Determination of enrofloxacin stability and in vitro efficacy against Staphylococcus pseudintermedius and Pseudomonas aeruginosa in four ear cleaner solutions over a 28 day period

Exposure to blue light reduces antimicrobial resistant Pseudomonas aeruginosa isolated from dog ear infections

Introduction

Pseudomonas aeruginosa is a leading cause of canine otitis externa. Enrofloxacin is often applied topically to treat this condition, although recalcitrant and recurring infections are common. There is evidence that exposure to blue light (400-470 nm) has a bactericidal effect on P. aeruginosa and other microorganisms.

Methods

In the present study, we tested the biocidal effect of blue light (375-450 nm), alone or in combination with enrofloxacin, against six isolates of P. aeruginosa from dogs with otitis externa (5 of which were resistant to enrofloxacin).

Results

Treatment of planktonic cell cultures with blue light resulted in significant (p < 0.5) reductions in Colony Forming Units (CFU) for all seven strains tested, in some cases below the limit of detection. The greatest bactericidal effect was observed following exposure to light at 405 nm wavelength (p < 0.05). Exposure to blue light for 20 min usually resulted in a greater reduction in Pseudomonas aeruginosa than enrofloxacin treatment, and combination treatment typically resulted in the largest reductions in CFU. Analysis of the genome sequences of these strains established that enrofloxacin resistance was likely the result of a S466F substitution in GyrB. However, there was no clear association between genotype and susceptibility to blue light treatment.

Discussion

These results suggest that blue light treatment, particularly at 405 nm wavelength, and especially in combination with enrofloxacin therapy, could be an effective treatment for otherwise recalcitrant canine otitis externa caused by Pseudomonas aeruginosa. It may also provide a way of extending the usefulness of enrofloxacin therapy which would otherwise be ineffective as a sole therapeutic agent.

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

The long-term stability of antibiotics in culture media remains underexplored in scientific literature. This study evaluated the stability of eight distinct antibiotic stock solutions-amoxicillin, cefotaxime, neomycin, oxytetracycline, florfenicol, enrofloxacin, colistin, and potentiated sulfonamide-and their 10-fold dilution series in tryptone soy broth (TSB) at 37 °C, over 12 days. Samples were collected immediately after preparation and on days 1, 2, 5, 7, 9, and 12, with active substance concentrations measured using ultra-high-performance liquid chromatography (UHPLC) coupled with mass spectrometry. The results indicated that among the ultrapure water stock solutions, neomycin, florfenicol, and potentiated sulfonamide maintained stability (>95%). Within the culture medium, florfenicol showed consistent stability (100%) throughout the study, potentiated sulfonamide experienced minor degradation (>85%), and neomycin underwent significant degradation. Amoxicillin, oxytetracycline, and colistin displayed considerable degradation in both solution types but were more stable in ultrapure water solutions. The stability of cefotaxime and enrofloxacin in ultrapure water solutions and in the medium was very similar when compared; however, 3.6% of the former and 88.7% of the latter remained detectable by day 12. These findings are crucial for minimum inhibitory concentration (MIC) assessments, especially in minimum bactericidal concentration (MBC) studies, and in experiments concerning long-term evolution and co-selection. This study underscores the necessity of stability assessments in culture media to validate future experimental outcomes.

Pseudomonas spp. in Canine Otitis Externa

Canine otitis externa (OE) is a commonly diagnosed condition seen in veterinary practice worldwide. In this review, we discuss the mechanisms of the disease, with a particular focus on the biological characteristics of Pseudomonas aeruginosa and the impact that antibiotic resistance has on successful recovery from OE. We also consider potential alternatives to antimicrobial chemotherapy for the treatment of recalcitrant infections. P. aeruginosa is not a typical constituent of the canine ear microbiota, but is frequently isolated from cases of chronic OE, and the nature of this pathogen often makes treatment difficult. Biofilm formation is identified in 40-95% of P. aeruginosa from cases of OE and intrinsic and acquired antibiotic resistance, especially resistance to clinically important antibiotics, highlights the need for alternative treatments. The role of other virulence factors in OE remains relatively unexplored and further work is needed. The studies described in this work highlight several potential alternative treatments, including the use of bacteriophages. This review provides a summary of the aetiology of OE with particular reference to the dysbiosis that leads to colonisation by P. aeruginosa and highlights the need for novel treatments for the future management of P. aeruginosa otitis.

