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Biologics Feature

Courtesy of Flexion Therapeutics, Inc., Wikimedia Commons and BruceBlaus

“Monumental” – FDA Approves Zilretta Extended Release Knee OA Drug

Walter Eisner • Tue, October 17th, 2017

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Fifty-two years after the FDA approved the first corticosteroid named Kenalog for use in humans, the agency has finally approved an extended-release version of the treatment.

Game Changer

On October 6, 2017, Flexion Therapeutics Inc. announced FDA approval of Zilretta, the "first and only extended-release, intra-articular injection for osteoarthritis knee pain." One Wall Street analyst called it a "monumental milestone" for the company. In a previous story in OTW we wrote that we believed FDA approval would be a game changer.

The product, according to the company, is a non-opioid medicine that uses the company's proprietary microsphere technology combining triamcinolone acetonide (TCA)—a commonly administered, short-acting corticosteroid—with a poly lactic-co-glycolic acid (PLGA) matrix to provide extended pain relief over 12 weeks.

And it was about time. For those 52 years TCA has been used as an anti-inflammatory treatment for ocular and skin problems.


Back in December 2016, Flexion submitted a new drug application (NDA) to the FDA for Zilretta and received Fast Track designation.

In announcing the submission, the company said the NDA was supported by previously reported results from a pivotal Phase 3 clinical trial.

“The randomized, double blind, placebo and active-comparator (immediate-release triamcinolone acetonide (TA)) controlled trial enrolled 484 patients at 37 centers worldwide. Data from the trial showed that Zilretta demonstrated a highly significant (p<0.0001) reduction in average daily pain versus placebo at week 12 (primary endpoint), with durable and clinically meaningful pain relief in patients with moderate to severe OA knee pain. In addition, compared to immediate-release TA, the most commonly injected intra-articular corticosteroid, Zilretta achieved statistical significance through 12 weeks on WOMAC A (pain), WOMAC B (stiffness) and WOMAC C (function)…”

The FDA-approved label also included positive results from a double-blind, randomized, parallel-group trial, which examined blood glucose concentrations in patients with type 2 diabetes.

Endpoints News reported that more than 4 million people suffering from osteoarthritis get these steroid shots, with 20% of those people having diabetes.

Indication and Important Safety Information

Indication: ZILRETTATM (triamcinolone acetonide extended-release injectable suspension) is indicated as an intra-articular injection for the management of osteoarthritis pain of the knee.

Limitations of Use: ZILRETTA is not intended for repeat administration.

Contraindication: ZILRETTA is contraindicated in patients who are hypersensitive to triamcinolone acetonide, corticosteroids or any components of the product.

The company offers a list of Warnings and Precautions, which can be found here.

Commenting on the approval, Andrew Spitzer, M.D., Co-Director, Joint Replacement Program, Cedars-Sinai Orthopaedic Center, said, "OA knee pain presents a host of challenges for patients and clinicians alike, and there has been very little innovation in this area in recent years. Zilretta is a groundbreaking new therapy, providing clinically meaningful pain relief with a safety profile that is similar to saline."

Flexion expects Zilretta will be available in the U.S. by the end of October.

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