Fosmidomycin for the Treatment of Canine Otitis Externa: A Randomised, Double-Blinded, Controlled 'Split Body' Clinical Trial.

Abstract

BACKGROUND: Targeted antimicrobial therapy for canine otitis externa (OE) represents an opportunity for antimicrobial stewardship. Fosmidomycin selectively inhibits the non-mevalonate pathway for isoprenoid biosynthesis utilised by canine-adapted, and not human-adapted, staphylococci. OBJECTIVES: To evaluate the safety and efficacy of fosmidomycin for treatment of bacterial OE compared with enrofloxacin. ANIMALS: Fifteen client-owned dogs with bilateral bacterial OE were enrolled. MATERIALS AND METHODS: Fosmidomycin stability in solution for 28 days was confirmed before trial commencement. A 'split body' design was used: each ear canal was randomised to receive a solution of fosmidomycin or enrofloxacin applied twice daily for 28 days, combined with a tapering anti-inflammatory course of oral prednisone. Owners and investigators were blinded to treatments. Dogs were evaluated at Day (D)0, D14 and D28 with clinical scores (0-3 otitis index score [OTIS3], ear cytological results, pain) and owner assessments (pruritus scores for each ear, quality-of-life scores and a hearing questionnaire). On D28, owners and investigators assessed global treatment efficacy for each ear. RESULTS: Treatment group did not significantly influence clinical scores; cytological scores, OTIS3 scores and pruritus scores significantly improved for both groups over the trial period. Treatment efficacy for both ears was assessed as good-to-excellent by owners and investigators for the majority of dogs. No safety concerns were identified. CONCLUSIONS AND CLINICAL RELEVANCE: Fosmidomycin and enrofloxacin performed comparably for topical treatment of bacterial otitis in this study. Fosmidomycin is a promising targeted antimicrobial for canine bacterial infections while limiting selection for antimicrobial resistance in human pathogens such as Staphylococcus aureus.