Effect of Thromboprophylaxis on Clinical Outcomes After COVID-19 Hospitalization

ACTIV-4C Study Group

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


BACKGROUND: Patients hospitalized with COVID-19 have an increased incidence of thromboembolism. The role of extended thromboprophylaxis after hospital discharge is unclear.

OBJECTIVE: To determine whether anticoagulation is superior to placebo in reducing death and thromboembolic complications among patients discharged after COVID-19 hospitalization.

DESIGN: Prospective, randomized, double-blind, placebo-controlled clinical trial. (ClinicalTrials.gov: NCT04650087).

SETTING: Done during 2021 to 2022 among 127 U.S. hospitals.

PARTICIPANTS: Adults aged 18 years or older hospitalized with COVID-19 for 48 hours or more and ready for discharge, excluding those with a requirement for, or contraindication to, anticoagulation.

INTERVENTION: 2.5 mg of apixaban versus placebo twice daily for 30 days.

MEASUREMENTS: The primary efficacy end point was a 30-day composite of death, arterial thromboembolism, and venous thromboembolism. The primary safety end points were 30-day major bleeding and clinically relevant nonmajor bleeding.

RESULTS: Enrollment was terminated early, after 1217 participants were randomly assigned, because of a lower than anticipated event rate and a declining rate of COVID-19 hospitalizations. Median age was 54 years, 50.4% were women, 26.5% were Black, and 16.7% were Hispanic; 30.7% had a World Health Organization severity score of 5 or greater, and 11.0% had an International Medical Prevention Registry on Venous Thromboembolism risk prediction score of greater than 4. Incidence of the primary end point was 2.13% (95% CI, 1.14 to 3.62) in the apixaban group and 2.31% (CI, 1.27 to 3.84) in the placebo group. Major bleeding occurred in 2 (0.4%) and 1 (0.2%) and clinically relevant nonmajor bleeding occurred in 3 (0.6%) and 6 (1.1%) apixaban-treated and placebo-treated participants, respectively. By day 30, thirty-six (3.0%) participants were lost to follow-up, and 8.5% of apixaban and 11.9% of placebo participants permanently discontinued the study drug treatment.

LIMITATIONS: The introduction of SARS-CoV-2 vaccines decreased the risk for hospitalization and death. Study enrollment spanned the peaks of the Delta and Omicron variants in the United States, which influenced illness severity.

CONCLUSION: The incidence of death or thromboembolism was low in this cohort of patients discharged after hospitalization with COVID-19. Because of early enrollment termination, the results were imprecise and the study was inconclusive.

PRIMARY FUNDING SOURCE: National Institutes of Health.

Original languageEnglish (US)
Pages (from-to)515-523
Number of pages9
JournalAnnals of Internal Medicine
Issue number4
StatePublished - Apr 2023


  • Adult
  • Female
  • Humans
  • Male
  • Middle Aged
  • Anticoagulants/adverse effects
  • COVID-19/prevention & control
  • COVID-19 Vaccines/adverse effects
  • Double-Blind Method
  • Hemorrhage/chemically induced
  • Hospitalization
  • Prospective Studies
  • SARS-CoV-2
  • Treatment Outcome
  • Venous Thromboembolism/drug therapy

ASJC Scopus subject areas

  • Internal Medicine


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