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

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.

Determination of amikacin stability at 1% and 3% concentrations in four topical solutions over a 56 day period

BACKGROUND

Anecdotally, amikacin has been added to compounded topical preparations for the management of canine bacterial otitis externa. However, the stability of amikacin within these solutions is unknown.

HYPOTHESIS/OBJECTIVES

The purpose of this study was to determine the stability of amikacin at 10 and 30 mg/mL concentrations in four topical solutions over a 56 day period. We hypothesised that amikacin would maintain chemical stability within the various solutions.

METHODS AND MATERIALS

Amikacin was formulated to 10 and 30 mg/mL (1% and 3%) concentrations within four topical solutions: tris-EDTA (TrizEDTA Aqueous Flush) (TE); 0.15% chlorhexidine gluconate and tris-EDTA (TrizCHLOR Flush) (TC); 0.9% NaCl (NA); and 0.9% NaCl + 2 mg/mL dexamethasone (ND). Samples were made in duplicate and stored at room temperature (25°C) for 0, 7,14, 21, 28 and 56 days. Amikacin content was quantified, in triplicate, by ultrahigh-performance liquid chromatography tandem mass spectrometry.

RESULTS

The recovered amikacin concentrations for the 10 mg/mL solutions ranged from 10 to 13.5 mg/mL (mean 11.5 mg/mL) with the exception of NA sample 2 at Day (D)0 (9.4 mg/mL) and D7 (9.2 mg/mL). The recovered amikacin concentrations for the 30 mg/mL solutions ranged from 30 to 40.2 mg/mL (mean 35.7 mg/mL). No significant difference was seen between the amikacin concentrations at D0 compared to D56 for all solutions except 10 mg/mL TE (P < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

Amikacin maintained stability within TE, TC, NA and ND over 56 days except when formulated at 10 mg/mL within TE.

Chemical and microbiological stability of diluted ceftazidime in three different solutions under three storage temperatures over a 28 day period

BACKGROUND

Ceftazidime (CAZ) solutions are being used based on anecdotal reports for otitis externa complicated by multidrug-resistant Pseudomonas aeruginosa (MDR PA). The chemical and microbiological stability of these proposed compounded solutions have not been evaluated, and likely are affected by the diluent and storage duration or temperature.

HYPOTHESIS/OBJECTIVES

Compounded CAZ solutions would show variable degradation dependent on diluent, time and temperature. The antimicrobial activity of the solutions would reflect changes in concentration and not alterations to the chemical compound.

METHODS AND MATERIALS

Ceftazidime was compounded with 100 mL 0.9% sodium chloride (NA+CAZ), 118 mL Triz-EDTA Aqueous flush (TE+CAZ) and 125 mL Douxo Micellar Solution (MI+CAZ). Aliquots of the solutions were stored at 25ºC, 4ºC and -20ºC for 28 days. High-performance liquid chromatography was used to analyse CAZ recovery from compounded solutions at weekly intervals. A modified broth dilution technique was utilised to assess minimum inhibitory concentration (MIC) to monitor antimicrobial activity against a reference PA strain.

RESULTS

Temperature, duration of storage and diluent each had independent effects on the chemical stability of CAZ. CAZ concentrations decreased over time as well as with increased temperature. NA+CAZ solutions exhibited the least degradation compared to the other solutions. The MIC for PA was most consistent for NA+CAZ solutions regardless of storage temperature and duration of storage.

CONCLUSIONS AND CLINICAL IMPORTANCE

Chemical and microbiological stability of compounded CAZ solutions varied by diluent, storage temperature and duration of storage. Dilution in NA resulted in the lowest variation in stability over 28 days when stored at refrigerated or frozen temperatures compared to other diluents.

Preliminary study of the stability of dexamethasone when added to commercial veterinary ear cleaners over a 90 day period

BACKGROUND

Topical corticosteroids are commonly used in the management of allergic otitis externa to diminish inflammation. A common strategy is to make compounded solutions of dexamethasone in ear cleaner.

HYPOTHESIS/OBJECTIVES

The objective of this study was to determine the stability of dexamethasone when added to four commercial ear cleaners (ec): designated ecA, ecB, ecC and ecD.

