Warfarin Guidelines for Initiation in Adults
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Objectives
The purpose of this guideline is to provide dosing assistance for initiating warfarin therapy in patients that have not previously been on warfarin.
University of Michigan Health System
Anticoagulation Program
Guideline for Initiating Oral Warfarin in Adult Inpatients
Loading doses of warfarin (e.g., 10 mg on days 1 and 2) are no longer recommended.
Several controlled studies have shown that starting patients on 5 mg of warfarin daily achieves a therapeutic anticoagulant effect as rapidly as 10 mg loading regimens while causing fewer supratherapeutic INRs. The following algorithm by Crowther and colleagues should guide the dosing of warfarin during the first several days of therapy.
Nomogram for Starting Patients on Warfarin*
|
|
INR |
Dosage |
|
DAY 1 |
A baseline INR must be obtained prior to starting warfarin |
5 mg** |
|
DAY 2 |
<1.5 1.5 - 1.9 2.0 - 2.5 > 2.5 |
5 mg 2.5 mg 1 - 2 mg 0 mg |
|
DAY 3 |
<1.5 1.5 - 1.9 2.0 - 3.0 > 3.0 |
5 - 10 mg 2.5 - 5 mg 0 - 2.5 mg 0 mg |
|
DAY 4 |
< 1.5 1.5 - 1.9 2.0 - 3.0 > 3.0 |
10 mg 5 -7.5 mg 0 - 5 mg 0 |
|
DAY 5 |
< 1.5 1.5 - 1.9 2.0 - 3.0 > 3.0 |
10 mg 7.5 - 10 mg 0 - 5 mg 0 |
|
DAY 6 |
< 1.5 1.5 - 1.9 2.0 - 3.0 > 3.0 |
7.5 - 12.5 mg 5 - 10 mg 0 - 7.5 mg 0 |
*This algorithm can be used in patients currently receiving unfractionated heparin or low molecular weight heparin (LMWH).
**In select patients (e.g., very large or frail patients, those on medications known to interact with warfarin, elderly, and those with heart failure or liver failure), a Day 1 warfarin dose different from 5mg may be appropriate.
Due to the uncertain clinical benefit and cost of the pharmacogenetic tests, their routine use is not recommended to guide warfarin dose initiation or adjustment.