Shares of Flexion Therapeutics Inc. (FLXN - Get Report) soared 17.8% to $31.94 on Friday, Oct. 6, after the Burlington, Mass.-based firm received approval from the U.S. Food and Drug Administration for osteoarthritis knee pain treatment Zilretta.

"We believe that Zilretta has the potential to be a transformative medicine for the more than five million patients who receive an intra-articular injection for OA knee pain each year," said Flexion president and CEO Michael Clayman, M.D., in a statement.

Zilretta is a non-opioid medicine utilizing Flexion's microsphere technology.

Flexion said it expects the medicine to be available in the U.S. by the end of the month.

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