Information 1–4

  • Therapeutic anticoagulation effect takes 2–3 days when first commencing warfarin
  • When immediate anticoagulation is required, concurrent parenteral anticoagulant is needed until INR is therapeutic
  • For stroke prevention in Atrial fibrillation warfarin is commenced without concurrent parenteral anticoagulant

Use in pregnancy

  • Avoid in pregnancy, safe during breastfeeding

1. Patient education

  • Always take the same brand of warfarin tablets unless advised by health professional
  • Take warfarin tablets at about the same time every day
  • Consider patient’s ability to break scored tablets when prescribing doses
  • Use a booklet to record the days after taking a dose so that any missed doses can easily be identified. See Resource 1.
  • Warfarin is affected by vitamin K which is found in certain foods e.g. green leafy
    vegetables. Eat a normal, balanced diet without dramatic changes, to keep intake of vitamin K stable
  • Avoid drinking large amounts of cranberry juice as this may increase the effects of warfarin
  • Maintain appointments for regular blood tests in case the dose of warfarin needs adjusting. The health professional will advise the next dose to take when the test result is known
Many medicines interact with warfarin. Always speak to the health professional before starting or stopping any medicines, vitamin supplements, herbal or over-the-counter products or marijuana. See Resource 2.
  • Contact a health professional if feeling unwell for any reason including:
    • unexplained bruising
    • bleeding
    • pink, red or dark brown urine
    • red or black faeces
    • bleeding from gums or nose
    • dizziness
    • trouble breathing or chest pain
    • severe headache
    • unusual pain or weakness
    • dark, purplish or mottled fingers or toes
    • vomiting or coughing up blood
    • excessive menstrual bleeding

2. Indications for therapy

Table 1. Indications for warfarin therapy duration and target INR 1–4

Indication

Minimum
recommended duration

Target
INR range

Deep vein thrombosis (DVT) or Pulmonary embolism (PE)

  • Dependent on specific clinical factors

2–3

Non-valvular Atrial fibrillation with CHA2DS2-VA score > 1

  • Indefinite

2–3

Elective cardioversion

  • 3 weeks before scheduled cardioversion and 4 weeks after successful cardioversion

2–3

After stent placement and CHA2DS2-VA score > 1

  • Indefinite. Anti-platelet agent combination therapy is short-term. Contact cardiac surgeon or cardiologist

2–3

Mitral stenosis

  • Indefinite

2–3

Mechanical prosthetic heart valves

  • Indefinite

2–3 for aortic

2.5–3.5 for mitral

Bioprosthetic (tissue) valves

  • 1–6 months post implant according to cardiologist

According to cardiologist

3. Initiating therapy

  • Use a warfarin recording form. See Resource 3.

Table 2. Regimen for initiation of warfarin 1-4

Day to take INR test

INR (target 2–3)

Daily warfarin dose until next INR test

Patients at LOW risk of thrombosis (i.e. Atrial fibrillation)

Day 1 initiation

Obtain baseline

  • 3 mg provided baseline INR < 1.4
  • If INR > 1.4 consider lower starting dose

Day 3

< 1.3

4 mg

1.3

3 mg

1.4

2.5 mg

1.5

2.5 mg

1.6

2 mg

1.7

2 mg

1.8

1.5 mg

1.9

1.5 mg

2

1.5 mg

2.1

1 mg

2.2

1 mg

2.3

0.5 mg

2.4

0.5 mg

2.5

0.5 mg

Day 3

> 2.5

  • Cease warfarin
  • Assess causes and indication
  • Repeat INR in 3–5 days
  • If warfarin indicated, restart at lower dose

Day 6 onwards then wkly

  • Continue INR monitoring until stabilised. See Table 3.

