Part One: Warfarin Dosing Guidelines

Conversion from Heparin to Warfarin

• May begin concomitantly with heparin therapy

• Heparin should be continued for a minimum of four days

• Time to peak antithrombotic effect of warfarin is delayed 96 hours (despite INR)

• When INR reaches desired therapeutic range, discontinue heparin (after a minimum of four days)

Notes:

When short-term heparin followed by long-term warfarin are used, both anticoagulants can be started simultaneously. Heparin should be continued for a minimum of four days because the peak antithrombotic effect of warfarin is delayed for about 96 hours, independently of the INR, until Factor II (prothrombin is reduced). Heparin can be discontinued after a minimum of four days when the INR reaches the therapeutic range.

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About this presentation:

The content of these pages is from a presentation called  "Management of Oral Anticoagulant Therapy: Principles & Practice," prepared by the American Heart Association's Post-Graduate Education Committee of the Council on Clinical Cardiology.  Supported by an educational grant from DuPont Pharmaceuticals.

Authors: Jack Ansell, M.D., Jack Hirsch, M.D., Nanette K. Wenger, M.D.

Data current as of October 1999.

Endorsed by the Anticoagulation Forum and the American Heart Association Council on Atherosclerosis, Thrombosis, and Vascular Biology.

The entire PowerPoint presentation is available from the American Heart Association.