Drug distribution and stability in extemporaneous preparations of meloxicam and carprofen after dilution and suspension at two storage temperatures

Objective - To determine dispersion uniformity and stability of meloxicam and carprofen in extemporaneous preparations stored for 28 days. Design - Prospective study. Sample Population - Meloxicam and carprofen (commercial formulations) were compounded (day 0) with deionized water (DW), 1% methylcellulose gel (MCG), MCG and simple syrup (SS; 1:1 mixture), or a suspending and flavoring vehicle combination (SFVC; 1:1 mixture) to nominal drug concentrations of 0.25, 0.5, or 1.0 mg/mL and 1.25, 2.5, or 5.0 mg/mL, respectively. Procedures - Preparations were stored at approximately 4°C (39.2°F) or 22°C (71.6°F). For each preparation, drug concentrations were determined and drug stability was evaluated at intervals during storage; on days 0 and 28, pH values were measured and bacterial cultures were initiated. Results - In meloxicam-DW, meloxicam-MCG (0.25 mg/mL), and meloxicam-MCG (0.5 mg/mL) preparations, drug distribution was uniform (coefficient of variation < 10%); > 90% of the original drug concentration was maintained for 28 days. Despite uniform drug distribution of the carprofen-SFVC preparations, most retained ≥ 90% of the original drug concentration for only 21 days. Use of the MCG-SS combination resulted in foamy preparations of unacceptable variability. After 28 days, pH decreased slightly in meloxicam-DW and meloxicam-MCG preparations (0.17 ± 0.04 and 0.21 ± 0.04, respectively). Carprofen-SFVC (2.5 mg/mL) and carprofen-MCG-SS (5.0 mg/mL) preparations stored at 22°C for 28 days yielded bacterial growth. Conclusions and Clinical Relevance - DW, MCG, and the SFVC can be used successfully for extemporaneous preparation of meloxicam and carprofen for administration to small exotic animals. Refrigeration is recommended for preparations of meloxicam-DW and carprofen-SFVC.