ZILRETTA is formulated in 75:25 poly(lactic-co-glycolic acid) (PLGA) microspheres with a nominal drug load of 25% (w/w) and is provided as a sterile white to off-white powder. ZILRETTA is prepared with a supplied diluent containing an isotonic, sterile, aqueous solution of sodium chloride (NaCl; 0.9% w/w), sodium carboxymethylcellulose (CMC; 0.5% w/w) and polysorbate-80 (0.1% w/w) to form a 5 mL sterile suspension intended for intra-articular injection. 

Active Ingredient 

The chemical name for triamcinolone acetonide is 9-fluoro-11β,16α,17,21-tetrahydroxypregna-1,4-diene- 3,20-dione cyclic 16,17-acetal with acetone. Its structural formula is: 

Structural Formula 

MW 434.50 with a molecular formula of C 24H 31FO 6 

Triamcinolone acetonide occurs as a white to almost white, crystalline powder having not more than a slight odor and is practically insoluble in water and very soluble in alcohol. Each vial of ZILRETTA powder contains 40 mg of triamcinolone acetonide in 160 mg of microspheres, resulting in 32 mg of deliverable triamcinolone acetonide when prepared according to the Instructions for Use.  

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action 

Triamcinolone acetonide is a corticosteroid with anti-inflammatory and immunomodulating properties. It binds to and activates the glucocorticoid receptor, leading to activation of anti-inflammatory transcription factors such as lipocortins and inhibition of inflammatory transduction pathways by blocking the release of arachidonic acid and preventing the synthesis of prostaglandins and leukotrienes. 

12.2 Pharmacodynamics 

Studies indicate that following a single intramuscular dose of 60 to 100 mg of immediate-release triamcinolone acetonide injectable suspension, adrenal suppression occurs within 24 to 48 hours and then gradually returns to normal, usually in 30 to 40 days. To assess potential effects of the systemic levels of triamcinolone acetonide associated with a single intra-articular (IA) administration of ZILRETTA on hypothalamic pituitary adrenal (HPA) axis function, serum and urine cortisol levels were monitored over 6 weeks post injection. Adrenal suppression with ZILRETTA occurred within 12-24 hours and then gradually returned to normal, within 30-42 days. 

Corticosteroids may increase blood glucose concentrations. 

In a study where 18 patients with osteoarthritis knee pain and controlled type 2 diabetes mellitus received a single IA injection of ZILRETTA into the knee, the change from baseline in average blood glucose over the 72 hours after injection as measured by a continuous glucose monitoring device was 8.2 mg/dL (95% confidence interval 0.1, 29.2). 

12.3 Pharmacokinetics 

ZILRETTA is an extended-release dosage form consisting of microspheres of poly(lactic-co-glycolic acid) (PLGA) containing triamcinolone acetonide. Plasma pharmacokinetic parameters for triamcinolone acetonide following IA administration of ZILRETTA or 40 mg immediate-release triamcinolone acetonide into the knee are provided in Table 4.