Anticoagulation Using Warfarin
by Margaret A. Fitzgerald, MS, RN, CS, FNP,
Deanna S. Kania, PharmD, and Ron A. Weathermon, PharmD
Edited by Marty Couret, RN, MSN
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Initiating Warfarin Therapy
- Starting doses for warfarin are usually between 5 - 7.5 mg.
- Prescriptions should have orders to take warfarin in the evening.
- Loading doses is no longer recommended.
- The condition being treated corresponds to the therapeutic INR range (see Table 1).
- The condition also determines the duration of the therapy needed (see Table 2).
Table 1 - Therapeutic INR Range
Baseline INR < 1.5 |
Dosage |
Standard Dose |
7.5 mg |
Patient weight < 100 lbs. |
5 mg |
Patient age > 65 years |
5 mg |
Baseline INR > 20 |
NO dose - determine cause of elevation
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Table 2 - Indications and Length of Warfarin Treatment
Condition |
INR |
Duration of therapy |
Acute venous thrombosis |
First episode |
2 - 3 |
3 - 6 months |
High risk of recurrence |
2 - 3 |
Indefinitely |
In presence of antiphospholipid antibody |
3 - 4 |
Life-long |
Prevention of systemic embolis |
Tissue heart valves |
2 -3 |
3 months |
Valvular heart disease after thrombotic event |
2 - 3 |
Indefinitely |
Mechanical heart valve |
2.5 - 3.5 |
Indefinitely |
Acute myocardial infarction |
2 - 3 |
As deemed by clinical presentation |
Atrial fibrillation |
Chronic or intermittent |
2 - 3 |
Lifelong |
Cardioversion |
2 - 3 |
3 weeks before and 4 weeks after conversion to sinus rhythm |
Reference:
Horton, J., Bushwick, B. (1999) Warfarin therapy: Evolving strategies in anticoagulation. American Family Physician. 59 (3) 635-647.
Laboratory Monitoring Guidelines
- INR Monitoring based on stability of the patient
- Check INR 2-3 times a week then,
- Check INR weekly for two weeks then,
- Check INR every 4-6 weeks if INR is stable
- Patients are considered stable if they have had two consecutive INRs that have not required dosage change.
- Re-check INR no more than 2 weeks after a dose change.
- Other Laboratory Monitoring
- CBC should be checked every 6-12 months
- A urinalysis and hemocult test recommended annually
Reference:
Kania, D. S., Weathermon, R. A.. Anticoagulation monitoring. Notes from clinical skills course 581.
INR Goal 2 - 3
Patient's INR Level |
Action |
Comment |
At desired range |
Repeat INR at interval determined by duration of therapeutic INR and underlying condition
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Repeat INR in
- 4-6 weeks with stable condition and long-term therapeutic INR
- At least weekly when underlying condition can impact coagulation state (malignancy, clotting disorder, use of medications that can influence warfarin effect)
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INR< 2 |
- Increase weekly dose by 5-20%
- Repeat INR 2-3 times/ week until within desired range
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Check for
- adherence to recommended therapy
- Use of medications or foods that may interfere with warfarin effect
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INR 3-3.5 |
- Decrease weekly dose by 5-15%
- Repeat INR 2-3 times/ week until within desired range
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Check for
- Adherence to recommended therapy
- Use of medications or foods that may enhance warfarin effect
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INR 3.6-4 |
- Consider withholding 1 dose, decrease weekly dose by 10-15%
- Repeat INR 2-3 times/ week until within desired range
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Check for
- Adherence to recommended therapy
- Use of medications or foods that may enhance warfarin effect
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INR >4 without complications and no indication for rapid reversal of anticoagulation effect |
- Consider withholding 1 dose, decrease weekly dose by 10-20%
- Repeat INR 2-3 times/ week until within desired range
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Check for
- Adherence to recommended therapy
- Use of medications or foods that may enhance with warfarin effect
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INR > 4 and need for rapid reversal of anticoagulant effect |
Vitamin K 3 mg SC or slow IV |
- Check INR at 6 and 24 hours
- May repeat dose
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Resource:
Horton, J., Bushwick, B. (1999) Warfarin therapy: Evolving strategies in anticoagulation. American Family Physician. 59 (3) 635-647.
INR 2.5 - 3.5
Patient's INR Level |
Action |
Comment |
At desired range |
- Repeat INR at interval determined by duration of therapeutic INR and underlying condition
- Repeat INR 2-3 times/ week until within desired range
|
Repeat INR in
- 4-6 weeks with stable condition and long-term therapeutic INR
- At least weekly when underlying condition can impact coagulation state; malignancy, clotting disorder, use of medications that can influence warfarin effect
|
INR< 2 |
- Increase weekly dose by 10-20%
- Repeat INR 2-3 times/ week until within desired range
|
Check for
- Adherence to recommended therapy
- Use of medications or foods that may interfere with warfarin effect
|
INR 2- 2.4 |
- Increase weekly dose by 5-15%
- Repeat INR 2-3 times/ week until within desired range
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Check for
- Adherence to recommended therapy
- Use of medications or foods that may interfere with warfarin effect
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INR 3.5-4.6 |
- Decrease weekly dose by 5-15%
- Repeat INR 2-3 times/ week until within desired range
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Check for
- adherence to recommended therapy
- Use of medications or foods that may enhance with warfarin effect
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INR 4.7-5.2 |
- Consider withholding 1 dose, decrease weekly dose by 10-20%
- Repeat INR 2-3 times/ week until within desired range
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Check for
- Adherence to recommended therapy
- Use of medications or foods that may enhance with warfarin effect
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INR >5.2 without complications and no indication for rapid reversal of anticoagulation effect |
- Consider withholding 1-2 doses, decrease weekly dose by 10-20%
- Repeat INR 2-3 times/ week until within desired range
|
Check for
- Adherence to recommended therapy
- Use of medications or foods that may enhance with warfarin effect
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INR > 5.2 and need for rapid reversal of anticoagulant effect |
Vitamin K 3 mg SC or slow IV |
- Check INR at 6 and 24 hours
- May repeat dose
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Resource:
Adapted from: Horton, J., Bushwick, B. (1999) Warfarin therapy: Evolving strategies in anticoagulation. American Family Physician. 59 (3) 635-647. |
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