Many people who are hospitalized with COVID-19 have excessive blood clotting, which can be fatal.
A pilot study of hospitalized patients suggests that a low dose of the anticoagulant aspirin could reduce the need for mechanical ventilation and admission to intensive care, as well as the risk of dying.
A larger clinical study will be necessary to confirm the findings.
Early in the pandemic, research showed that almost one-third of people with COVID-19 in intensive care experienced potentially fatal complications as a result of excessive blood clotting.
Another study found that many of these patients had unusually “sticky” blood that tended to coagulate easily.
“As we learned about the connection between blood clots and COVID-19, we knew that aspirin — used to prevent stroke and heart attack — could be important for COVID-19 patients,” says Jonathan Chow, M.D., assistant professor of anesthesiology and critical care medicine at the George Washington University School of Medicine and Health Sciences in Washington, D.C.
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By “thinning” the blood, aspirin helps prevent the formation of clots, or thrombi, that can block the blood vessels supplying the heart, brain, lungs, and other vital organs.
One widely recognized limitation of aspirin as a preventive treatment is that it leads to a small increase in the risk of bleeding.
Given the low cost of aspirin and the evidence of its overall safety and efficacy in cardiovascular disease, however, Dr. Chow and his colleagues decided to conduct a pilot study of hospitalized patients with COVID-19.
Their analysis suggests that a low dose of aspirin shortly before or after hospital admission is associated with a significantly reduced risk of mechanical ventilation, admission to intensive care, and in-hospital mortality.
At the same time, the researchers found no evidence that aspirin increased the risk of bleeding.
“Aspirin is low cost, easily accessible, and millions are already using it to treat their health conditions,” says Dr. Chow. “Finding this association is a huge win for those looking to reduce risk from some of the most devastating effects of COVID-19.”
In addition to preventing clotting, aspirin reduces levels of an immune signaling molecule or cytokine called interleukin-6 (IL-6) in the blood. The molecule is associated with the immune overreaction, or “cytokine storm,” that can affect people with COVID-19 in intensive care.
The authors emphasize that other researchers will need to conduct randomized controlled clinical trials to confirm their findings.
Their retrospective study analyzed the records of 412 adults with COVID-19 who were admitted to one of several hospitals in the United States between March 2020 and July 2020.
Of these people, 98 took aspirin in the week before admission or during the first 24 hours after admission. The researchers compared the outcomes for these individuals with those for the 314 people who did not take aspirin.
Among those taking aspirin, the median daily dose was 81 milligrams, and the median length of treatment was 6 days.
In their analysis of the data, the researchers accounted for other variables that scientists have shown to affect the severity of COVID-19, including age, sex, body mass index, race, hypertension, and diabetes.
After these adjustments, aspirin use was associated with a 43% reduced risk of intensive care unit admission, a 44% reduced risk of mechanical ventilation, and a 47% reduced risk of dying in the hospital.
While there was no evidence that aspirin increased the risk of bleeding, the authors recommend caution:
“Until a randomized controlled trial of aspirin is performed, it is imperative to exercise cautious optimism and deliberately balance aspirin’s known risks against its potential benefits in patients afflicted by COVID-19.”
Interestingly, the researchers found no difference in overt thrombosis between the aspirin and non-aspirin groups. Overt thrombosis is the term for large blood clots that show up in standard diagnostic images.
However, they point out that the number of cases of thrombosis in the two groups was low, which limits the statistical reliability of this finding.
In addition, they note that small blood clots, called microthrombi, are difficult to spot without the use of more specialist, nonstandard imaging techniques.
The researchers acknowledge that their sample size was modest and that the study was observational, meaning that it could not prove that aspirin reduced the severity of COVID-19 in hospitalized patients.
The people who took aspirin may have received different medical treatments due to their underlying conditions, for example, which would skew the results.
The researchers were also unable to account for other medications that people may have been taking that could increase their risk of blood clots, such as birth control pills and hormone replacement therapy (HRT).