The US drugs regulator has controversially approved the anti-malarial drugs hydroxychloroquine and chloroquine to treat seriously ill patients with COVID-19.

The emergency approval for use of the older-generation drugs in hospitals was granted by the FDA over the weekend, despite concern over a lack of safety or efficacy data for this indication.

In a letter granting approval for healthcare workers to administer oral formulations of the drugs for the treatment of COVID-19 in adolescents and adults, the FDA chief scientist, Rear Admiral Denise Hinton, said the decision was based on a risk–benefit assessment.

“Based on the totality of scientific evidence available to the FDA, it is reasonable to believe that chloroquine phosphate and hydroxychloroquine sulfate may be effective in treating COVID-19,” she wrote to the US Department of Health and Human Services.