A study published on Thursday on the use of hydroxychloroquine in Brazil to treat Covid-19 found the drug ineffective, the latest blow to President Jair Bolsonaro's push for its widespread use.
The clinical trial, conducted at 55 hospitals across Brazil and published in the New England Journal of Medicine, tested whether hydroxychloroquine improved the condition of patients with mild to moderate cases of Covid-19, alone or in combination with the antibiotic azithromycin.
Bolsonaro's government has recommended since May that doctors in Brazil's public health system prescribe hydroxychloroquine or the related anti-malaria drug chloroquine, plus azithromycin, from the onset of symptoms of the new coronavirus.
Like US President Donald Trump, whom he admires, Mr Bolsonaro has touted the drug as a treatment for Covid-19. The far-right leader is even taking the drug himself, after coming down with the virus earlier this month.
However, a slate of randomized controlled trials (RCTs), considered the gold standard for clinical investigation, have found the drug is ineffective against coronavirus and has potentially damaging side effects.
The Brazilian RCT reached the same conclusion.
Brazil has essentially become the world's biggest testing ground for the drugs because of the Bolsonaro government's policy.
Among patients hospitalized with mild-to-moderate Covid-19, the use of hydroxychloroquine, alone or with azithromycin, did not improve clinical status at 15 days as compared with standard care, said the study, by doctors and researchers from a group called Coalition Covid-19 Brazil.
The group's members comprise two research institutes and six hospitals, including Albert Einstein Hospital in Sao Paulo, considered one of the best in Latin America.
The study, carried out on 667 patients, also found those on hydroxychloroquine developed clinical markers that increased their risk for heart and liver problems.
The authors acknowledged however that the study had several limitations, including that it was not blind - patients and their doctors knew whether they were in the control group or not.
The trial cannot definitively rule out either a substantial benefit of the trial drugs or a substantial harm, they said.
Brazil has the second-biggest number of infections and deaths in the pandemic, after the United States: 2.3 million and 84,000, respectively. Bolsonaro, who has downplayed the virus as a little flu, fiercely criticizes the economic impact of social distancing measures, arguing they are worse than the disease itself.