Tolerability of Otic Solutions Containing Different Enrofloxacin Concentrations in Dogs with Healthy Ears

Otitis externa (OE) is a common disease in dogs, and topical medications are the preferred treatment. Compounded solutions of enrofloxacin are commonly used in practice to treat bacterial OE; however, the tolerability of different concentrations of this antibiotic in the ear canals of dogs has not been evaluated. The objective of this study is to determine if a higher concentration of enrofloxacin applied to the external ear canal is clinically tolerated in dogs with healthy ears. Sixteen client-owned dogs with bilateral healthy ears and no previous history of OE were enrolled. Injectable enrofloxacin 2.27% diluted with sterile sodium chloride in 1:1 (11.35 mg/mL) and 2:1 (15 mg/mL) ratios were applied into the dogs' right and left ears, respectively, q 12 hr for 14 days. Based on video otoscopic examination, clinical score for canine OE (OTIS3) results before application were ≤1 for all dogs. During the study and at the conclusion, all scores remained ≤2, which is considered normal. No cytologic inflammatory cells were seen in any of the dogs' ears throughout the study. Different concentrations of enrofloxacin solution applied topically were well tolerated by dogs with healthy ears and can be considered for the treatment of dogs with bacterial OE.