NEW YORK (TheStreet) -- Shares of Flexion Therapeutics  (FLXN) - Get Report plummeted 22.6% to $15 in after-hours trading Wednesday after the company announced the FDA had placed a clinical hold on patient enrollment and dosing in a Phase 2b trial of the company's osteoarthritis treatment.

Flexion had not received written notice of the hold as of the time it issued the press release, but the company said the FDA indicated through verbal conversation Tuesday that the hold stems from a single occurrence of an infection in the injected knee joint of a patient in the trial.

The trial is evaluating FX006 in patients with osteoarthritis of the knee. The treatment is a non-opioid, sustained-release, intra-articular formulation of triamcinolone acetonide that targets moderate to severe osteoarthritis pain.

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"We will work closely with FDA to provide the agency with all appropriate information and data required to expedite their review and evaluation of this event," said Michael Clayman, M.D., Flexion's President and CEO. "Once the FDA has completed its review, we can better assess the impact this clinical hold will have on our development program timeline for FX006."

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