In vitro and in vivo evaluation of a potentiated miconazole aural solution in chronic Malassezia otitis externa in dogs

This study assessed the in vitro and in vivo activity of an ear solution containing a third-generation chelating agent (Tricide®) as an antimicrobial potentiator for miconazole in chronic Malassezia otitis. Thirty-one ears from 20 dogs were enrolled in the study. Fungal culture, minimum inhibitory concentration (MIC), and minimum fungicidal concentration (MFC) testing of miconazole with and without Tricide® were performed on all ears. In a randomized, controlled, and blinded treatment trial the ears were treated either with 0.9% saline solution containing 0.01% miconazole, 0.03% dexamethasone and 540 μg/mL Tricide® or the same solution without Tricide®. Cytologic and auroscopic examinations were conducted on day 0, 14 and 28 and evaluated for number of yeast organisms, degree of erythema, hyperplasia and amount of discharge. The in vitro data was compared with Wilcoxon signed-rank test. The cytologic and auroscopic scores were compared between the visits and treatment groups at day 0, 14 and 28 using a Wilcoxon-Mann-Whitney test and repeated measures analysis. MIC and MFC were significantly (P < 0.0001) reduced when miconazole was combined with the chelating agent versus miconazole alone. The cytologic scores were significantly lower on days 14 (P = 0.0156) and 28 (P = 0.0280) for the group treated with Tricide®. The auroscopic scores decreased significantly by the end of the trial compared to day 0, but the difference between the two groups was not significant. This study suggests that Tricide® enhances in vitro activity and in vivo efficacy against Malassezia sp. in dogs with yeast otitis.