Long-lasting otic solution containing mometasone furoate can influence intradermal testing in dogs with healthy ears and otitis externa

Background: Topical therapy is preferred for otitis externa (OE) in dogs. Otic products commonly contain glucocorticoids that can be systemically absorbed and possibly interfere with diagnostic tests such as intradermal testing (IDT). Hypothesis/Objectives: To determine the effect of a long-lasting otic solution containing mometasone furoate (MF) on IDT immediate reactions and to determine withdrawal time before IDT. Animals: Seventeen dogs with healthy ears (Group 1) and 12 with OE (Group 2). Materials and Methods: Intradermal injections of histamine, anticanine-immunoglobulin (Ig)E and saline were subjectively and objectively evaluated before treatment and weekly for 6 weeks, after a single application of a long-lasting otic solution containing MF. Results: Statistically significant reductions in the mean subjective histamine scores after application of MF were observed at Weeks 1 (p = 0.012) and 2 (p = 0.028) in Group 1, and Weeks 1 (p = 0.00066), 2 (p = 0.02) and 4 (p = 0.034) in Group 2. Mean histamine objective scores were significantly reduced in Weeks 1 (p = 0.042), 2 (p = 0.0009), 3 (p = 0.001) and 5 (p = 0.018) in Group 1 only. The mean subjective anticanine-IgE scores were significantly reduced in Week 1 in both groups (p = 0.003, p = 0.0066), respectively. There were no significant changes in the mean anticanine-IgE objective score in either group. Conclusions and Clinical Relevance: Application of a long-lasting otic solution containing MF can interfere with IDT immediate reactions in healthy and OE dogs. Based on the subjective evaluation, IDT can be performed ≥2 weeks after application of the otic solution in healthy dogs, and ≥4 weeks in dogs with OE.