|
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).