The first reported use of an experimental Gilead Sciences Inc. drug to fight the novel coronavirus has encouraged doctors to support further testing of the medication.

Gilead’s remdesivir was given to the first U.S. case, a 35-year-old man who developed pneumonia after he tested positive for the 2019-nCoV virus and was hospitalized in an airborne-isolation unit at Providence Regional Medical Center Everett in Washington state for observation.

“To my knowledge, this is the first reported case in the world where this drug has been used in a human application against this virus,” Jay Cook, chief medical officer at the center, told reporters on a conference call Friday. “At the time, we felt the benefits of using this drug outweighed whatever potential risk there might be and we obtained his informed consent.”

The patient’s pneumonia appeared to improve within a day, with no obvious side effects, after the intravenous drug was administered, his doctors reported in the New England Journal of Medicine on Friday. The finding should encourage randomized, controlled clinical trials to determine its safety and efficacy for treating 2019-nCoV infections, they said.

The drug was approved for use on compassionate grounds. It is not licensed or approved anywhere in the world, and hasn’t been demonstrated to be safe or effective for any use, Foster City, California-based Gilead said in a statement.

The drugmaker, known for its antivirals to fight hepatitis C and HIV, is working with global health authorities to respond to the coronavirus outbreak through the “appropriate experimental use” of remdesivir, Gilead said. It is also cooperating with individual researchers and clinicians to lend its knowledge and antiviral expertise to help patients fight 2019-nCoV.

Remdesivir, a novel, so-called nucleotide analogue prodrug, was developed with the Ebola crisis in mind, said Scott Lindquist, the state epidemiologist for infectious disease at Washington’s Department of Health.

“There’s been very limited use around the country,” he told reporters on a conference call. “We do know that the manufacturer of this product is trying to work with China to do studies and provide this overseas, along with other antivirals that are under investigation.”

Preclinical studies of remdesivir and an older compound known as NHC indicate both are broadly capable of countering “every bat and human and animal coronavirus we’ve tested,” said Mark Denison, director of infectious diseases and a pediatrics professor at the Vanderbilt University School of Medicine.

Denison and colleagues used a National Institutes of Health grant to screen compounds that are capable of thwarting a broad range of coronaviruses. Their five-year study found two — remdesivir and NHC — seem to block virus replication by interfering with their ability to correctly copy their genetic material.

Their studies found both are promising therapies for infections caused by SARS, mouse hepatitis virus, and bat coronaviruses, Denison said in a phone interview. He said he predicts they will also be effective against 2019-nCoV, possibly as a dual therapy to both prevent and treat disease.

Combinations of antiviral treatments have shown to be effective at suppressing HIV while avoiding the emergence of drug-resistant strains.

“Combination therapy for emerging viruses is the way to go,” Denison said. “These are both exciting drugs that work well independently. It would, of course, make sense to consider multiple combinations of drugs that work independently.”

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