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general anticoagulation guidelines

Before initiating warfarin Rx

Warfarin dosing principles

  • most hospital medication charts have a designated area for warfarin prescribing
  • the initiating doctor should document the indication, target INR and initial duration of Rx on the medication chart
  • ensure patient receives education and an anticoagulation booklet
  • look for drugs or herbal medications which may interact with warfarin Rx
  • whenever starting or stopping a drug which may interact (eg. antibiotics), re-check INR at 48-72hrs after the change - do not preempt a change, make dosage adjustments only after checking the INR otherwise you will be confused.
  • INR 2.5-3.5 for mechanical prosthetic heart valves
  • INR 2.0-3.0 for all other indications such as AF, DVT, PE, bio-prosthetic heart valves
  • consider life long if:
    • irreversible and clinically apparent hypercoagulable states such as DVT or PE with neoplastic disease
    • prosthetic heart valves
    • AF until risks outweigh its benefits
  • pulmonary embolism (PE) - 6 months if transient risk factor, 12 months if non-transient risk factor
    • 3 months if transient risk factor
    • 6 months if non-transient risk factor or unprovoked, then consider aspirin once warfarin ceased as appears to reduce risk of recurrence of DVT by a 1/3rd from 7.5%/yr down to 5.1%/yr 1)

Starting warfarin Rx

acute DVT/PE

  • overlap warfarin Rx with full dose heparin/enoxaparin Rx for minimum of 5 days.
  • ensure 2 consecutive days of INR > 2.0 are achieved before ceasing them.

chronic AF or valve replacements

post-operative patients

  • re-start with their “normal” pre-operative warfarin dose - do not reload!

initial warfarin dose

  • high loading doses such as 10mg should NOT be used as they may increase the risk of early bleeding
  • assess patient for risk factors of warfarin sensitivity and risk of bleeding:
    • “frail” elderly
    • low body weight
    • compromised nutrition
    • concomitant drugs which affect warfarin metabolism
    • any other bleeding risk such as hepatic impairment or severe heart failure
  • if no risk factors, start at warfarin 5mg nocte, otherwise consider smaller starting dose (2-4mg) and seek specialist advice
  • from Gedge et al Age Ageing 2000; 29: 31-34, as used by Western Health, 2008.
Day INR Warfarin dose
1 <1.4 5mg
2 <1.8 5mg
1.8-2.0 1mg
>2.0 nil
3 <2.0 5mg
2.0-2.5 4mg
2.6-2.9 3mg
3.0-3.2 2mg
3.3-3.5 1mg
> 3.5 nil
4 < 1.4 10mg
1.4-1.5 7mg
1.6-1.7 6mg
1.8-1.9 5mg
2.0-2.3 4mg
2.4-3.0 3mg
3.1-3.2 2mg
3.3-3.5 1mg
> 3.5 nil
>D4 use clinical judgement
anticoagulant_guidelines.txt · Last modified: 2014/08/26 22:50 (external edit)