New York: A team of US doctors has claimed that hydroxychloroquine, an anti-malarial drug termed potential "game-changer" for COVID-19 by President Donald Trump, has improved the survival and recovery odds for about 90 per cent of patients infected with the virus.

In a letter to Arizona Governor Doug Ducey, the Association of American Physicians and Surgeons (AAPS) presented a frequently updated table of studies that report results of treating COVID-19 with the chloroquine and hydroxychloroquine drugs.

They presented data on 2,333 patients treated with hydroxychloroquine in China, France, South Korea, Algeria, and the US.

It shows 91.6 per cent of those who got the drug fared better after treatment.

The antiviral properties of these drugs have been studied since 2003. Particularly when combined with zinc, they hinder viral entry into cells and inhibit replication. They may also prevent overreaction by the immune system, which causes the cytokine storm responsible for much of the damage in severe cases, the AAPS explained.

In a letter, the AAPS team urged that doctors should not wait for results of gold standard tests of the drug to start using it for coronavirus patients and should instead base their use of it on reasonable interpretations of limited available data.

Peer-reviewed studies published from January through April 20, this year, provide clear and convincing evidence that hydroxychloroquine may be beneficial in COVID-19, especially when used early, they stated.

AAPS's endorsement of the drug comes after the study from Veterans Health Administration medical centers showed that hydroxychloroquine has no benefit in treating patients with the disease.

Meanwhile, on April 24, the US Food and Drug Administration (FDA) issued fresh guidelines, cautioning people against over-the-counter use of hydroxychloroquine or chloroquine for Covid-19 outside of the hospital setting or a clinical trial due to the risk of heart rhythm problems.

The FDA said it is aware of reports of serious heart rhythm problems in patients with Covid-19 treated with hydroxychloroquine or chloroquine, often in combination with azithromycin and other QT-prolonging medicines.

"We are also aware of the increased use of these medicines through outpatient prescriptions. Therefore, we would like to remind healthcare professionals and patients of the known risks associated with both hydroxychloroquine and chloroquine," the agency said in a statement.