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THERAPEUTIC CONTROVERSIES

Initiating Warfarin Therapy: 5 mg versus 10 mg

Clinical Associate, Department of Pharmacy Practice, University of Illinois at Chicago, Chicago, IL

Robert J DiDomenico, PharmD

Clinical Assistant Professor, Department of Pharmacy Practice; Affiliate Faculty, Center for Pharmacoeconomic Research, University of Illinois at Chicago

Nancy L Shapiro, PharmD BCPS

Clinical Assistant Professor, Department of Pharmacy Practice, University of Illinois at Chicago

Reprints: Nancy L Shapiro PharmD BCPS, Department of Pharmacy Practice, University of Illinois at Chicago, 833 S. Wood St. (M/C 886), Chicago, IL 60612-7230, fax 312/996-0379, nlasack{at}uic.edu

OBJECTIVE: To review the literature investigating initial dosing of warfarin at 5 or 10 mg for treatment of acute venous thromboembolism.

DATA SOURCES: Articles were identified through searches of MEDLINE (1966–December 2003) using the key words warfarin, oral anticoagulation, warfarin dose, warfarin initiation, venous thromboembolism, and anticoagulation. Additional references were located through review of the bibliographies of the articles cited.

STUDY SELECTION AND DATA EXTRACTION: Studies of the initial dosing of warfarin at 5 or 10 mg were evaluated and relevant information was included, as were those that identified known factors that influence the maintenance dose of warfarin.

DATA SYNTHESIS: For the treatment of acute venous thromboembolism, warfarin dosing is often provider dependent. Until recently, studies suggested that 5 mg initiation was as effective as 10 mg, without increasing the risk of bleeding. However, the most recent study comparing a 5- versus 10-mg initial dosing nomogram supports an initial dose of 10 mg. These results should be interpreted with caution, however, since patients at high risk for bleeding were excluded from the study. Several patient-specific factors will affect the maintenance dose, guiding clinicians to start with lower (<5 mg) or higher (>5 mg) doses.

CONCLUSIONS: Although recent evidence supports a 10-mg initiation nomogram, clinicians should consider patient-specific factors prior to deciding an initial warfarin dose. If a 10-mg loading dose is utilized, strict compliance with the protocol is necessary.

Key Words: thromboembolic disease, warfarin dosing

Published Online, November 2, 2004. www.theannals.com, DOI 10.1345/aph.1E083

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