The effect of otic vehicle and concentration of dexamethasone on liver enzyme activities and adrenal function in small breed healthy dogs

Dexamethasone 0.1% in propylene glycol vehicle has been shown to cause adrenal suppression and increased liver enzyme concentrations in normal dogs. The objectives of this study were to determine if these effects are concentration or vehicle dependent and to evaluate a dexamethasone 0.01% solution. Twenty-one privately owned normal dogs were included in this double-blinded study. Chemistry panels and adrenocorticotropin hormone (ACTH) stimulation tests were performed on day 0 and 15. Dogs were randomly assigned treatment with dexamethasone 0.01% in saline, 0.1% in saline, or 0.1% in a commercial preparation (Tresaderm®: Merial, Duluth, GA, USA) in each ear twice daily for 2 weeks. Nineteen dogs completed the study. After 2 weeks of treatment, all dogs receiving dexamethasone 0.01% in saline had normal ACTH stimulation tests and liver enzyme values. In contrast, four of seven dogs (57.14%) receiving dexamethasone 0.1% in saline experienced adrenal suppression, and four of six dogs (66.67%) receiving Tresaderm® experienced adrenal suppression with three of those dogs (50%) experiencing marked adrenal suppression. No dogs receiving dexamethasone 0.1% in saline had increased liver enzyme concentration, while one of six dogs (16.67%) experienced a slight elevation in alkaline phosphatase. In conclusion, it appears that adrenal suppression caused by otic dexamethasone is concentration and perhaps vehicle dependent. Veterinarians who formulate dexamethasone 0.1% otic solutions should be cognizant of potential adrenal suppression similar to that seen with Tresaderm® although not to the same degree. Dexamethasone at 0.01% did not cause adrenal suppression or liver enzyme alterations after 2 weeks of treatment.