UPDATE 1-FDA approves Flexion's knee pain drug, shares surge

(Adds CEO and analysts' comments, shares)

Oct 6 (Reuters) - Flexion Therapeutics Inc said on Friday the U.S. Food and Drug Administration approved its injectable drug, Zilretta, to treat moderate-to-severe osteoarthritis-related knee pain, sending its shares soaring 18 percent.

The approval comes at a time when U.S. federal authorities are implementing a slew of measures to cut down the supply of opioid painkillers amid their continuous abuse, with President Donald Trump in August declaring the opioid epidemic a national emergency.

The drug would be priced at about $500 for a single injection, Flexion's CEO Mike Clayman told Reuters, adding that it would be launched in the coming month.

Zilretta, a modified formulation of a commonly used corticosteroid, could bag potential peak sales of more than $750 million according to Northland Capital Markets analyst Carl Byrnes.

"Zilretta ... has the potential to be a gamechanger in osteoarthritis knee pain treatment," Wells Fargo analyst David Maris said in a client note ahead of the regulator's decision.

Osteoarthritis knee pain is a degenerative joint disease that affected more than 14 million Americans in 2015.

(Reporting by Divya Grover and Tamara Mathias in Bengaluru; Editing by Martina D'Couto)