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Original Investigation
January 14, 2020

Effect of Osocimab in Preventing Venous Thromboembolism Among Patients Undergoing Knee Arthroplasty: The FOXTROT Randomized Clinical Trial

Author Affiliations
  • 1Department of Medicine and Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton Ontario, Canada
  • 2Thrombosis and Atherosclerosis Research Institute, Hamilton, Ontario, Canada
  • 3Center for Thrombosis and Hemostasis, University Medical Center Mainz, Mainz, Germany
  • 4Department of Vascular Medicine, Klinikum Darmstadt GmbH, Darmstadt, Germany
  • 5Bayer Pharmaceuticals, Leverkusen, Germany
  • 6Department of Orthopedics, Spine Section, Zealand University Hospital, Koege, Denmark
  • 7University of Oklahoma Health Sciences Center, Hudson College of Public Health, Oklahoma City
JAMA. 2020;323(2):130-139. doi:10.1001/jama.2019.20687
Key Points

Question  Is osocimab, a monoclonal antibody against factor XIa, noninferior to enoxaparin for thromboprophylaxis after knee arthroplasty?

Findings  In this phase 2, noninferiority trial that randomized 813 patients undergoing knee arthroplasty, venous thromboembolism (determined by bilateral venography and symptomatic events) at 10 to 13 days postoperatively occurred in 23.7% of patients receiving 0.3 mg/kg, 15.7% receiving 0.6 mg/kg, 16.5% receiving 1.2 mg/kg, and 17.9% receiving 1.8 mg/kg of osocimab postoperatively; 29.9% receiving 0.3 mg/kg and 11.3% receiving 1.8 mg/kg osocimab preoperatively; and 26.3% receiving enoxaparin and 14.5% receiving apixaban. Given postoperatively, 0.6 mg/kg, 1.2 mg/kg, and 1.8 mg/kg doses of osocimab met criteria for noninferiority compared with enoxaparin at the prespecified noninferiority margin of 5%. Preoperative osocimab 1.8 mg/kg met criteria for superiority compared with enoxaparin.

Meaning  Further studies are needed to establish efficacy and safety of osocimab relative to standard therapies for venous thromboprophylaxis.

Abstract

Importance  The efficacy of factor XIa inhibition for thromboprophylaxis is unknown. Osocimab is a long-acting, fully human monoclonal antibody that inhibits factor XIa.

Objective  To compare different doses of osocimab with enoxaparin and apixaban for thromboprophylaxis in patients who have undergone knee arthroplasty.

Design, Setting, and Participants  Randomized, open-label, adjudicator-blinded, phase 2 noninferiority trial with observer blinding for osocimab doses, conducted at 54 hospitals in 13 countries. Adult patients undergoing unilateral knee arthroplasty were randomized from October 2017 through August 2018 and followed up until January 2019.

Interventions  Single intravenous osocimab postoperative doses of 0.3 mg/kg (n = 107), 0.6 mg/kg (n = 65), 1.2 mg/kg (n = 108), or 1.8 mg/kg (n = 106); preoperative doses of 0.3 mg/kg (n = 109) or 1.8 mg/kg (n = 108); or 40 mg of subcutaneous enoxaparin once daily (n = 105) or 2.5 mg of oral apixaban twice daily (n = 105) for at least 10 days or until venography.

Main Outcomes and Measures  The primary outcome was venous thromboembolism incidence between 10 and 13 days postoperatively (assessed by mandatory bilateral venography performed 10 to 13 days after surgery or confirmed symptomatic deep vein thrombosis or pulmonary embolism). A 5% noninferiority margin compared with enoxaparin was chosen. The primary safety outcome of major or clinically relevant nonmajor bleeding was assessed until 10 to 13 days postoperatively.

Results  Of 813 randomized participants (mean [SD] age, 66.5 years [8.2 years]; body mass index, 32.7 [5.7]; and 74.2% women), 600 were included in the per-protocol population used for the primary analysis. The primary outcome occurred in 18 patients (23.7%) receiving 0.3 mg/kg, 8 (15.7%) receiving 0.6 mg/kg, 13 (16.5%) receiving 1.2 mg/kg, and 14 (17.9%) receiving 1.8 mg/kg of osocimab postoperatively; 23 (29.9%) receiving 0.3 mg/kg and 9 (11.3%) receiving 1.8 mg/kg of osocimab preoperatively; 20 (26.3%) receiving enoxaparin; and 12 (14.5%) receiving apixaban. Osocimab given postoperatively met criteria for noninferiority compared with enoxaparin with risk differences (1-sided 95% CIs) of 10.6% (95% CI, –1.2% to ∞) at the 0.6-mg/kg dose; 9.9% (95% CI, –0.9% to ∞) at the 1.2-mg/kg dose, and 8.4% (95% CI, –2.6 to ∞) at the 1.8-mg/kg dose. The preoperative dose of 1.8 mg/kg of osocimab met criteria for superiority compared with enoxaparin with a risk difference of 15.1%; 2-sided 90% CI, 4.9% to 25.2%). Postoperative and preoperative doses of 0.3 mg/kg of osocimab did not meet the prespecified criteria for noninferiority, with risk differences (1-sided 95% CIs) of 2.6% (95% CI, –8.9% to ∞) and –3.6% (95% CI, –15.5% to ∞), respectively. Major or clinically relevant nonmajor bleeding was observed in up to 4.7% of those receiving osocimab, 5.9% receiving enoxaparin, and 2% receiving apixaban.

Conclusions and Relevance  Among patients undergoing knee arthroplasty, postoperative osocimab 0.6 mg/kg, 1.2 mg/kg, and 1.8 mg/kg met criteria for noninferiority compared with enoxaparin, and the preoperative 1.8-mg/kg dose of osocimab met criteria for superiority compared with enoxaparin for the primary outcome of incidence of venous thromboembolism at 10 to 13 days postoperatively. Further studies are needed to establish efficacy and safety of osocimab relative to standard thromboprophylaxis.

Trial Registration  ClinicalTrials.gov Identifier: NCT03276143

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