Flexion Therapeutics (NSDQ:FLXN) said today that it submitted a new drug application to the FDA for its extended-release steroid injection Zilretta. The Burlington, Mass.-based company won Fast Track status from the watchdog for its osteoarthritis injection last year.

The new drug application is based on data from a pivotal phase III clinical trial evaluating Zilretta in patients with moderate to severe osteoarthritis knee pain. The randomized, double-blind study enrolled 484 patients at 37 centers to compare the injection to a placebo and a commonly injected intra-articular corticosteroid. In both comparisons, patients who were treated with Zilretta had a statistically significant reduction in average daily pain after 12 weeks. No drug-related serious adverse events were reported.

Flexion touts Zilretta as the 1st intra-articular, extended-release therapy for patients with knee osteoarthritis pain. The injection uses microsophere technology to combine a commonly administered, short-acting corticosteroid with a polylactic-co-glycolic acid matrix.

“The submission of our 1st NDA is a major milestone for Flexion Therapeutics. Based on our pivotal data, we believe that Zilretta has the potential to be the 1st intra-articular, extended-release treatment for the many millions of patients who suffer with knee OA,” president & CEO Dr. Michael Clayman said in prepared remarks. “I am grateful to our dedicated employees, clinical collaborators and board of directors for their commitment to advancing novel therapeutics that address unmet medical needs for patients with musculoskeletal conditions.”