The U.S. Food and Drug Administration (FDA) on Thursday approved Gilead's antiviral drug remdesivir as a treatment for COVID-19, although a large trial by the World Health Organization (WHO) showed it did not help hospitalized patients. 

Remdesivir is the first and only approved COVID-19 treatment in the U.S., Gilead said in a statement. 

Given intravenously, it was one of the drugs used for treating U.S. President Donald Trump after he was diagnosed of COVID-19. 

The FDA's formal approval comes just hours before the president's final debate with Democratic rival Joe Biden ahead of the November 3 presidential election. 

Remdesivir has been available under an FDA emergency use authorization (EUA) since May, after a study led by the National Institutes of Health showed it reduced hospital stays by five days. 

However, the WHO said its global trial of COVID-19 therapies found that remdesivir did not have a substantial effect on patients' length of hospital stay or chances of survival. 

Remdesivir has become the standard of care for patients hospitalized with severe COVID-19 even though it has not been shown to improve survival. The drug also has not been proven to significantly help moderately ill patients and many doctors remain wary of using it in patients with less severe illness. 

Gilead has questioned the potential for bias in the WHO study, which was not "blinded," meaning that both the patients and their doctors were aware of which treatments were being used. 

Remdesivir, which will be sold under the brand name Veklury, costs 3,120 U.S. dollars for a five-day treatment course, or 2,340 dollars for government purchasers such as the Department of Veterans Affairs. Shares of Gilead rose 4.3 percent in after-hours trading to 63.30 dollars. 

"The formal FDA approval doesn't change our (sales) estimates or outlook for remdesivir given it has already been branded standard-of-care prior to formal approval," Raymond James analyst Steven Seedhouse said in a research note, calling the prescribing guidelines and approval "pretty much a best case for Gilead" given the WHO results questioning remdesivir's benefits.

Gilead said it is currently meeting demand for the drug in the U.S. and anticipates meeting global demand by the end of October. 

The company said Veklury has regulatory approvals or temporary authorizations in about 50 additional countries. 

Also on Thursday, the FDA issued a new emergency use authorization for remdesivir to treat hospitalized pediatric patients under age 12 who weigh enough to receive an intravenous drug. 

Gilead said it is still working to understand the full potential of remdesivir in different settings and as part of combination therapy approaches. The company is also developing an inhaled version of the drug that might be used outside a hospital setting, if approved.

(With input from Reuters.)

(Cover: Gilead company is seen from afar in Oceanside, California, U.S. April 29, 2020. /Reuters)