 2.0 - 3.0: All other indications

Complications

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

Reversal

Source

Tintinalli

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