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Chloroquine, a drug that has been used to prevent and treat malaria, has shown promise in being a potential treatment for the novel cornavirus sweeping the globe, President Trump said Thursday.

On Wednesday, the World Health Organization (WHO) announced a multicountry clinical trial of four drugs as possible COVID-19 treatments -- one of those drugs is chloroquine.

Chloroquine is widely available now and could be used off-label, but FDA commissioner Stephen Hahn explained that officials want a formal study to get good information on its safety and effectiveness. The drug was first used to treat malaria in 1944.

"We're looking at drugs that are already approved for other indications" as a potential bridge or stopgap until studies are completed on other drugs under investigation, Hahn said.

When people become infected with COVID-19, the virus' protein spikes bind to receptors on the outside of human cells. Chloroquine has worked by interrupting that process with SARS. It could potentially interfere with COVID-19's ability to bind to cells.

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"The way that it worked against SARS was by preventing of the attachment of the virus to the cells. Chloroquine interfered with the attachment to that receptor on the cell membrane surface," Dr. Len Horovitz, a pulmonologist and internist at Lenox Hill Hospital in New York City, told ABC News. "So it’s disrupting a lock and key kind of mechanism of attachment."

Chloroquine is also sometimes used as a treatment for rheumatoid arthritis and amebiasi, according to MedlinePlus. Side effects from the drug include muscle problems, loss of appetite, diarrhea, and skin rash, while more serious ones include problems with vision and muscle damage, according to the American Society of Pharmacists.

However, there remains no proven treatment for the novel coronavirus, from which most people recover. The virus has infected over 230,000 worldwide and killed more than 9,300.

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