The US Food and Drug Administration (FDA) on Friday cautioned against the use of malaria drugs, hydroxychloroquine and chloroquine, in COVID-19 patients outside of hospitals and clinical trials, citing risks of serious heart rhythm problems.
The agency's announcement comes a day after the European Union's drug regulator warned of the drugs' side effects and urged medical professionals to closely monitor patients on the medicines.
The FDA said it was aware of increased use of these medicines through outpatient prescriptions and the drugs could cause abnormal heart rhythms and dangerously rapid heart rate.
Decades-old hydroxychloroquine has been touted by US President Donald Trump as a "game changer" in the fight against the novel coronavirus and anecdotal reports that it may provide some benefit have spurred sales of the drug.
However, the drug provided no benefit and potentially higher risk of death for patients at US veterans hospitals, according to an analysis that was submitted for expert review earlier this week.
The FDA has allowed healthcare providers to use the drug for COVID-19 through its emergency use authorisation, but the drug is not approved to treat the disease.
The heart rhythm risks may increase when the medicines are combined with other drugs, such as antibiotic azithromycin, as well as in patients with existing heart and kidney disease, the agency said on Friday.