Shares of Flexion Therapeutics (FLXN) soared 28% in after-hours trade on Tuesday after it had announced that its phase 3 trial hit the primary endpoint of the study. The phase 3 trial recruited 486 patients and split them up into three different dose groups. One group of patients took a single IA injection of 40 mg of Zilretta, one group of patients took saline -- a placebo-- and the last set of patients took 40 mg of an active drug known as immediate-release TCA. 

The primary endpoint was looking for the amount of pain relief the company's drug Zilretta could achieve compared to the placebo. The primary endpoint of the study was met with Zilretta achieving statistically significant pain relief compared to the placebo from week 1 through week 16-- p <0.0001. In addition, Zilretta obtained statistical significance in a couple of scores on a Knee Injury and Osteoarthritis Outcome Score -- KOOS -- quality of life subscale. The drug performed better against placebo and active in WOMAC-A -- pain --, WOMAC-B -- stiffness, WOMAC-C -- function. 

Zilretta has already received FDA Fast Track Designation, which gives it a faster track for approval. If all goes well with filings and communications between the FDA, Flexion expects to file a New Drug Application -- NDA -- by the second half of 2016.