Enoxaparin versus Placebo to Prevent Symptomatic Venous Thromboembolism in Hospitalized Older Adult Medical Patients

BACKGROUND: Admission to the hospital is a major risk factor for the development of venous thromboembolism (VTE). Whether thromboprophylaxis with low-molecular-weight heparin prevents symptomatic VTE in medically ill, hospitalized older adults remains debated. METHODS: In a prospective, randomized, placebo-controlled, double-blind, multicenter trial, older adults (>70 years of age) hospitalized for acute medical conditions were randomly assigned to receive 40 mg a day of low-molecular-weight heparin (enoxaparin) or placebo for 6 to 14 days. The primary efficacy outcome was the cumulative incidence of symptomatic VTE (distal or proximal deep vein thrombosis, fatal or nonfatal pulmonary embolism) at 30 days. The primary safety outcome was major bleeding. Secondary outcomes included efficacy and safety outcomes at 90 days. RESULTS: The trial was prematurely discontinued in September 2020, 5 years after enrollment began, because of drug supply issues. By the time of trial discontinuation, 2559 patients had been randomly assigned at 47 centers. Median age was 82 years and 60% of patients were female. In the intention-to-treat population, the primary efficacy outcome occurred in 22 out of 1278 (cumulative incidence, 1.8%) patients in the enoxaparin group and in 27 out of 1263 (cumulative incidence, 2.2%) patients in the placebo group (cumulative incidence difference, −0.4 percentage points; 95% confidence interval, −1.5 to 0.7), with no significant difference in time to VTE (P=0.46). The incidence of major bleeding was 0.9% in the enoxaparin group and 1.0% in the placebo group. At 90 days there were 14 symptomatic pulmonary emboli in the enoxaparin group and 25 in the placebo group; all 39 pulmonary embolism events resulted in hospital readmission and/or death, with 5 deaths from pulmonary embolism in the enoxaparin group and 11 deaths in the placebo group. CONCLUSIONS: This trial of thromboprophylaxis in medically ill, hospitalized older adults did not demonstrate that enoxaparin reduced the risk of symptomatic VTE after 1 month. Because the trial was prematurely discontinued, larger trials are needed to definitively address this question. (Funded by the French Ministry of Health Programme Hospitalier de Recherche Clinique, grant number PHRC-N-13-0283; ClinicalTrials.gov number, NCT02379806.)