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Oral Anticoagulants | Dosing Protocol

Purpose: To start warfarin therapy in a patient with deep vein thrombosis using the algorithm of Fennerty et al.

Description

Fennerty et al developed a protocol for starting oral anticoagulant therapy in a patient being treated with intravenous heparin for deep vein thrombosis. This can help prevent the overdosing of a patient that can occur when a single loading dose is given for several consecutive days. The authors are from Llandough Hospital in South Glamorgan and the Welsh National School of Medicine in Cardiff.


Goal: To provide adequate oral anticoagulation by day 4 and to identify the appropriate maintenance dose.

 

Day 1 of warfarin (typically Day 3 of a heparin infusion): With the patient's INR < 1.4, give 10 mg warfarin at 5 PM (17:00).

 

where:

• I am not quite sure what is done if the INR is >= 1.4.

 

Day 2: Determine the INR 16 hours after first dose (9 AM). Dose warfarin at 5 PM according to the following table:

 

INR

Dose Warfarin to Give

< 1.8

10 mg

1.8

1 mg

> 1.8

0.5 mg

 

Day 3: Determine the INR 16 hours after second dose (9 AM). Dose warfarin at 5 PM according to the following table:

 

INR

Dose Warfarin to Give

< 2.0

10.0

2.0 – 2.1

5.0

2.2 – 2.3

4.5

2.4 - 2.5

4.0

2.6 – 2.7

3.5

2.8 – 2.9

3.0

3.0 – 3.1

2.5

3.2 – 3.3

2.0

3.4

1.5

3.5

1.0

3.6 – 4.0

0.5

> 4.0

0

 

Day 4: Determine the INR 16 hours after third dose (9 AM). Dose warfarin at 5 PM according to the following table that lists the subsequent maintenance dose.

 

INR

Maintenance Dose of Warfarin in mg

< 1.4

> 8.0

1.4

8.0

1.5

7.5

1.6 – 1.7

7.0

1.8

6.5

1.9

6.0

2.0 – 2.1

5.5

2.2 – 2.3

5.0

2.4 – 2.6

4.5

2.7 – 3.0

4.0

3.1 – 3.5

3.5

3.6 – 4.0

3.0

4.1 – 4.5

2.0 (hold dose day 5)

> 4.5

1.0 (hold dose days 5 and 6)


 


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Specialty

Objective

ICD-10