METHODS AND MATERIALS

Two concentrations (0.1 and 0.25 mg/mL) of dexamethasone were formulated for each cleaner solution from a 2 mg/mL solution and stored in the original manufacturers' bottles at two temperatures: room (22 ˚C) and refrigerated (4 ˚C). Samples were evaluated in triplicate, using liquid chromatography-tandem mass spectrometry at 10 time points over 90 days. The mean and standard deviation were calculated for each time point.

RESULTS

A solution was considered stable if the dexamethasone value remained >90% of the target concentration. All dexamethasone solution values were stable to 90 days, except two solutions for ecA; the 0.25 mg/mL dexamethasone concentration was only stable to 14 (4 ˚C) and 21 days (22 ˚C).

CONCLUSIONS AND CLINICAL IMPORTANCE

These results provide preliminary evidence in support of pharmaceutical stability data for dexamethasone when included in the above compounded solutions at the noted concentrations and temperatures.

Highly efficient activation of peroxymonosulfate by cobalt sulfide hollow nanospheres for fast ciprofloxacin degradation

We reported a facile preparation of CoS₂, Co₃S₄, and Co₉S₈ hollow nanospheres (HNSs) and their use as peroxymonosulfate (PMS) activators for ciprofloxacin (CIP) degradation. The CIP degradation efficiency follows the order of CoS₂ > Co₃S₄ > Co₉S₈. The Co²⁺ is proved to be active site for PMS activation and reactive oxygen species generation. The effect of operating parameters on performance of CoS₂ HNSs/PMS system was explored. CoS₂ HNSs exhibited highly catalytic activity in a wide pH range of 3 - 10. Complete removal of 10 mg/L CIP was achieved by CoS₂ HNSs in 3 min at initial pH of 8.0 with 62.6% CIP mineralization. Three other organic pollutants (rhodamine B, methylene blue and tetracycline) were also degraded to evaluate the universality of the CoS₂ HNSs/PMS system. The catalytic performance dropped in the presence of chloride, phosphate, nitrate ions and humic acid. Above 97% CIP removal was achieved even in the sixth run. The degradation pathway of CIP was proposed based on HPLC-MS/MS analysis of CIP intermediates, and two new intermediates, namely, C₁₅H₁₈O₄N₃F (m/z 323) and C₂₉H₃₁O₄N₆F (m/z 546), were identified for the first time. Both OH and SO₄^- were generated and the latter played a key role in CIP degradation.

Topical ear treatment - options, indications and limitations of current therapy

Topical otic products form an integral part of the overall management of otitis externa. With an ever increasing array of ear drops and cleaners to choose from, appropriate selection of therapy can be difficult. The investigation of all cases of otitis externa should consider primary and secondary causes and predisposing and perpetuating factors. This article considers topical therapy under these same broad headings and discusses, through literature review, the various properties of the components of the ear cleaning solutions and drops.

Stability of three commonly compounded extemporaneous enrofloxacin suspensions for oral administration to exotic animals

OBJECTIVE

To evaluate the stability of 3 extemporaneous oral suspensions of enrofloxacin mixed with readily available flavoring vehicles when stored at room temperature (approx 22°C).

DESIGN

Evaluation study.

SAMPLES

3 commonly compounded oral suspensions of enrofloxacin.

PROCEDURES

On day 0, commercially available enrofloxacin tablets were compounded with a mixture of distilled water and corn syrup (formulation A) or cherry syrup (formulation B) flavoring vehicles to create suspensions with a nominal enrofloxacin concentration of 22.95 mg/mL, and 2.27% enrofloxacin injectable solution was compounded with a liquid sweetener (formulation C) to create a suspension with a nominal enrofloxacin concentration of 11.35 mg/mL. Preparations were stored in amber-colored vials at room temperature for 56 days. For each preparation, the enrofloxacin concentration was evaluated with high-performance liquid chromatography at prespecified intervals during the study. The pH, odor, and consistency for all suspensions were recorded at the start and completion of the study.

RESULTS

Relative to the nominal enrofloxacin concentration, the enrofloxacin concentration strength ranged from 95.80% to 100.69% for formulation A, 108.44% to 111.06% for formulation B, and 100.99% to 103.28% for formulation C. A mild pH increase was detected in all 3 suspensions during the study.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that, when stored in amber-colored vials at room temperature for 56 days, the enrofloxacin concentration strength in all 3 formulations was retained within acceptance criteria of 90% to 110%. Subjectively, cherry syrup flavoring was better at masking the smell and taste of enrofloxacin than were the other mixing vehicles.