A trial to see if two antimalarial drugs could prevent Covid-19 has started in Brighton and Oxford.
Chloroquine, hydroxychloroquine or a placebo will be given to more than 40,000 healthcare professionals from Europe, Africa, Asia and South America.
All participants are staff in contact with Covid-19 patients.
US President Donald Trump was criticized this week after saying he was taking hydroxychloroquine, despite warnings that it could be dangerous.
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The first UK participants in the global trial will be enrolled Thursday at Brighton and Sussex University Hospitals and John Radcliffe Hospital in Oxford.
They will receive hydroxychloroquine or a placebo for three months. At sites in Asia, participants will receive chloroquine or a placebo.
These are the first of 25 sites planned in the UK, with results expected by the end of the year.
The trial is open to anyone providing direct care to patients with coronavirus in the UK, as long as they have not been diagnosed with Covid-19.
It will check whether the drugs can prevent health workers exposed to the virus from contracting it.
“Beneficial or harmful”
One of the study’s leaders, Professor Nicholas White of the University of Oxford, said: “We really don’t know if chloroquine or hydroxychloroquine is beneficial or harmful against Covid-19. “
But, he said, a randomized controlled trial like this, where neither the participant nor the researchers know who was given the drug or a placebo, was the best way to find out.
“A widely available, safe and effective vaccine may be far away,” said Professor Martin Llewelyn of Brighton and Sussex Medical School, who is also leading the study.
“If drugs as well tolerated as chloroquine and hydroxychloroquine could reduce the chances of getting Covid-19, it would be incredibly valuable. “
Drugs can reduce fever and inflammation and are used both as a prevention and as a treatment for malaria.
Hydroxychloroquine regulates the body’s immune response and is also used to treat rheumatoid arthritis and lupus – an inflammatory disease caused by an overactive immune system.
Lupus charities in the UK and the US have expressed concern that demand for the drug associated with the coronavirus could threaten the supply of patients who already depend on it.
The drug caught the eye after US President Donald Trump suggested it might be of benefit, and said this week that he was taking hydroxychloroquine to ward off the coronavirus.
The US Food and Drug Administration has warned against using the drug outside of hospitals, where the agency has granted temporary approval for use in certain cases, or clinical trials.
As the University of Oxford trial takes place in a controlled clinical environment, the World Health Organization has warned that some people are taking self-medication and are at risk of serious injury.
It has not yet been shown to be safe and effective in preventing or treating coronavirus and can cause dangerous cardiac arrhythmias.
The trial also involves researchers from the United Kingdom, Thailand, Vietnam, Laos, Cambodia and Italy.