see also:

• anticoagulants
• antithrombotic Rx for prevention of stroke
• Mx of PE
• Mx of excessive anticoagulation, high INR, or bleeding on warfarin Rx

derived from: Western Health guidelines on warfarin Rx (pdf) - only available within WH intranet

• consider if the benefits of anticoagulation outweigh its risks, such as bleeding, for each patient
  • see antithrombotic Rx for prevention of stroke if patient has atrial fibrillation
  • CHA2DS2-VASc score for determining stroke risk in patients with non-valvular AF
  • HAS-BLED bleeding risk scoring tool for anticoagulation Rx
• ensure baseline INR, platelet count, and LFT's are all normal - if not, seek specialist advice

• 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
• DVT:
  • 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⁾

• 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.

• start warfarin alone, although can overlap with prophylactic heparin or enoxaparin

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

• 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.