Why Not To Use Warfarin for VTE Treatment in Oncology Patients?

by Amy Smith (as part of her Green Oncology series)

Ever wonder why warfarin is not the anticoagulant of choice for oncology patients?

The CLOT trial studied patients with active cancer with a recent diagnosis of a symptomatic proximal DVT and/or PE.  These patients were treated with dalteparin or warfarin (dosed to an INR of 2-3) for 6 months.  The study found that patients treated with warfarin were more likely to experienced a DVT and/or PE compared to those treated with dalteparin.  Safety data between the two drugs proved to be similar as well with no difference in the occurrence of bleeds or death.

Interested in more details? See below the PICO and citation below.

Patient Population

Adult patients with active cancer and recently diagnosed symptomatic proximal DVT and/or PE.


Dalteparin 200 IU/ kg subcutaneously x 1 month then 150 IU/kg subcutaneously x 5 months (for a total of 6 months).  Dose capped at 18,000 IU. 


Vitamin K antagonist (dosed to an INR of 2-3) x 6 months (bridging with low molecular weight heparin provided)


Primary endpoint:

Recurrence of symptomatic proximal DVT and/or PE – HR 0.48 (95% confidence interval 0.33-0.77; P=0.002)

Secondary endpoint:

Clinically overt bleeding and death – Not statistically significant

Lee, A.Y.Y et al.  Low-Molecular-Weight Heparin versus a Coumarin for the Prevention of Recurrent Venous Thromboembolism in Patients with Cancer.  N Engl J Med 2003; 349:146-153


Figure from CancerThrombosis.org (click here for full article)


Amy Smith is a graduate of the College of Pharmacy at the University of Saskatchewan.  After completing a hospital residency program with the Regina Qu’Appelle Health Region, Amy began working with the Saskatchewan Cancer Agency in Saskatoon as a pediatric oncology pharmacist.  She is now attending the U of T post-baccalaureate PharmD program . During her time away from work, Amy enjoys traveling, volunteering and participating in a various athletics including powerlifting and running. Amy is a member of CAPhO's Communication Committee. 

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