(Adds details, CEO comment; updates shares)
By Natalie Grover
Dec 22 (Reuters) - The U.S. Food and Drug Administration approved BioCryst Pharmaceuticals Inc's single-dose flu drug, in what the company says is the agency's first ever approval for an intravenous drug to fight influenza.
The drug is intended for adults with acute uncomplicated influenza who are unable to swallow pills such as Gilead Sciences Inc's Tamiflu or inhale GlaxoSmithKline Plc's Relenza because of upper respiratory problems.
"An (intravenous) drug would ensure that an appropriate dose is administered, which is a concern for oral and inhaled drugs in severely ill patients," Needham & Co analyst Serge Belanger said.
BioCryst's peramivir injection, to be sold as Rapivab, is the first antiviral influenza treatment approved by the FDA in fifteen years, the company said on Monday.
Rapivab inhibits the enzyme neuraminidase, which is critical to the spread of influenza.
The drug has limited commercial potential, but stockpiling orders are likely to drive sales, analysts said.
Roth Capital Partner analyst Ed Arce estimated a $120 million stockpiling order from the U.S. Department of Health and Human Services (HHS) in the first quarter of 2015.
BioCryst Chief Executive Jon Stonehouse said he expected the drug to be available in time for this year's flu season.
A single 600 mg dose of Rapivab via intravenous infusion for 15-30 minutes is recommended for adults who have shown flu symptoms for no more than two days, the company said.
Rapivab was developed under a $234.8 million contract from Biomedical Advanced Research and Development Authority of the HHS. It was granted an "emergency use authorization" during the October 2009 swine flu pandemic.
The drug was launched in Japan in January 2010 by Shionogi & Co Ltd under the name Rapiacta. Later that year, it received approval in South Korea to treat influenza, and for use against swine and bird flu.
BioCryst is also developing a broad-spectrum anti-viral, BCX4430, with the National Institute of Allergy and Infectious Diseases for viruses that pose a threat to health and national security, including Ebola.
BioCryst shares were slightly down at $11.09 in afternoon trading on the Nasdaq, after rising as much as 3 percent earlier.
(Additional reporting by Samantha Kareen Nair; Editing by Joyjeet Das and Kirti Pandey)