It is one of a number of drugs being tested in the UK’s Randomised Evaluation of Covid-19 Therapy (Recovery) trial – the world’s largest randomised clinical trial of potential coronavirus treatments.
Recovery, which is being co-ordinated at Oxford University, signed up 1,000 patients from 132 different hospitals in its first 15 days and is now reported to have nearly 3,000 volunteers.
Hydroxychlorquine has been hailed as a game-changer by the US president, despite his top adviser Dr Anthony Fauci warning against widespread use of it as an untested treatment for Covid-19.
“Take it. What do you have to lose?” Mr Trump told Americans on Saturday, prompting warnings from leading cardiac organisations that the drug can dangerously disrupt heart rhythms in some patients.
Two small studies, without proper control groups, in China and France – the latter now discredited – have suggested the drug may help coronavirus patients.
Laboratory research has also suggested the drug may stop some coronaviruses and influenza entering cultured cells, although trials on human influenza patients showed no such effect.
The drug – created 75 years ago – has also been used to treat lupus and rheumatoid arthritis, and its ability to calm overactive immune systems has boosted hopes it may help counter Covid-19, which can cause the body's infection response to go into a state of dangerous overdrive, known as a cytokine storm.
One of Exeter’s first Covid-19 patients to take part in the Recovery trial says there is still no way of knowing whether or not her recovery was aided by Hydroxychloroquine.
Claire Fuller, 56, was taken into RD&E on 31 March, when her breathing deteriorated 10 days after developing a dry cough. “It was really scary how it just suddenly turned,” she said.
The mother of two, from Tiverton, Devon, was asked to take part in the study while in A&E. “It didn’t take long for me to agree," she said. "The more people they get, the better.”
Ms Fuller said she was given a loading dose of eight tablets of hydroxychloroquine to start with and then, after another heavy loading dose, it was two tablets for the remaining four days she was on the Covid-19 ward.
She said that she has no idea whether some of the symptoms she experienced, and her recovery, were due to the infection or were side-effects of the drug.
“I was getting what was like a flushing feeling – a hot, sharp, tingling going through my lungs," she said. “I don’t know whether this was me responding to the drug or the virus.
“Until they get more people through the trial they will not know. That’s the point of the study.”
Ms Fuller said the only other possible side-effect she suffered was some gastric issues. But she thinks this may have been virus rather than drug-related as another patient in her four-bed Covid-19 bay had the same and was not on the trial.
She added: “I think, though, that if I’d had a bad reaction to the drug, that would have been evidenced.”
Ms Fuller said the doctors, like their patients, are not sure which presentations are down to the virus or the drugs.
“The doctors were saying that all the patients coming in with Covid-19 are coming in with a slightly different presentation," she said. "They are literally learning with each one being admitted, poor guys.”
Ms Fuller, who works as a global manager for a veterinary company, is now recovering at home after she was discharged a week ago. While she does not know if the drug aided her recovery, she encouraged anyone who has the chance to sign up for the trial.
Recovery is also trialling three other drugs. These are HIV drug lopinavir-ritonavir, the steroid dexamethasone, and the commonly-used antibiotic azithromycin.
It is is one of three key national trials in the UK. The others are Principle, which is focused on higher risk patients in primary care, and Remap-Cap, which is concentrated on critically ill patients with community-acquired pneumonia.
“There is an urgent need for reliable evidence on the best care for patients with Covid-19," said Peter Horby at the outset of the trial, for which he is chief investigator.
“Providing possible new treatments through a well-designed clinical trial is the best way to get that evidence.”
The University of Oxford professor of emerging infectious diseases and global health added: “All patients will receive the standard full medical care, regardless of which treatment group they are placed in.”
Additional reporting by PA
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies