Washington: The United States has delivered two million doses of the antimalarial medicine hydroxychloroquine (HCQ) to Brazil to fight COVID-19, the White House said on Sunday, though the drug has not been proven effective against the coronavirus.

"HCQ will be used as a prophylactic to help defend Brazil's nurses, doctors, and healthcare professionals against the virus. It will also be used as a therapeutic to treat Brazilians who become infected," a statement said.

It said the US would soon also send 1,000 ventilators to Brazil, the epicentre of South America's outbreak with nearly 5,00,000 confirmed cases.

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"We are also announcing a joint United States-Brazilian research effort that will include randomized controlled clinical trials," it added.

President Donald Trump is an outspoken fan of HCQ, which has been used to treat malaria for decades as well as the autoimmune disorders lupus and rheumatoid arthritis.

He has previously said he is taking it himself in the hope of avoiding infection with the virus.

There is currently no evidence from a randomised controlled trial (RCT) considered the gold standard of clinical investigation for HCQ's use either to treat or prevent COVID-19.

There are also fears that it may in fact worsen coronavirus patient's outcomes.

A paper published in The Lancet last week concluded that treating people who have COVID-19 with hydroxychloroquine and a related compound chloroquine did not help them and might have increased the risk of abnormal heart rhythms and death.

The study was not an RCT, and more than 100 clinicians and scientists have since questioned the authenticity of a hospital database it relied on to reach its conclusions.

HCQ has been granted an emergency use authorisation for COVID-19 in the US for patients under close heart monitoring.

The Food and Drug Administration has asked doctors not to prescribe it widely or outside of several clinical trials that are underway.

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Like Trump, Brazilian President Jair Bolsonaro is an advocate of HCQ and has sacked two health ministers who clashed with him over his desire to expand its use.

Despite losing nearly 30,000 people to the virus, Bolsonaro has railed against the "tyranny" of lockdowns and called for the country's soccer season to resume.

The US has lost more than 1,06,000 people to the virus, by far the country with the highest number of deaths.

The World Health Organisation said last week it was temporarily halting testing of the HCQ for COVID-19 over growing safety concerns, including those raised in The Lancet paper.