Prolonged joint residency of triamcinolone acetonide after an intra-articular injection of FX006, a sustained release formulation for the treatment of osteoarthritis

Abstract

Purpose: Although available intra-articular (IA) corticosteroids are well established in the treatment of painful osteoarthritis (OA), limitations include short duration of pain relief (1-4 weeks), an effect consistent with the transient residency of these compounds in the joint and high plasma corticosteroid concentrations immediately following injection. FX006 is a novel IA sustained-release injectable formulation of 25% triamcinolone acetonide (TCA) in poly(lactic-co-glycolic acid) microspheres intended to prolong therapeutic concentrations of TCA in the joint and limit systemic exposure. In a previously described 6-week long clinical study, FX006 at 40 mg demonstrated maintenance of synovial concentrations of TCA consistent with pharmacologic activity for a period of at least 6 weeks, when levels of TCA produced by an equivalent dose of TCA IR were below the limit of quantitation. The current study extended these data on joint residency by measuring synovial fluid levels of TCA at later time points. Methods: In this multi-center, open-label study, patients with OA of the knee received a single IA injection of FX006 containing 10 or 40 mg TCA, or 40 mg of a standard, immediate-release suspension of TCA (TCA IR). A total of 50 patients were enrolled (FX006 10 mg: 10 patients, FX006 40 mg: 30 patients, TCA IR: 10 patients). Synovial fluid and plasma samples were obtained at baseline (pre-dose) and at the planned Final Visit at either Week 12, 16, or 20, depending on cohort assignment and availability of fluid in the knee. Concentrations of TCA were measured in plasma or in filtered synovial fluid samples using High Performance Liquid Chromatographic methods with Tandem Mass Spectrometry Detection and Automated Extraction, validated for the determination of TCA in human plasma and synovial fluid respectively. The quantitation limits of both assays were 50 to 50000 pg/mL. Results: In the FX006 10 mg group, 8 patients had synovial fluid available for analysis at Week 12. In the FX006 40 mg group, 6 patients had synovial fluid available for analysis at Week 12, 8 patients at Week 16 and 11 patients at Week 20. In the TCA IR group, 5 patients had synovial fluid available for analysis at Week 12. The concentrations of TCA achieved by 40 mg FX006 in the synovial fluid at Week 12 were 924 pg/mL, at Week 16, the IA concentrations of TCA were 224 pg/mL and by Week 20 they were below the lower limit of quantitation (Figure; geometric means from the earlier 6-week study and the current study are merged). The IA concentration of TCA in patients receiving 40 mg of TCA IR at Week 12 was below the lower limit of quantitation. FX006 maintained a gradient between synovial and systemic plasma concentrations of TCA for 16 weeks. Conclusions: A single IA administration of 40 mg of FX006 maintained pharmacologically active synovial fluid concentrations of TCA for at least 12 weeks, while TCA IR produced levels that are below the lower limit of quantitation by 6 weeks. These data underpin the differentiation of FX006 from TCA IR and provide pharmacokinetic basis for previously demonstrated prolongation and amplification of pain relief compared to TCA IR in OA patients following a single IA injection. FX006 also has the potential for an improved systemic safety profile as evidenced by peak plasma concentrations that are 40-fold lower than TCA IR at the same dose, seen in the aggregate of clinical studies with FX006 to date.