Dexamethasone-Antibiotic Interactions in Canine Ocular Bacteria: In Vitro Susceptibility Changes in Common Corneal Infection Pathogens

Objective: To investigate the impact of dexamethasone on the antibiotic susceptibility of common ocular pathogens in dogs and identify safe antibiotic-steroid combinations for veterinary ophthalmology.

Methods: This study utilized 30 bacterial isolates of Staphylococcus pseudintermedius, Streptococcus canis, and Pseudomonas aeruginosa, collected from canine patients with suspected bacterial keratitis. The isolates were tested against 17 antibiotics in the presence of dexamethasone concentrations ranging from 0 to 2 mg/mL. Minimum inhibitory concentrations (MICs) were determined using standardized broth microdilution techniques, and changes in susceptibility were analyzed statistically.

Results: Dexamethasone administration resulted in a significant increase in resistance for ciprofloxacin, ticarcillin, tobramycin, and ceftiofur in S. pseudintermedius; ticarcillin in S. canis; and ciprofloxacin and moxifloxacin in P. aeruginosa. Despite these increases, amikacin and cefazolin showed minimal impact on resistance when combined with dexamethasone, indicating their potential for safe use in combination therapies.

Conclusion: The findings highlight the potential for dexamethasone to alter antibiotic susceptibility in canine ocular pathogens. While dexamethasone can increase resistance in certain antibiotics, amikacin and cefazolin appear to be safer options for combination therapy.