The concurrent use of 2.5% polyacrylamide hydrogel and betamethasone esters for intra-articular injection is well tolerated in 10 healthy horses.

Objective: This study assessed the safety and tolerability of concurrent intra-articular (IA) injection of 2.5% polyacrylamide hydrogel (2.5% iPAAG) and betamethasone sodium phosphate and betamethasone acetate esters (BME) in the metacarpophalangeal joints (MCPJs) of healthy horses.

Methods: 10 healthy therapeutic riding horses were enrolled in this open-label safety study from August 1 to September 14, 2023. Inclusion criteria required normal physical examinations, insulin level, hematology, biochemistry, soundness at all gaits, and negative forelimb flexion tests. Screening occurred from days -14 to -0. Each horse received a single IA injection of 1 mL of 2.5% iPAAG and 1 mL of BME (6 mg/mL) into the right MCPJ on day 0. Posttreatment veterinary assessments (days 0, 1, 2, 3, 7, 14, and 30) included physical examinations, joint-specific evaluations (skin temperature, fetlock circumference at the level of the MCPJ), soundness assessments, and adverse event monitoring. Caretaker observation diaries (days 0 through 30) were also reviewed.

Results: No adverse events occurred, and all horses remained clinically sound. Joint circumference remained stable without evidence of effusion. Transient increases in skin temperature on days 2, 3, 7, and 14 correlated with ambient temperature changes, returning to baseline by day 30. Caretaker observations supported clinical findings.

Conclusions: Concurrent IA administration of 2.5% iPAAG and BME was safe and well tolerated in the right MCPJ of healthy horses, with no evidence of local or systemic adverse effects.

Clinical relevance: This therapy combines BME's short-term anti-inflammatory effects with 2.5% iPAAG's long-term synovial integration, warranting further evaluation in diseased joints.