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. [www.scientificamerican.com]

Chloroquine and hydroxychloroquine have been hypothesized to work against COVID-19 by changing the pH required for SARS-CoV-2 to replicate. Given their use in autoimmune disorders, these medications could also play a role in dampening the immune response to the virus—which can be deadly in some patients.

But these drugs’ cardiac toxicity is a concern, Keshtkar-Jahromi says. There have been some reports of myocarditis, or inflamed heart tissue, in people with COVID-19 who have not taken chloroquine or hydroxychloroquine. If patients receiving one of these medications die of heart complications—and are not in a clinical trial—doctors cannot know if the drug contributed to higher chance of death.*

A drug that modulates the immune response could also make someone more vulnerable to other viral or bacterial infections. “It’s a double-edged sword,” says Sina Bavari, chief science officer and founder of Edge BioInnovation Consulting in Frederick, Md., who co-authored Keshtkar-Jahromi’s article in the American Journal of Tropical Medicine. Giving a drug to suppress the immune system has to be done with extreme care.

“We are not saying, ‘Don’t [prescribe chloroquine],’” Bavari says. “We are saying, ‘More data is needed to better understand how the drug works—if it works.’”