The EFFORT trial: Preoperative enoxaparin versus postoperative fondaparinux for thromboprophylaxis in bariatric surgical patients: a randomized double-blind pilot trial

Surg Obes Relat Dis. 2015 May-Jun;11(3):672-83. doi: 10.1016/j.soard.2014.10.003. Epub 2014 Oct 23.


Background: Prophylaxis for venous thromboembolism is routinely performed for all patients undergoing bariatric surgery. However, there is disagreement regarding the optimal dosing and duration of anticoagulant therapy. Furthermore, there is little data regarding the incidence of asymptomatic deep venous thrombosis (DVT) in this population. Our objective was to conduct a pilot randomized double blind study to evaluate the pharmacodynamic parameters of 2 different anticoagulation medications (enoxaparin and fondaparinux) administered to patients undergoing bariatric surgery.

Methods: From July 2010 to August 2013, 198 consecutive bariatric surgery patients from an academic institution were randomized in a double blinded manner to receive either 40 mg enoxaparin twice daily or 5mg fondaparinux sodium once daily. Antifactor Xa activity was measured on all patients in both study arms, 3 hours after the first dose (on the day of the operation), immediately before the second dose (postoperative day one), and 3 hours after the second dose. At the routine 2 week postoperative visit, patients underwent magnetic resonance venography (MRV) to detect DVT. The primary outcome was attainment of therapeutic antifactor Xa levels. The secondary outcome was DVT, as detected by MRV. Safety outcomes were perioperative bleeding, perioperative complications, and death.

Results: Of 198 patients randomized, 177 underwent MRV and 137 had interpretable antifactor Xa levels. Nearly half of the patients (47.4%) did not attain target prophylactic antifactor Xa levels. Adequate antifactor Xa levels were more common with fondaparinux (74.2%) than with enoxaparin (32.4%). Antifactor Xa levels were also associated with preoperative D-dimer level. 4 of the 175 patients who underwent MRV developed DVT, 2 in each arm of the study. No major adverse events occurred in either arm.

Conclusion: Fondaparinux was much more likely to produce target prophylactic antifactor Xa levels than enoxaparin. Both regimens appear to be equally effective at reducing the risk of DVT. Further prospective studies are needed to determine the optimal DVT prophylaxis regimen in the bariatric surgical population.

Keywords: Anticoagulation; Bariatric surgery; Clinical trial; Prophylaxis; Venous thromboembolism.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Anticoagulants / administration & dosage
  • Bariatric Surgery / adverse effects*
  • Dose-Response Relationship, Drug
  • Double-Blind Method
  • Enoxaparin / administration & dosage*
  • Female
  • Follow-Up Studies
  • Fondaparinux
  • Humans
  • Male
  • Middle Aged
  • Obesity, Morbid / surgery*
  • Pilot Projects
  • Polysaccharides / administration & dosage*
  • Postoperative Care / methods*
  • Postoperative Complications
  • Preoperative Care / methods*
  • Prospective Studies
  • Treatment Outcome
  • Venous Thromboembolism / etiology
  • Venous Thromboembolism / prevention & control*
  • Young Adult


  • Anticoagulants
  • Enoxaparin
  • Polysaccharides
  • Fondaparinux