Preliminary study of the stability of dexamethasone when added to commercial veterinary ear cleaners over a 90 day period

Background: Topical corticosteroids are commonly used in the management of allergic otitis externa to diminish inflammation. A common strategy is to make compounded solutions of dexamethasone in ear cleaner. Hypothesis/Objectives: The objective of this study was to determine the stability of dexamethasone when added to four commercial ear cleaners (ec): designated ecA, ecB, ecC and ecD. Methods and Materials: Two concentrations (0.1 and 0.25 mg/mL) of dexamethasone were formulated for each cleaner solution from a 2 mg/mL solution and stored in the original manufacturers’ bottles at two temperatures: room (22 ˚C) and refrigerated (4 ˚C). Samples were evaluated in triplicate, using liquid chromatography-tandem mass spectrometry at 10 time points over 90 days. The mean and standard deviation were calculated for each time point. Results: A solution was considered stable if the dexamethasone value remained >90% of the target concentration. All dexamethasone solution values were stable to 90 days, except two solutions for ecA; the 0.25 mg/mL dexamethasone concentration was only stable to 14 (4 ˚C) and 21 days (22 ˚C). Conclusions and clinical importance: These results provide preliminary evidence in support of pharmaceutical stability data for dexamethasone when included in the above compounded solutions at the noted concentrations and temperatures.