Shares of the company at last check were down 1.3% to $75.44.
Gilead Sciences said the placebo-controlled trial will enroll about 60 healthy subjects, aged 18-45, in the United States to form the basis for the further study, particularly in patients whose disease has not progressed to require hospitalization."
"Based on current scientific understanding, the upper respiratory tract is the most prevalent site of SARSCoV-2 infection early in disease," Merdad Parsey, Gilead Sciences' chief medical officer, said in a statement.
"Delivering remdesivir directly to the primary site of infection with a nebulized, inhaled solution may enable more targeted and accessible administration in non-hospitalized patients and potentially lower systemic exposure to the drug."
Remdesivir is a broad-spectrum antiviral medication that has proven effective at helping patients with severe symptoms of Covid-19 recover.
The company first said last month that it would be starting trials of an inhaled version of remdesivir after receiving the go-ahead from the Food and Drug Administration.
While Gilead has received FDA emergency use authorization for an intravenous form of remdesivir, it has not yet been formally approved as a coronavirus treatment.
Parsey said that "additional clinical trials evaluating remdesivir in combination with anti-inflammatory medicines, in vulnerable patient populations and in outpatient settings, are ongoing or planned to initiate in the near future."
Gilead Sciences said recently that it will price remdesivir at $2,340 for a five-day treatment, well below what it says would be market prices for the drug.