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 Flexion recently announced the FDA approval of Zilretta for OA knee pain. Zilretta’s US sales will accelerate when the product’s label includes repeat administration – Pharmavitae Analytics predicts that Flexion’s ongoing Phase III safety trial will clear the way for repeat intra-articular administration in 2019. Flexion will search externally to replenish and grow its clinical pipeline – Buoyed by confidence in Zilretta’s future revenue, and with one investigational drug in preclinical development for OA and no clinical-stage candidates, Flexion will aggressively seek in-licensing opportunities.



Analyst comment

Pharmavitae Analytics forecasts that Zilretta (triamcinolone acetonide extended-release injectable suspension), the only US Food and Drug Administration (FDA)-approved, extended-release, intra-articular treatment for osteoarthritis (OA) knee pain, will reach peak sales of $768m in the US (see Figure 1). Pharmavitae Analytics expects that Zilretta will experience strong market penetration among OA knee pain patients currently receiving intra-articular corticosteroid injection treatment. The drug will also experience high market uptake by patients with both OA knee pain and type 2 diabetes who cannot receive immediate-release corticosteroid treatment due to potential blood glucose disruption. Pharmavitae Analytics additionally anticipates that Zilretta’s revenue will receive a boost when the product’s label is updated to include a repeat administration indication in Q2 2019.




On 6 October 2017, Flexion Therapeutics announced that the FDA had approved Zilretta as an intra-articular injection for OA knee pain (Flexion, 2017a). Zilretta, which is not currently intended for repeat administration (Flexion, 2017a), was approved based on pivotal Phase III data demonstrating that a single administration of the corticosteroid achieved significant pain relief compared with placebo at 12 weeks (Flexion, 2016; 2017a). The product’s label also includes results from a Phase II study in type 2 diabetes patients, which suggest that Zilretta avoids the significant rise in blood glucose observed with immediate-release corticosteroid treatment (Flexion, 2017a; 2017b). Flexion expects that Zilretta will be available in the US by the end of October 2017 (Flexion, 2017a).




Pharmavitae Analytics forecasts that Zilretta will reach peak sales of $768m in the US, with a label update to include repeat administration anticipated in Q2 2019. Flexion expects topline results from an ongoing open-label, Phase III trial evaluating the safety of repeat administration of Zilretta for OA knee pain in Q3 2018 (Flexion, 2017c; 2017d), and Pharmavitae Analytics anticipates that the placebo-like safety of Zilretta that was demonstrated in the pivotal Phase III study (Flexion, 2016) will translate into long-term safety, as evidenced in the Phase III repeat administration trial.

Lack of direct competition in the medium term – Zilretta will successfully compete for a share of the OA knee pain market, despite carrying a significantly higher price than the generic corticosteroid intra-articular injection competition, due to it being the only extended-release intra-articular injection approved by the FDA for OA knee pain in the US. Zilretta will also provide an attractive option for patients with both OA knee pain and type 2 diabetes, representing 20% of the OA knee pain population in the US (Flexion, 2017c), based on Phase II results suggesting that the drug avoids the blood glucose spike associated with immediate-release corticosteroid treatment in these patients (Flexion, 2017b).


Revenue growth – Pharmavitae Analytics forecasts that Zilretta’s label will be updated to include a repeat administration indication for OA knee pain in Q2 2019, based on topline safety data from the ongoing, open-label Phase III trial expected in Q3 2018 (Flexion, 2017c; 2017d), providing a boost in US sales.


fda figure1


Pipeline revamp

Flexion plans to build its pipeline on the foundation of Zilretta’s successful launch through external and internal investment, and remains focused on the localized treatment of musculoskeletal disease. The company’s chief executive officer, Michael Clayman, noted in an interview in February 2017 that Flexion has the commercial infrastructure to independently market Zilretta in the US (Scrip, 2017), and it is now on the verge of hiring a team of over 100 sales representatives for Zilretta’s launch. The company plans to fill its empty clinical pipeline through in-licensing and internal R&D, and maintain a streamlined portfolio of injectable drugs for localized pain (Flexion, 2017c).


Flexion (2016) Flexion Therapeutics Reports Primary Endpoint Met in Pivotal Phase 3 Trial of Zilretta™ in Knee Osteoarthritis. Available from: [Accessed 9 October 2017].

Flexion (2017a) Flexion Therapeutics Announces FDA Approval of Zilretta™ (triamcinolone acetonide extended-release injectable suspension) for Osteoarthritis (OA) Knee Pain. Available from: [Accessed 9 October 2017].

Flexion (2017b) Flexion Therapeutics to Present Data on Zilretta™ (FX006) at the American Diabetes Association's 77th Scientific Sessions: Full findings from Phase 2 study in patients with knee osteoarthritis and Type 2 diabetes show Zilretta avoids the significant rise in blood glucose seen with an immediate-release corticosteroid. Available from: [Accessed 9 October 2017].

Flexion (2017c) Zilretta FDA Approval Call. Available from: [Accessed 9 October 2017].

Flexion (2017d) Flexion Therapeutics Initiates Clinical Trial to Evaluate the Safety of Repeat Administration of Zilretta™ (FX006) in Patients with Osteoarthritis of the Knee. Available from:[Accessed 9 October 2017].

Scrip (2017) Flexion CEO Makes The Case For Zilretta. Available from: [Accessed 9 October 2017].

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