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Chloroquine and hydroxychloroquine have received intense attention because of positive results from small studies and an endorsement from President Donald Trump, who said, “I feel good about it.” The drugs decrease acidity in endosomes, compartments that cells use to ingest outside material and that some viruses co-opt during infection. But SARS-CoV- 2's main entryway is different: It uses its so-called spike protein to attach to a receptor on the surface of human cells. Studies in cell culture have suggested chloroquine can cripple the virus, but the doses needed are usually high and could cause severe toxicity. “Researchers have tried this drug on virus after virus, and it never works out in humans,” says Susanne Herold, an expert on pulmonary infections at the University of Giessen.
Results from COVID-19 patients are murky. Chinese researchers who treated more than 100 patients touted chloroquine's benefits in a letter in BioScience, but they did not publish data. And WHO says “no data has been shared” from more than 20 other COVID-19 studies in China using chloroquine or hydroxychloroquine. French microbiologist Didier Raoult and colleagues published a study of hydroxychloroquine in 20 COVID-19 patients that concluded the drug had reduced viral load in nasal swabs. (It seemed to work even better with the antibiotic azithromycin.) But the trial, reported in the International Journal of Antimicrobial Agents, was not randomized, and it didn't report clinical outcomes such as deaths.
Hydroxychloroquine might actually do more harm than good. It has many side effects and can, in rare cases, harm the heart—and people with heart conditions are at higher risk of severe COVID-19, says David Smith, an infectious disease physician at the University of California, San Diego. “This is a warning signal, but we still need to do the trial,” he says. There have also been reports of chloroquine poisoning in people who self-medicated.
