Older malaria drugs are being studied, and in some cases used, to treat or try to prevent infection with the new coronavirus, even though there is no firm evidence to show they are effective.

Studies are underway in a number of countries, including China, France and the United States, to see whether the pills - chloroquine and hydroxychloroquine - may have a role to play in the rapidly spreading pandemic.

US President Donald Trump has touted the malaria drugs as "a game changer." But the Food and Drug Administration and other health experts said trials must first ensure the medicines are effective and safe for use in this patient population.

WHY ARE MALARIA DRUGS UNDER CONSIDERATION?

There are currently no vaccines or US-approved treatments for the highly contagious COVID-19 respiratory illness that has killed more than 18,000 worldwide, so even the most severely ill patients largely receive only supportive care such as breathing assistance.

On its website, the Centers for Disease Control and Prevention says some US clinicians have reported anecdotal use of hydroxychloroquine at different doses.

Chloroquine is a synthetic form of quinine, which is found on the bark of the cinchona plant. It has been used for hundreds of years in South America to treat fever.

Chloroquine was first synthesized in the 1930s. A version called hydroxychloroquine, in use since the 1950s, is considered to be less toxic, according to studies. Both drugs can cause serious side effects, including vision loss, heart problems or even death, if used incorrectly.

The drugs are used to combat malaria, which is caused by a parasite spread through mosquito bites, because they interrupt its ability to digest a host's blood cells.

Scientists have detailed biochemical proprieties of chloroquine that indicate it could be used against some viral infections. These include direct antiviral effects, such as blocking steps needed by certain viruses to replicate, and its ability to suppress production and release of proteins involved in inflammatory complications of several viral diseases.

In addition to malaria, hydroxychloroquine is also used to treat lupus and rheumatoid arthritis.

WHAT DOES THE DATA SAY?

Data has begun to emerge from some coronavirus trials, but most information so far is preliminary.

A French team last week said initial results from a 24-patient trial of hydroxychloroquine showed that 25 percent of patients given the drug still carried the coronavirus after 6 days, compared with 90 percent of patients given a placebo. But the trial is small and results on patient outcomes are still awaited.

Chinese researchers last month reported trial results showing that chloroquine treatment of COVID-19 patients had clinical and virologic benefit versus a comparison group. It has been added as a recommended treatment for the illness in China, where the virus first emerged in December.

This week, the Journal of Zhejiang University reported disappointing results from a 30-patient Shanghai study of hydroxychloroquine. It showed the drug worked no better than standard care for patients with COVID-19.

The University of Minnesota has launched a 1,500-person trial to see whether hydroxychloroquine can prevent or reduce the severity of COVID-19 in people exposed to the virus - including health-care workers and family members of infected people.

Other trials of the malaria drugs are ongoing or set to start in the United Kingdom, Norway and Thailand.

New York Governor Andrew Cuomo, whose state is the epicenter of the US outbreak with more than 25,000 cases, on Sunday said it had acquired hundreds of thousands of doses of the malaria drugs to use in a clinical trial.

IS THERE ENOUGH TO GO AROUND?

In the United States, prescriptions for chloroquine and hydroxychloroquine have already spiked and are in short supply, according to pharmacists.

Several makers of the generic medicines said they are increasing production of chloroquine pills. Teva Pharmaceuticals Industries Ltd, Mylan NV and Bayer AG have donated large quantities of the drugs to health authorities.

PRESCRIPTION ONLY!

Health officials caution that no one should be taking these drugs to treat or prevent coronavirus infection without medical supervision and a prescription.

In Arizona, a man died and his wife was hospitalized after taking a non-medical form of chloroquine used to fight parasites in aquariums.

"Given the uncertainty around COVID-19, we understand that people are trying to find new ways to prevent or treat this virus, but self-medicating is not the way to do so,” said Dr. Daniel Brooks, medical director of the poison and drug information center at Arizona-based Banner Health.