While previous observational studies had expressed doubts about any apparent benefit for chloroquine use against Covid-19, the latest research sparked further concerns because it claimed the drug was more likely to lead to higher mortality.
"Our conclusion is that this treatment does not reduce the risk of dying from COVID among hospital patients and that clearly has significant importance for the way patients are treated, not only in the United Kingdom, but all around the world", said Martin Landray, an Oxford professor of medicine and epidemiology who co-leads the study.
Questions were immediately raised about the findings, with one researcher - Professor Peter Horby who is leading the University of Oxford's large-scale 10,000-patient RECOVERY trial of coronavirus drugs - told the BBC that his team hadn't seen that safety signal in the prospective trial.
Two large COVID-19 studies of a drug touted by President Donald Trump that warned of the risk of unsafe side effects and death have now been retracted after the credibility of the database used came under question. Their data was compared with 3,132 patients who were given standard hospital care.
The researchers also found that the length of hospital stay was 33 per cent longer in the HCQ group and 38 per cent longer in the "hydroxychloroquine + azithromycin" group than in the no-HCQ group.
Mentioning the limitations of the research, they said the median age in their study was about the same age as that in other studies of hospitalised patients - 70 years - but since the patients were older, the findings might not apply to younger people with COVID-19.
The World Health Organization immediately suspended the hydroxycholoroquine arm of its global Solidarity trial pending a safety review.
In some patients with severe COVID-19, the study said a large amount of cytokines are released in the body all at once, causing the immune system to damage the function of organs such as the lungs - a process known as a "cytokine storm".
"This is not a treatment for COVID-19".
Indian pharmaceutical companies, especially Ipca Laboratories and Zydus Cadila Ltd, are two of the world's largest manufacturers of hydroxychloroquine, and the hype surrounding the repurposed anti-malaria drug had led the two companies to scale up production to allow for sufficient inventories for domestic market and exports.
The decision to resume came as The Lancet issued a correction after more than 100 scientists and medical professionals raised questions about integrity of data analysed in the study.
On June 4, the results of first randomised clinical trial on study of HCQ as a prophylaxis showed no significant benefit in preventing COVID19 in high risk individuals.
The study prompted a media storm, particularly after President Donald Trump revealed at a press conference he was taking the drug prophylactically to ward off the coronavirus.
Coronavirus treatment trials that include hydroxychloroquine will continue following a massive research controversy, the World Health Organization announced.
On Friday, results from a fourth randomised controlled trial - carefully designed human experiments considered the most robust form of clinical investigation - showed it had no impact against the virus.
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The first major study of hydroxychloroquine as a treatment for COVID-19 found it did not protect against the infection. They also suggested taking the drug with the mineral zinc will help improve the immune system.