The stability and in vitro antibacterial efficacy of enrofloxacin and gentamicin solutions against Staphylococcus pseudintermedius over 28 days

Abstract

Background Many clinicians prepare compounded otic solutions to treat otitis externa (OE). Research evaluating the stability and antimicrobial efficacy of these solutions is limited. Hypothesis/Objectives This study determined the chemical stability and in vitro bactericidal efficacy of compounded solutions of enrofloxacin and gentamicin during storage for 28 days. Materials and methods Solutions of enrofloxacin (10 mg/mL, 1%) and gentamicin (3 mg/mL, 0.3%) were prepared with normal saline and 1 mg/mL dexamethasone. Solutions were stored at room temperature (25°C) for 0, 14 and 28 days. The chemical stability of the antibiotics and dexamethasone were determined using liquid chromatography tandem mass spectrometry in triplicate. Efficacy assessment was made with 10 isolates of Staphylococcus pseudintermedius obtained from dogs with OE. Serial 10‐fold dilutions of the bacteria with the compounded solutions were prepared and the colony count results were converted into colony‐forming units (cfus). The mean cfu/mL and cfu/mL reduction rates were compared between Day (D)0, D14 and D28. All of the antimicrobial testing solutions were performed in triplicate. Results Chromatography showed that both antibiotics and dexamethasone were stable for 28 days. No significant differences were observed in the antibiotic bactericidal efficacy of stored solutions at D0, D14 or D28. Conclusions and Clinical Relevance Solutions of 1% enrofloxacin and 0.3% gentamicin in normal saline with 0.1% dexamethasone maintained chemical stability and bactericidal efficacy over 28 days. These solutions can be considered as alternatives to commercial preparations for treatment of canine OE when indicated.

Stability Studies of the Dilution Series of Different Antibiotic Stock Solutions in Culture Medium Incubated at 37 °C

“…Metry et al confirmed enrofloxacin’s stability, with no significant changes over 28 days at room temperature [ 48 ]. Marx et al, Park et al, and Petritz et al conducted additional tests at room temperature, finding enrofloxacin stable over 7 days [ 32 ], 28 days [ 34 ], and 56 days [ 33 ], respectively.…”

“…Like florfenicol, enrofloxacin showed considerable stability, with 88.7% of the initial concentration detectable on average by day 12 in both UPW solution and concentrations diluted in TSB. Okerman et al found more than 90% of the initial concentration intact after six months at −20 [32], 28 days [34], and 56 days [33], respectively.…”

“…Literature reviews reveal that UPW solutions of enrofloxacin exhibit remarkable stability, maintaining their integrity at room temperature across various experiments, even in the presence of additional molecules, such as sweeteners and dexamethasone [ 32 , 33 , 34 ]. Similarly, the stability of florfenicol has predominantly been assessed under severe conditions, demonstrating robustness at elevated temperatures [ 35 , 36 ].…”

Antimicrobial Activity of Sempervivum tectorum L. Extract on Pathogenic Bacteria Isolated from Otitis Externa of Dogs

“…As indicated in the results of our study, the S. aureus clinical isolate was resistant to the most frequently used or first-line antibiotic prescribed for otitis externa infection (gentamicin). Thus topical and oral antibiotics (gentamicin and enrofloxacin) are frequently used in canine bacterial ear infections, and resistance is a significant concern [72]. An increasing antimicrobial resistance in the Staphylococcus spp.…”