Repeat administration of Zilretta (triamcinolone acetonide extended-release; Flexion Therapeutics) appears to be safe and well-tolerated in patients with osteoarthritis knee pain, according to results from a Phase 3b study.

In 2017, Zilretta was approved by the Food and Drug Administration for the management of pain associated with osteoarthritis (OA) of the knee, but was not intended for repeat administration. The product combines triamcinolone acetonide, a short-acting corticosteroid, with a poly lactic-co-glycolic acid matrix to provide pain relief over 12 weeks.

To evaluate the safety and tolerability of repeat administration, a Phase 3b single-arm, open-label trial was conducted in patients with symptomatic OA of the knee including those with advanced disease. Of a total of 208 patients who received a first injection of Zilretta, a second injection was administered to 179 patients (median time to second injection was 16.6 weeks). 

“Up to 52 weeks of radiographic data collected in this study revealed no adverse effects, including no evidence of osteonecrosis, clinically significant subchondral bone changes, insufficiency fracture, or accelerated joint space narrowing suggestive of chondrolysis,” the study authors reported. In addition, more than two-thirds of patients experienced a ≥50% analgesic response, measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)-A (pain) score, 4 weeks after the first and second injections. “Both injections resulted in similar improvements in OA symptoms across a broad spectrum of disease severity reflective of that seen in clinical practice,” the authors noted.

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Commenting on the study results, Andrew Spitzer, MD, Co-Director, Joint Replacement Program, Cedars-Sinai Orthopaedic Center and lead investigator said, “This valuable study suggests that repeat administration of Zilretta can provide patients suffering from knee OA consistent, substantial, and durable pain relief, and is generally well-tolerated. Importantly, analysis of the X-ray data showed no impact on cartilage or any other negative structural impact at one-year follow-up.” 

In December 2018, Flexion submitted for review the data on repeat administration to the FDA as part of a supplemental New Drug Application. The full study has been published in the journal Rheumatology and Therapy.

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