Otic steroids are commonplace in management of dogs with atopy and allergic otitis externa and it has been shown that glucocorticosteroids could suppress adrenal function and also affect intradermal skin testing (IDT). In a blinded, placebo-controlled, crossover study, serum chemistry panels, ACTH stimulation tests, and limited IDT were performed on 16 normal dogs treated with placebo or otic betamethasone (Otomax) at the manufacturer's recommended twice-daily dosage. Dogs were treated for 14 days, and there was a 4-week washout period before treatments were switched. There was no difference between pre- and posttreatment complete blood counts or ACTH stimulation tests. Although serum alkaline phosphatase levels were significantly elevated after treatment, they remained within normal range. There was no difference in the results of the pretreatment intradermal test results in the 2 groups of dogs, indicating that a 4-week washout period was adequate. In contrast, a significant difference in histamine and house dust reactions was found after 14 days of treatment.

COMMENTARY: It is important to note that this study was done in dogs with healthy ears, and investigators controlled the amount of medication. Ears with clinical disease may have increased absorption of otic preparations. Also, owners may instill more of the medication than recommended by the manufacturer. This study showed no adrenal suppression and only mild increases in liver enzymes; however, results in dogs with clinical disease may differ. When counseling clients regarding withdrawal periods, therapy with betamethasone-containing products should be tapered over a period of at least 4 weeks. -- Karen A. Moriello, DVM, Diplomate ACVD

Effects of otic betamethasone on intradermal testing in normal dogs. Ginel PJ, Garrido C, Lucena R. VET DERMATOL 18:205-210, 2007.