Sustained intra-articular release of celecoxib from in situ forming gels made of acetyl-capped PCLA-PEG-PCLA triblock copolymers in horses.

In this study, the intra-articular tolerability and suitability for local and sustained release of an in situ forming gel composed of an acetyl-capped poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) copolymer loaded with celecoxib was investigated in horse joints. The systems were loaded with two dosages of celecoxib, 50 mg/g ('low CLB gel') and 260 mg/g ('high CLB gel'). Subsequently, they were injected into the joints of five healthy horses. For 72 h after intra-articular injection, they induced a transient inflammatory response, which was also observed after application of Hyonate(®), a commercial formulation containing hyaluronic acid for the intra-articular treatment of synovitis in horses. However, only after administration of the 'high CLB gel' the horses showed signs of discomfort (lameness score: 1.6 ± 1.3 on a 5-point scale) 1 day after injection, which completely disappeared 3 days after injection. Importantly, there was no indication of cartilage damage. Celecoxib Cmax in the joints was reached at 8 h and 24 h after administration of the 'low CLB gel' and 'high CLB gel', respectively. In the joints, concentrations of celecoxib were detected 4 weeks post administration. Celecoxib was also detected in plasma at concentrations of 150 ng/ml at day 3 post administration and thereafter its concentration dropped below the detection limit. These results show that the systems were well tolerated after intra-articular administration and showed local and sustained release of celecoxib for 4 weeks with low and short systemic exposure to the drug, demonstrating that these injectable in situ forming hydrogels are promising vehicles for intra-articular drug delivery.