The drug hydroxychloroquine offers no benefit to patients hospitalised with Covid-19, according to a new study in The Lancet.
Experts found that hydroxychloroquine – and a related medicine chloroquine – was linked to an increased risk of death and heart arrhythmias among people severely ill in hospital with coronavirus.
US President Donald Trump has been criticised after he said he had nothing to lose by taking hydroxychloroquine, which is used to treat malaria and arthritis, despite warnings it could be unsafe.
The authors of the new study said neither drug should be used to treat Covid-19 outside of clinical trials and said randomised clinical trials were needed.
Earlier this week it was announced that a trial to see whether the drugs could prevent Covid-19 had begun in Brighton and Oxford.
Chloroquine, hydroxychloroquine or a placebo will be given to more than 40,000 healthcare workers from Europe, Africa, Asia and South America.
The Lancet study analysed data from almost 15,000 patients with Covid-19 receiving the drugs and 81,000 people who did not.
Treatment with the medications among patients with Covid-19, either alone or in combination with antibiotics, was linked to an increased risk of serious heart rhythm complications and death.
But the authors stressed that anyone taking these drugs for other conditions should not stop taking them as the trial looked specifically at Covid-19.
Professor Mandeep Mehra, lead author of the study and executive director of the Brigham and Women’s Hospital Centre for Advanced Heart Disease in Boston in the US, said: “This is the first large scale study to find statistically robust evidence that treatment with chloroquine or hydroxychloroquine does not benefit patients with Covid-19.
“Instead, our findings suggest it may be associated with an increased risk of serious heart problems and increased risk of death.
“Randomised clinical trials are essential to confirm any harms or benefits associated with these agents.
“In the meantime, we suggest these drugs should not be used as treatments for Covid-19 outside of clinical trials.”
The researchers estimated that the excess risk attributable to the use of the drugs rather than other factors such as underlying health issues ranged from 34% to 45%.
Dr Stephen Griffin, associate professor in the school of medicine at the University of Leeds, called for more research but said: “This is potentially a landmark study for Covid-19 therapy.
“Whilst not a placebo controlled trial, an observational study on this scale undertaken with stringent and meticulous analysis is powerful indeed.
“The key finding of this study is that neither single, nor combination therapy with either chloroquine or hydroxychloroquine appear to provide any patient benefit in large numbers of Covid-19 infected patients.
“Moreover, and worryingly, such therapy actually may be harmful as treatment was associated with cardiovascular problems relating to heart rhythm.”
Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, said more research was needed, but added: “A definitive answer still awaits the results of the randomised trials, but it is clear that the drugs should not be given for treatment of Covid-19 other than in the context of a randomised trial.
“It might even be said that to go on giving them other than in a trial is unethical, given this evidence that is not yet contradicted by other available evidence.”