Patients at HIGH risk of thrombosis (e.g. DVT) with a short-acting parenteral anticoagulant during the first few days

Day 1 initiation

< 1.4

5 mg

Day 2

< 1.8

5 mg

1.8–2

1 mg

> 2

Nil

Day 3

< 2

5 mg

2–2.5

4 mg

2.6–2.9

3 mg

3–3.2

2 mg

3.3–3.5

1 mg

> 3.5

Nil

Day 4

< 1.4

10 mg

1.4–1.5

7 mg

1.6–1.7

6 mg

1.8–1.9

5 mg

2–2.3

4 mg

2.4–3

3 mg

3.1–3.2

2 mg

3.3–3.5

1 mg

> 3.5

Nil

Day 5 onwards

  • Continue INR monitoring until stabilised. See Table 3.
  • Minimum duration usually 3 months

Modify for patients with mechanical heart valves to target higher INR range of 2.5 – 3.5

4. INR monitoring frequency

  • Warfarin therapy requires regular monitoring of international normalised ratio (INR) levels
  • Consider alternative anticoagulant therapy for patients with a persistently high or labile INR

Table 3. INR monitoring frequency 2

INR

Low risk of thrombosis

High risk of thrombosis

< 2

  • Weekly until 2 consecutive results in target range
  • Daily until 2 consecutive results in target range

2–3

  • If 2 consecutive results in target range:
    • switch to fortnightlyfor a further 2–3 consecutive results in target range
    • then every 4 to 6 weeksif results remain in target range
  • If INR remains very stable, it is reasonable to extend monitoring frequency to 8 weeks
  • If 2 consecutive results in target range:
    • switch to 3–5 days for a further 2 consecutive results in target range
    • then weekly for a further 2–3 consecutive results in target range
    • then fortnightlyfor a further 2–3 consecutive results in target range
    • then every 4 to 6 weeks if results remain in target range
  • If INR remains very stable, it is reasonable to extend monitoring frequency to 8 weeks

> 3

  • Every 2–3 days until 2 consecutive results in target range
  • Daily until 2 consecutive results in target range

Modify for patients with mechanical heart valves to target higher INR range of 2.5 – 3.5

5. Maintenance therapy

  • For use after stabilisation or following initiation
  • Recommendations are based on compliance with total weekly warfarin regimen and consistent diet

Table 4. Warfarin dosing regimen for INR target range of 2–3 2

INR

Dosage adjustment

 

< 1.5

  • Increase wkly dose by 20% averaged out over the week

Recheck INR according to Table 3.

1.5 – 1.9

  • Increase wkly dose by 10% averaged out over the week

2 – 3

  • Target INR range. No change required

3.1 – 3.4

  • Decrease wkly dose by 10% averaged out over the week OR
  • No change depending on clinical judgement of previous INR results

3.5 – 3.9

  • Consider omitting one dose AND
  • Decrease wkly dose by 20% averaged out over the week

4 – 4.5

  • Decrease wkly dose by 20% averaged out over the week OR
  • Withhold next dose based on risk factors for increased sensitivity to warfarin

> 4.5

  • Refer to 6. Managing bleeding or overdose. See Table 5.

Modify for patients with mechanical heart valves to target higher INR range of 2.5 – 3.5

6. Managing bleeding or overdose

  1. Patient risk factors 1–4
    • Consider admission for specialist treatment (e.g. blood products) and monitoring
    • Patient risk factors for increased risk of bleeding during warfarin therapy are:
      • > 75 years age
      • medical history of bleeding
      • baseline INR >1.4
      • concomitant drugs affecting warfarin metabolism. See Resource 3.
      • comorbidities i.e. Hypertension, Stroke and transient ischaemic attack, Coronary heart disease, Chronic kidney disease, hepatic impairment, low platelets or cancer
      • major surgery within last 2 weeks
      • patients nil by mouth, not eating or malnourished
  2. Management of bleeding 1–4
  • Reverse anticoagulation effects of warfarin according to Table 5.
  • Management options include Vitamin K, Prothrombin complex concentrate (PCC) or Fresh frozen plasma (FFP)

Table 5. Management of bleeding or warfarin overdose 2

Presentation

Recommendations

Life-threatening or critical organ bleeding and INR > 1.5

  • CEASE WARFARIN. Seek specialist advice. Give:
    • phytomenadione (vitamin K #) 5–10 mg IV and
    • fresh frozen plasma (FFP) 150–300 mL and
    • prothrombin complex concentrate (PCC. See Anticoagulant Guideline for Hospitalised Adult Patients. Resource 4. )
      • if PCC unavailable increase FFP dose to 15 mL/kg
  • Assess INR frequently until clinically stable.

