Medicine by the Numbers

October 9, 2009


Chris Tully MD

Faculty peer reviewed

What is the number of patients needed to prophylax to prevent an episode of venous thromboembolism in a hospitalized medical patient?


 The use of prophylactic anticoagulation for venous thromboembolism (VTE) is considered standard of care in the inpatient medical setting in order to prevent deep venous thrombosis (DVT) and fatal and nonfatal pulmonary embolism (PE). While a majority of the knowledge stems of post-surgical patients, there has been an increasing volume of research emphasizing and illustrating the benefit in hospitalized medical patients. Three randomized controlled trials examined this question of anticoagulation with three different pharmacologic treatments, enoxaparin, dalteparin (LMWHs) and fondaparinux (inhibitor activated factor X). In each case there was a significant reduction in the incident of VTE. See results below:

Intervention (vs. placebo) Absolute Risk Reduction (ARR) Number needed to treat (NNT) P value Relative Risk Reduction (RRR)
Enoxaparin 40mg daily 9.4% 11 <0.001 63%
Dalteparin 5000U daily 2.2% 45 =0.002 44%
Fonadparinux 2.5mg daily 4.9% 21 =0.03 47%

Another common choice in the prevention of VTE is the use of unfractionated heparin (UFH) given the high cost of treatment associated with LMWHs or factor Xs inhibitors. A meta-analysis comparing UFH and LMWH showed no significant difference in DVT, PE or death between the two interventions. While there was a statistically significant decreased risk of major bleed with LMWH in this meta-analysis, the ARR was 0.0076%, and therefore the NNT with LMWH to prevent one major bleed would be 13,157 patients, meaning that UFH is still a safe and appropriate solution.

Either way, in hospitalized patients, prophylactic anticoagulation is a critical and important element of appropriate patient care.

Faculty peer Reviewed by Kelly Crotty MD, NYU Division of General Internal Medicine

Francis C. Prophylaxix for Thromboembolism in Hospitalized Medical Patients. N Engl J Med 356:1438, April 5, 2007

Mismetti P, Laporte-Simitsidis S, Tardy B, et al. Prevention of venous thromboembolism in internal medicine with unfractionated or low molecular weight heparins: a meta-analysis of randomised clinical trials. Thromb Haemost 2000:83: 14-9.

2 comments on “Medicine by the Numbers

  • Avatar of John K. Mackenzie
  • Avatar of robert maslansky md
    robert maslansky md on

    Just got home from a five day non-surgical stint(not ‘stent’) on the 17th floor.Not having practiced in-patient medicine for a number of years; BOY have things changed. I was given enoxaparin every night. Big change! Nurses unfailingly pleasant and helpful . . . bigger change! Food, well…ugh. No change.

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