FDA approves Flexion Therapeutics' pain treatment By: MarketMinute.com Stock News October 06, 2017 at 17:18 PM EDT The Food and Drug Administration approved Flexion Therapeutics Inc.'s (Nasdaq: FLXN) non-opioid steroid injection to treat knee pain. Shares of the pharmaceutical soared $2.81 to close at $29.93. Related Stocks: Flexion Therapeutics