Just over one in four patients who received the anti-malaria drug died within 28 days of starting treatment, while slightly less than one in four of those who received usual care -- basically supportive management of heart and lung symptoms -- died within that time frame, researchers heading up the RECOVERY trial said.
The findings are based on an analysis of data from 80 percent of the study participants, they said.
"These data convincingly rule out any meaningful mortality benefit of hydroxychloroquine in patients hospitalized with COVID-19," they said in a statement. "Full results will be made available as soon as possible," they said.
"There has been huge speculation and uncertainty about the role of hydroxychloroquine as a treatment for COVID-19, but an absence of reliable information from large randomized trials," Dr. Martin Landray, one the principle investigators, said in a statement.
The announcement of the findings comes just one day after the authors of two studies published in the Lancet and the New England Journal of Medicine chose to retract their published research due to alleged issues with the data source.
The two retracted studies had also concluded that hydroxychloroquine offered "no clinical benefit" in patients infected with the new coronavirus, SARS-CoV-2. They also linked the drug with significant heart-related side effects.
"Today's preliminary results from the RECOVERY Trial are quite clear -- hydroxychloroquine does not reduce the risk of death among hospitalized patients with this new disease," said Landray, who is a professor of medicine and epidemiology at the University of Oxford's Nuffield Department of Population Health. "This result should change medical practice worldwide."
Launched in March, the RECOVERY trial is designed to test a range of potential treatments for COVID-19, including hydroxycholoroquine, the HIV regimen lopinavir-ritonavir, the steroid dexamethasone, the antibiotic azithromycin, the injectable anti-inflammatory tocilizumab and convalescent blood plasma.
Convalescent plasma is collected from donors who have recovered from COVID-19, and is believed to contain antibodies against SARS-CoV-2 virus.
To date, more than 11,000 patients from 175 National Health Service hospitals in Britain have been enrolled. The independent Data Monitoring Committee reviewed the emerging data every two weeks to determine if there is evidence that would be strong enough to affect national and global treatment of COVID-19.
On Thursday, the committee recommended that the chief investigators review the unblinded data on the hydroxychloroquine arm of the trial, which compared 1,542 patients treated with hydroxychloroquine with 3,132 patients who received usual care.
The investigators found that there was no significant difference in 28-day mortality between those treated with hydroxychloroquine -- 25.7 percent -- and those who received usual care -- 23.5 percent. The drug did not have any "beneficial effects on hospital stay duration or other outcomes," the researchers said.
Based on these findings, the researchers said in a statement, "we have therefore decided to stop enrolling participants to the hydroxychloroquine arm of the RECOVERY Trial with immediate effect."