A new study aims to establish whether hydroxychloroquine can prevent Covid-19 for staff in Brighton and Oxford, with the study opening from Thursday.
The investigation will be led by the Bangkok-based Mahidol Oxford Tropical Medicine Research Unit (MORU), which is supported by the University of Oxford and charity Wellcome.
More than 40,000 people who work with confirmed or suspected coronavirus patients from Europe, Africa, Asia and South America will take part in the randomised trial.
There is no concrete evidence to suggest that hydroxychloroquine can combat or prevent Covid-19, but it can cause significant side effects - such as an irregular heartbeat - in some patients.
MORU co-principal investigator Professor Sir Nicholas White said: "We really do not know if chloroquine or hydroxychloroquine are beneficial or harmful against Covid-19.
“The best way to find out if they are effective in preventing Covid-19 is in a randomised clinical trial.”
Earlier this week, Mr Trump admitted he had been taking the drug, despite there being little evidence to suggest it is effective.
Dr Stephen Griffin, associate professor in the school of medicine at the University of Leeds, also said those that follow Mr Trump’s example might not only endanger themselves, “but could also deprive patients with chronic autoimmune conditions of their much-needed medication”.
Scientists say the drug has some “very serious” side-effects and there is no evidence that it prevents or treats the disease.
But those running the MORU trial have said chloroquine and hydroxychloroquine “could reduce the chances” of catching coronavirus amid fears of a second wave of infections.
The study’s lead UK investigator, Prof Martin Llewelyn of Brighton and Sussex School, said a “safe and effective vaccine may be a long way off”.
He added: “If drugs as well tolerated as chloroquine and hydroxychloroquine could reduce the chances of catching Covid-19 this would be incredibly valuable.”
The UK Government has said that chloroquine and hydroxychloroquine are not licensed to treat Covid-19 related symptoms or prevent infection.
It said the drugs should not be used outside ongoing clinical trials which have reached no conclusions over the safety and effectiveness of the medicine on coronavirus.
The first UK participants in the new trial can be enrolled at Brighton and Sussex University Hospitals and at Oxford’s John Radcliffe Hospital.
Further testing is expected at another four sites by the end of May, with 25 total locations opened across the UK before July and more planned around the globe.
The team aims to deliver results by the end of 2020.
Previous studies do not suggest hydroxychloroquine is beneficial in the fight against Covid-19.
The US's Food and Drug Administration has said hydroxychloroquine should only be used for coronavirus in formal studies.
Two large observational studies, each involving around 1,400 patients in New York, recently found no benefit from hydroxychloroquine.
Two new ones published on Thursday in the medical journal BMJ reached the same conclusion.
One, by French researchers, gave 84 hospital patients the drug and 97 others the usual care.
There were no differences in the odds of death, need for intensive care or developing severe illness.
The other study from China was a stricter test: 150 adults in hospital with mild or moderate illness were randomly assigned to receive hydroxychloroquine or usual care.
The drug made no difference in rates of clearing the virus or time to relief of symptoms, and they brought more side effects.
In April, the National Institutes of Health launched a study testing hydroxychloroquine versus a placebo drug in 500 Covid-19 patients.
Last week, NIH announced another study to see if hydroxychloroquine plus azithromycin can prevent hospital admission or death in people with mild to moderate illness.
About 2,000 US adults with confirmed coronavirus infections and symptoms such as fever, cough or shortness of breath will receive the drugs or placebo pills.
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