Starting Warfarin

Day

INR* 

Warfarin dose (mg)

1.

<1.4

10

2.

< 1.8

10

1.8

1

> 1.8

0.5

3.

< 2.0

10

2.0 – 2.1

5

2.2 – 2.3

4.5

2.4 – 2.5

4

2.6 – 2.7

3.5

2.8 – 2.9

3

3.0 – 3.1

2.5

3.2 – 3.3

2

3.4

1.5

3.5

1

3.6 – 4.0

0.5

> 4.0

0

4.

<1.4

> 8

1.4

8

1.5

7.5

1.6 – 1.7

7

1.8

6.5

1.9

6

2.0 – 2.1

5.5

2.2 – 2.3

5

2.4 – 2.6

4.5

2.7 – 3.0

4

3.1 – 3.5

3.5

3.6 – 4.0

3

4.1 – 4.5

Miss out next day’s dose then give 2mg

> 4.5

Miss out 2 days doses then give 1 mg

INR  -  International Normalized Ratio

APTT -  activated partial thromboplastin time

*APTT should be within or below therapeutic range (1.5 – 2.5 x control).  If APTT is above this range, the heparin effect on INR should be neutralised by adding protamine (0.4 mg / ml plasma) to the sample.

Reference:

Drug and Therapeutics Bulletin 1992; 30: 77 – 80

Fennerty A et al, Anticoagulants  in venous thromboembolism.  BMJ 1988; 297: 1285 - 8