Antithrombotic Therapy Not Warranted in
COVID-19 Outpatients

Fran Lowry

October 20, 2021

Antithrombotic therapy in clinically stable, nonhospitalized COVID-19 patients does not offer protection against adverse cardiovascular or pulmonary events, new randomized clinical trial results suggest.

Antithrombotic therapy has proven useful in acutely ill inpatients with COVID-19, but in this study, treatment with aspirin or apixaban (Eliquis) did not reduce the rate of all-cause mortality, symptomatic venous or arterial thromboembolism, myocardial infarction, stroke, or hospitalization for cardiovascular or pulmonary causes in patients ill with COVID-19 but who were not hospitalized.

"Among symptomatic, clinically stable outpatients with COVID-19, treatment with aspirin or apixaban compared with placebo did not reduce the rate of a composite clinical outcome," the authors conclude. "However, the study was terminated after enrollment of 9% of participants because of a primary event rate lower than anticipated."

The study, which was led by Jean M. Connors, MD, Brigham and Women's Hospital, Boston, Massachusetts, was published online October 11 in JAMA.

The ACTIV-4B Outpatient Thrombosis Prevention Trial was a randomized, adaptive, double-blind, placebo-controlled trial that sought to compare anticoagulant and antiplatelet therapy among 7000 symptomatic but clinically stable outpatients with COVID-19.

The trial was conducted at 52 sites in the US between September 2020 and June 2021, with final follow-up this past August 5, and involved minimal face-to-face interactions with study participants.

Patients were randomized in a 1:1:1:1 ratio to aspirin (81 mg orally once daily; n = 164 patients), prophylactic-dose apixaban (2.5 mg orally twice daily; n = 165), therapeutic-dose apixaban (5 mg orally twice daily; n = 164), or placebo (n = 164) for 45 days.

The primary endpoint was a composite of all-cause mortality, symptomatic venous or arterial thromboembolism, myocardial infarction, stroke, or hospitalization for cardiovascular or pulmonary cause.

The trial was terminated early this past June by the independent data monitoring committee because of lower than anticipated event rates. At the time, just 657 symptomatic outpatients with COVID-19 had been enrolled.

The median age of the study participants was 54 years (Interquartile Range [IQR] 46-59); 59% were women.

The median time from diagnosis to randomization was 7 days, and the median time from randomization to initiation of study medications was 3 days.

The trial's primary efficacy and safety analyses were restricted to patients who received at least one dose of trial medication, for a final number of 558 patients.

Among these patients, the primary endpoint occurred in 1 patient (0.7%) in the aspirin group, 1 patient (0.7%) in the 2.5 mg apixaban group, 2 patients (1.4%) in the 5-mg apixaban group, and 1 patient (0.7%) in the placebo group.

The researchers found that the absolute risk reductions compared with placebo for the primary outcome were 0.0% (95% CI not calculable) in the aspirin group, 0.7% (95% CI, -2.1% to 4.1%) in the prophylactic-dose apixaban group, and 1.4% (95% CI, -1.5% to 5%) in the therapeutic-dose apixaban group.

No major bleeding events were reported.

The absolute risk differences compared with placebo for clinically relevant nonmajor bleeding events were 2% (95% CI, -2.7% to 6.8%) in the aspirin group, 4.5% (95% CI, -0.7% to 10.2%) in the prophylactic-dose apixaban group, and 6.9% (95% CI, 1.4% to 12.9%) in the therapeutic-dose apixaban group.

Safety and efficacy results were similar in all randomly assigned patients.

The researchers speculated that a combination of two demographic shifts over time may have led to the lower than anticipated rate of events in ACTIV-4B.

"First, the threshold for hospital admission has markedly declined since the beginning of the pandemic, such that hospitalization is no longer limited almost exclusively to those with severe pulmonary distress likely to require mechanical ventilation," they write. "As a result, the severity of illness among individuals with COVID-19 and destined for outpatient care has declined.

"Second, at least within the US where the trial was conducted, individuals currently being infected with SARS-CoV-2 tend to be younger and have fewer comorbidities when compared with individuals with incident infection at the onset of the pandemic," they add.

Further, COVID-19 testing was quite limited early in the pandemic, they note, "and it is possible that the anticipated event rates based on data from registries available at that time were overestimated because the denominator (ie, the number of infected individuals overall) was essentially unknown."

Robust Evidence

"The ACTIV-4B trial is the first randomized trial to generate robust evidence about the effects of antithrombotic therapy in outpatients with COVID-19," Otavio Berwanger, MD, PhD, director of the Academic Research Organization, Hospital Israelita Albert Einstein, Sao Paulo-SP, Brazil, told | Medscape Cardiology.

"It should be noted that this was a well-designed trial with low risk of bias. On the other hand, the main limitation is the low number of events and, consequently, the limited statistical power," said Berwanger, who wrote an accompanying editorial.

The ACTIV-4B trial has immediate implications for clinical practice, he added.

"In this sense, considering the neutral results for major cardiopulmonary outcomes, the use of aspirin or apixaban for the management of outpatients with COVID-19 should not be recommended."

ACTIV-4B also provides useful information for the steering committees of other ongoing trials of antithrombotic therapy for patients with COVID-19 who are not hospitalized, Berwanger added.

"In this sense, probably issues like statistical power, outcome choices, recruitment feasibility, and even futility would need to be revisited. And finally, lessons learned from the implementation of an innovative, pragmatic, and decentralized trial design represent an important legacy for future trials in cardiovascular diseases and other common conditions," he said.

The study was funded by the National Institutes of Health, and the National Heart, Lung, and Blood Institute. Connors reports financial relationships with Bristol-Myers Squibb, Pfizer, Abbott, Alnylam, Takeda, Roche, and Sanofi. Berwanger reports financial relationships with AstraZeneca, Amgen, Servier, Bristol-Myers Squibb, Bayer, Novartis, Pfizer, and Boehringer Ingelheim.

JAMA. Published online October 11, 2021. Abstract, Editorial

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