An antiviral drug called remdesivir is being considered a potential treatment for the novel coronavirus after it produced promising results in two hospitalized patients.

“It basically stops the production of the virus,” Dr. Gregory Poland, an infectious diseases expert and director of the Mayo Clinic’s Vaccine Research Group in Rochester, Minnesota, told NBC News.

It was used to treat the first known case of COVID-19 in the U.S. after the unidentified 35-year old man failed to improve after seven days. The doctors wrote in the New England Journal of Medicine that they treated him “with intravenous remdesivir” on the evening of day seven and that by day eight, his symptoms began to go away.

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It is unclear how much, if at all, the drug affected the recovery process.

A second patient treated at the Providence Regional Medical Center in Everett, Washington credits the drug with his recovery.

Gilead, the biotech company that developed the drug, said in a statement that “remdesivir is an investigational antiviral with limited data at this time. It is not approved anywhere globally and has not been demonstrated to be safe or effective for any use.”

The company is currently supporting five clinical trials around the world to study remdesivir as a potential COVID-19 treatment. The two aforementioned patients received the drug through compassionate use programs.

Gilead said Sunday it was temporarily putting emergency access to remdesivir on hold due to a spike in compassionate-use requests.

First results of the clinical trials are expected in late April.