Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Cochrane is preparing a series of rapid reviews to help decision makers with their response to COVID-19. In October 2020, we published the findings on the effects of anticoagulants and lead author, Ronald Flumignan from the Federal University of Sao Paulo in Brazil describes what they found in this podcast.

Ronald: COVID-19 typically affects a person’s lungs and airways, but, as well as these breathing problems, about one in six people who go into hospital with COVID-19 may develop blood clots in their veins or arteries. Anticoagulants prevent these clots from forming but they can cause unwanted effects such as bleeding. Some guidelines recommend giving these medicines when people are first admitted to hospital with COVID-19, to prevent blood clots from developing, rather than waiting to see if blood clots develop and then treating them with anticoagulants. We wanted to know whether using this prophylactic or preventative approach of giving anticoagulants when people are hospitalised with COVID-19 reduced the number of deaths. We also wanted to know whether these people needed less support with breathing, still developed harmful blood clots, or experienced bleeding or any other unwanted events such as nausea, vomiting, kidney problems or the need for amputation.
We hoped to find randomised trials testing the use of anticoagulants against usual care or placebo because they give the best evidence, but no such studies are available at this time. So, instead, we relied on seven non‐randomised ‘retrospective’ studies that looked back at treatment given to a total of nearly 6000 people. These studies took place in intensive care units, hospital wards and emergency departments in China, Italy, Spain and the USA. They provided evidence on deaths and bleeding but no evidence on respiratory support, blood clotting or other unwanted effects. The large differences between the studies also meant that we were not able to pool their results.
Six studies, with nearly 5700 participants, compared patients who had, or had not been given anticoagulants. One of these studies reported a reduction in mortality with anticoagulants and another study found a reduction in mortality in severely ill people; but three studies reported no effect on mortality and the sixth reported no deaths in either group. One of these studies reported major bleeding in 3% of participants who received anticoagulants and in 1.9% of those who did not receive the drugs.
The seventh study in our review compared a treatment dose with a preventive dose of anticoagulants. All 244 participants in this study were in the intensive care unit on mechanical ventilators. They may or may not have had blood clots but were given either an anticoagulant at a higher dose usually used to treat clots or a lower dose used to prevent clots. The study found that about a third of people who received the treatment dose died, compared to more than half with the preventive dose. It also found that major bleeding was more common in participants who received the treatment dose, at about 32% compared with 21% of those who received the lower, preventive dose.
In summary, at the moment, we do not know whether anticoagulants are a useful preventive treatment for people with COVID-19, because of the high uncertainty about the current evidence. On the positive side, we know of at least 22 ongoing studies, including 20 randomised trials with around 15,000 participants and we will add the results of these studies to our review when they are available. These better quality studies should then help us to provide a conclusive answer on this important topic.

Monaz: To find out more about the current research evidence and to watch for updates as the trial results become available, you can access the review online. Just visit Cochrane Library dot com and search 'anticoagulants and COVID-19'.