A drug that targets a weakness SARS-CoV-2, the virus that causes COVID-19, has has shown promise in an early study by the National Institutes of Health, the agency announced Thursday.

The experimental drug TEMPOL recently was tested in cell cultures by a research team from the NIH and other major U.S. institutions. They found that TEMPOL halts the activity of a viral enzyme called RNA replicase, limiting the severity of SARS-CoV-2 infection. Studies of the drug as a treatment for other diseases in animals also hint at the promise for use in COVID-19, they wrote in an article published Thursday in the journal Science

“Given TEMPOL’s safety profile and the dosage considered therapeutic in our study, we are hopeful,” said study lead Tracey A. Rouault, M.D. “However, clinical studies are needed to determine if the drug is effective in patients, particularly early in the disease course when the virus begins to replicate.”

More effective, accessible treatments for COVID-19 are “urgently” needed, said Diana W. Bianchi, M.D., director of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development. “An oral drug that prevents SARS-CoV-2 from replicating would be an important tool for reducing the severity of the disease.”

Currently, monoclonal antibody infusions are the most effective new treatments for high-risk patients with moderate COVID-19. Those drugs, a number of which have been given emergency authorization by the Food and Drug Administration, have been shown to significantly reduce progression to severe COVID-19, but their efficacy can be compromised by new virus gene variants.   

The next steps for TEMPOL include more animal studies. The researchers also plan to seek opportunities to evaluate the drug in a clinical study of COVID-19.