Stability of Ketamine-Xylazine-Butorphanol formulation to establish an evidence-based beyond-use date

Background A combination injection formulation containing 8.3 % w/v ketamine (K), 0.83 % w/v xylazine (X), and 0.083 % w/v butorphanol (B) is frequently used for sedation and anesthesia in New World Camelids. In this study, we aimed to evaluate the chemical and microbiological stability of this compounded formulation, providing scientific support for its use beyond the current 28-day beyond-use date (BUD) as outlined in the current USP ' 797 ' guidance. Methods A sterile KXB formulation was aseptically prepared, consisting of 8.3 % w/v K, 0.83 % w/v X, and 0.083 % w/v B using the individual injections of each drug (K, X, B) filled into sterile 20 mL glass vials. A validated, stability-indicating HPLC method was developed to simultaneously quantify each drug in the injection formulation. The samples were stored at room temperature (∼23 °C) and at 40 °C and analyzed at 0.5, 1, 1.5, 2, and 3 months for physical and chemical stability. Microbiological stability was assessed to detect potential microbial growth over a 45-day period. Results The developed HPLC assay was precise, accurate, and stability-indicating for each drug in the injection. The formulation remained clear and within pH 4.1–4.3 throughout the study. Drug assay values remained within 90–110 % after three months of storage at room temperature and at 40 °C. No microbial growth was observed up to and beyond 28 days, in compliance with USP guidelines. Conclusion The validated HPLC method confirmed the KXB formulation demonstrated chemical stability for at least three months and maintained microbial stability up to and beyond a 28-day period, supporting an evidence-based beyond-use date of this multi-drug formulation.