Remdesivir is an antiviral medication that targets a range of viruses. It was originally developed over a decade ago to treat hepatitis C and a cold-like virus called respiratory syncytial virus (RSV). Remdesivir wasn’t an effective treatment for either disease. But it showed promise against other viruses.

Researchers tested remdesivir in clinical trials during the Ebola outbreak. Other investigational medications worked better, but it was shown to be safe for patients. Studies in cells and animals suggested that remdesivir was effective against viruses in the coronavirus family, such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).

Remdesivir works by interrupting production of the virus. Coronaviruses have genomes made up ribonucleic acid (RNA). Remdesivir interferes with one of the key enzymes the virus needs to replicate RNA. This prevents the virus from multiplying.

Researchers began a randomized, controlled trial of the antiviral in February 2020 to test whether remdesivir could be used to treat SARS-CoV-2, the coronavirus that causes COVID-19. By April, early results indicated that remdesivir accelerated recovery for hospitalized patients with severe COVID-19. It became the first drug to receive emergency use authorization from the U.S. Food and Drug Administration (FDA) to treat people hospitalized with COVID-19.

Researchers have now completed the trial, known as the Adaptive COVID-19 Treatment Trial (ACTT-1). The study was funded by the National Institute of Allergy and Infectious Diseases (NIAID). The final report appeared in the New England Journal of Medicine on October 8, 2020.

Scientists randomly assigned 1,062 hospitalized COVID-19 patients to receive remdesivir or a placebo plus standard treatment. The patients received an intravenous infusion of remdesivir or placebo for up to 10 days.

The final results showed that the antiviral treatment was beneficial, consistent with the preliminary findings. Patients who received remdesivir were quicker to recover, which was defined as being medically stable enough to be discharged from the hospital. The median recovery time was 10 days with remdesivir compared to 15 days for the placebo group. Patients given remdesivir were more likely to have improved by day 15.

Remdesivir also improved mortality rates for those receiving supplemental oxygen (4% with remdesivir versus 13% with placebo at day 29 of treatment). All-cause mortality among all patients was 11% with remdesivir and 15% with placebo at day 29, but this difference between the treatment groups was not large enough to rule out chance. The preliminary findings hadn’t shown an effect on mortality.

The study also suggested that remdesivir treatment may prevent patients from progressing to more severe respiratory disease. Those treated with remdesivir were less likely to need high levels of respiratory support. Remdesivir appeared to most benefit patients who were receiving supplemental oxygen.

“Our findings show that remdesivir is a beneficial treatment for patients with COVID-19,” says study author Dr. John Beigel of NIAID. “It may also help to conserve scarce health care resources, such as ventilators, during this pandemic.”

The findings show that remdesivir alone isn’t a sufficient treatment for all patients but does provide some benefit. Studies are underway to evaluate remdesivir in combination with other therapies.