Warfarin Induction Protocol for Inpatients

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A guideline is intended to assist healthcare professionals in the choice of disease-specific treatments.

Clinical judgement should be exercised on the applicability of any guideline, influenced by individual patient characteristics. Clinicians should be mindful of the potential for harmful polypharmacy and increased susceptibility to adverse drug reactions in patients with multiple morbidities or frailty.

If, after discussion with the patient or carer, there are good reasons for not following a guideline, it is good practice to record these and communicate them to others involved in the care of the patient.

In-patient Warfarin Induction Protocol Age-adjusted Fennerty Regimen

Day  

INR

Warfarin dose (mg) depending on age – to be given once daily at 6pm

50 years

51-65 years

66-80 years

>80 years

1

<1.4

10

9

7.5

6

 

2

<1.6

10

9

7.5

6

1.6

0.5

0.5

0.5

0.5

 

 

 

 

 

3

<1.8

10

9

7.5

6

1.8-2.5

4.0-5.0

3.5-4.5

3.0-4.0

2.5-3.0

2.6-3.0

2.5-3.5

2.5-3.5

2.0-2.5

1.5-2.0

3.1-3.5

1.0-2.0

1.0-2.0

0.5-1.5

0.5-1.5

3.6-4.0

0.5

0.5

0.5

0.5

>4

0

0

0

0

 

 

 

 

 

4

<1.6

10.0-15.0

9.0-13.0

7.5-11.0

6.0-9.0

1.6-1.9

6.0-8.0

5.5-7.0

4.5-6.0

3.5-5.0

2.0-2.6

4.5-5.5

4.0-5.0

3.5-4.5

2.5-3.5

2.7-3.5

3.5-4.0

3.0-3.5

2.5-3.0

2.0-2.5

3.6-4.0

3

2.5

2

1.5

4.1-4.5

Omit today’s dose then:

 

1.0-2.0

0.5-1.5

0.5-1.5

0.5-1.0

>4.5

Withhold warfarin until INR <3.0, then restart on 0.5-1.0

Consider reducing dose by 33% if the patient is on amiodarone, has severe congestive heart failure (EF<30% or biventricular failure), has abnormal LFT’s or has severe oxygen-dependant COPD.

Perform baseline INR, and then daily for first 4 days.

When the INR result is towards the upper end of a range in the INR column, it is recommended that a warfarin dose is chosen towards the lower end of the suggested range in the age-appropriate dose column; and vice versa when INR result is towards the lower end of an INR range.

Beyond day 4, dosage adjustment may still be required, especially between days 5 and 14 when INR may need to be assessed every 2-3 days until stable and patient has been transferred to an appropriate outpatient monitoring service.

More careful dosing and monitoring may be required in elderly patients or where there is co-administration with drugs known to increase or decrease INR (consult BNF or seek advice from clinical pharmacist).

Last reviewed: 02 March 2021

Next review: 30 September 2022

Author(s): Dawn Kyle, Linda Smith

Version: 5

Author Email(s): [email protected], [email protected]

Approved By: Area Drugs and Therapeutics Committee

Document Id: 27