Stability of Dexamethasone When Added to Commercial Ear Cleaners

In the Literature

Emery CB, Outerbridge CA, Knych HK, Lam ATH, Gomez-Vazquez JP, White SD. Preliminary study of the stability of dexamethasone when added to commercial veterinary ear cleaners over a 90 day period. Vet Dermatol. 2021;32(2):168-e39.

The Research …

Chronic allergic otitis externa requires both short- and long-term treatment plans. In short-term plans, any active infections and inflammation need to be resolved; dozens of commercial products are available for this purpose. In long-term plans, inflammation and infection must be prevented to avoid flares of disease; however, few commercial products are available in this capacity. Because of this, many clinicians make their own solutions by adding a steroid to a commercial ear-flush product; however, few data exist regarding the long-term stability of such solutions.

This study investigated the stability of dexamethasone (2 mg/mL) added to 4 different commercial ear flushes (ie, Tris-EDTA + ketoconazole, Tris-EDTA + ketoconazole + chlorhexidine gluconate, salicylic acid, and phytosphingosine) at different concentrations (0.1 mg/mL and 0.25 mg/mL). Solutions were stored in their original bottles and tested at room temperature (71.6°F [22°C]) and when refrigerated (39.2°F [4°C]). 

Stability was measured using mass spectrometry at 10 time points over 90 days. The solution was considered stable if the dexamethasone concentration remained >90% of the starting concentration. All solutions were stable at 90 days, except Tris-EDTA + ketoconazole with 0.25 mg/mL dexamethasone, which was only stable up to 14 days at the refrigerated temperature and up to 21 days at room temperature.

… The Takeaways

Key pearls to put into practice:

• Veterinary dermatologists frequently use topical corticosteroids to manage allergic otitis externa; however, there is a scarcity of commercial therapeutic products that contain a corticosteroid without added antibiotics. Many over-the-counter products contain hydrocortisone, which, as a weak steroid, may not be adequate for severe cases of otitis. Clinicians can instead consider making their own steroid-containing ear flushes using injectable dexamethasone that can be applied regularly to the ears to prevent flares of allergic otitis. Frequency (eg, daily to weekly) varies based on severity of disease.

• Prevention of otitis flares is important to limit chronic pathologic changes (eg, fibrosis, calcification) to the ear canal, as these severe changes result in the need for surgical ablation in order to resolve the chronic ear disease.

• In this study, dexamethasone (2 mg/mL) was added to commercial ear products. Although a 4 mg/mL product is also available and may be stable when added to commercial flushes, further testing and peer-reviewed studies on long-term safety and efficacy are needed.