Clinically significant bleeding i.e. not life-threatening or associated with a critical organ and INR > 1.5

  • CEASE WARFARIN. Seek specialist advice. Give:
    • phytomenadione (vitamin K #) 5–10 mg IV and
    • PCC (See Anticoagulant Guideline for Hospitalised Adult Patients. See Resource 4.)
      • if PCC unavailable, give FFP 15 mL/kg.
  • Assess INR frequently until clinically stable

Minor bleeding with any INR

  • Omit warfarin
  • Repeat INR the following day and adjust dose to target INR in therapeutic range according to Table 4.
  • If bleeding risk is high Φ or INR is > 4.5 consider:
    • phytomenadione (vitamin K #) 1–2 mg orally or 0.5–1 mg IV

No Bleeding and INR > 10

  • CEASE WARFARIN. Seek specialist advice. Give:
    • phytomenadione (vitamin K #) 2–5 mg orally (note: the higher dose can lead to delayed therapeutic INR target range when recommencing warfarin) or 0.5–1 mg IV
      • check INR in 12–24 hours if only vitamin K administered
    • If bleeding risk is high Φ consider PCC (See Anticoagulant Guideline for Hospitalised Adult Patients. Resource 4.)
      • check INR at 30–60 minutes and 12–24 hours if PCC has been administered. Monitor every 1–2 days for a week
  • Resume lower dose once INR approaches therapeutic range

No Bleeding and INR 4.5 – 10

  • Cease warfarin
  • Address reasons for elevated INR and 6.1 Patient risk factors
  • If bleeding risk is high Φ give:
    • phytomenadione (vitamin K #) 1–2 mg orally or 0.5–1 mg IV
    • check INR in 12–24 hours
  • Resume lower dose once INR approaches therapeutic range

No Bleeding  and INR > therapeutic range but < 4.5

  • Reduce or withhold next dose of warfarin based on 6.1 Patient risk factors
  • Resume lower dose once INR approaches therapeutic range
  • If INR is minimally above therapeutic range (i.e. within 10%) dose reduction is generally not necessary
  • # Konakion MM®, the IV preparation of phytomenadione (vitamin K), may be given orally. It is NOT for intramuscular injection
  • Φ High bleeding risks are a major bleed within last 4 weeks, surgery within last 2 weeks, thrombocytopenia with a platelet count < 50 × 109/L, liver disease or concurrent antiplatelet or NSAID use

7. Considerations 1–4

  • Stroke and bleeding risk factors will change due to ageing, comorbidities or lifestyle changes
  • Assess HAS-BLED and CHA2DS2-VA frequently throughout treatment
  • Non-vitamin K oral anticoagulants (NOACs; apixaban, dabigatran or rivaroxaban) are recommended in preference to warfarin as they are:
    • as good as or better than warfarin in reducing stroke and systemic embolism
    • have a lower risk of intracranial haemorrhage as a side effect
    • easier for patients and clinicians to manage and use
    • if a patient is already on warfarin it is reasonable to change to NOAC if indicated
  • Antiplatelet therapy is not recommended for long-term secondary prevention of stroke in patients with atrial fibrillation regardless of stroke risk
  • In patients without Atrial fibrillation or another source of cardiogenic embolism, the use of warfarin is not recommended

8. References

9. Resources

  1. Patient warfarin monitoring and education booklet
  2. Warfarin drug interactions
  3. Non-inpatient rural and remote warfarin record
  4. Anticoagulant Guideline for Hospitalised Adult Patients
  5. Management of warfarin in the community

Last updated: September 2024

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