An evaluation of serum gentamicin concentrations and bacterial susceptibility to gentamicin in equine practice

Bactericidal and anti-biofilm effects of uncharged and cationic ultrasound-responsive nitric oxide microbubbles on Pseudomonas aeruginosa biofilms

Bacterial biofilms are a major and ongoing concern for public health, featuring both inherited genetic resistance traits and a conferred innate tolerance to traditional antibiotic therapies. Consequently, there is a growing need for novel methods of drug delivery, to increase the efficacy of antimicrobial agents. This research evaluated the anti-biofilm and bactericidal effects of ultrasound responsive gas-microbubbles (MBs) of either air or nitric oxide, using an in vitro Pseudomonas aeruginosa biofilm model grown in artificial wound medium. The four lipid-based MB formulations evaluated were room-air MBs (RAMBs) and nitric oxide MBs (NOMBs) with no electrical charge, as well as cationic (+) RAMBs⁺ and NOMBs⁺. Two principal treatment conditions were used: i) ultrasound stimulated MBs only, and ii) ultrasound stimulated MBs with a sub-inhibitory concentration (4 µg/mL) of the antibiotic gentamicin. The total treatment time was divided into a 60 second passive MB interaction period prior to 40 second ultrasound exposure; each MB formulation was tested in triplicate. Ultrasound stimulated RAMBs and NOMBs without antibiotic achieved reductions in biofilm biomass of 93.3% and 94.0%, respectively. Their bactericidal efficacy however was limited, with a reduction in culturable cells of 26.9% and 65.3%, respectively. NOMBs with sub-inhibitory antibiotic produced the most significant reduction in biofilm biomass, corresponding to a 99.9% (SD ± 5.21%); and a 99.9% (SD ± 0.07%) (3-log) reduction in culturable bacterial cells. Cationic MBs were initially manufactured to promote binding of MBs to negatively charged biofilms, but these formulations also demonstrated intrinsic bactericidal properties. In the absence of antibiotic, the bactericidal efficacy of RAMB⁺ and NOMB⁺ was greater that of uncharged counterparts, reducing culturable cells by 84.7% and 86.1% respectively; increasing to 99.8% when combined with antibiotic. This study thus demonstrates the anti-biofilm and bactericidal utility of ultrasound stimulated MBs, and specifically is the first to demonstrate the efficacy of a NOMB for the dispersal and potentiation of antibiotics against bacterial biofilms in vitro. Importantly the biofilm system and complex growth-medium were selected to recapitulate key morphological features of in vivo biofilms. The results us offer new insight for the development of new clinical treatments, for example, in chronic wounds.

Gentamicin-induced sensorineural auditory loss in healthy adult horses

Background

Irreversible sensorineural auditory loss has been reported in humans treated with aminoglycosides but not in horses.

Objective

Investigate if auditory loss occurs in horses treated using the recommended IV daily dosage of gentamicin for 7 consecutive days.

Animals

Ten healthy adult horses (7‐15 years; females and males, 5 each).

Methods

Prospective study. Physical and neurological examinations and renal function tests were performed. Gentamicin sulfate was administered at a dosage of 6.6 mg/kg via the jugular vein on alternating sides for 7 days. Gentamicin peak and trough concentrations were measured. Horses were sedated using detomidine hydrochloride IV to perform brainstem auditory evoked responses (BAER) before the first dose, immediately after the last dose, and 30 days after the last dose. Peaks latencies, amplitudes, and amplitude ratios were recorded. Data from the second and last BAER were compared to results at baseline. Bone conduction was performed to rule out conduction disorders.

Results

Seven horses had auditory loss: complete bilateral (N = 1), complete unilateral (N = 2), and partial unilateral (N = 4). Based on physical examination and BAER results, sensorineural auditory loss was suspected. Absent bone conduction ruled out a conduction disorder and further supported sensorineural auditory loss in horses with completely absent BAER. Auditory dysfunction was reversible in 4 of 7 horses.

Conclusions and Clinical Importance

Gentamicin at recommended doses may cause sensorineural auditory loss in horses that might be irreversible. Follow‐up studies are needed to investigate if other dosing protocols present a similar risk.

Gentamicin plasma concentrations in hospitalized horses and retrospective minimal inhibitory concentrations of gram-negative equine pathogens

OBJECTIVES

The optimal dosage regimen of gentamicin in horses is still under investigation. The objectives of this study were to determine gentamicin plasma concentrations in hospitalized horses treated with 10 mg/kg gentamicin (IV, q 24 h) and to determine whether a plasma concentration to minimum inhibitory concentration (MIC) ratio of 10:1 is reached for equine pathogens using this dose.

DESIGN

Prospective clinical observational study; retrospective study on MICs of 131 gram-negative bacteria isolated from horses (2012-2015).

SETTING

University teaching hospital.

ANIMALS

Ninety-eight horses >6 months old, treated with gentamicin for their primary disease, consecutive samples.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations were measured 1 hour (C_1h ) and 20 hours (C_20h ) after gentamicin administration using fluorescence polarization. Presence of systemic inflammatory response syndrome (SIRS) and azotemia was recorded, as well as the reason for antimicrobial administration (primary disease) and whether administration was prophylactic or therapeutic. The target C_1h of ≥20 µg/mL gentamicin was reached in 90% of horses and was sufficient to reach a plasma concentration:MIC of 10:1 in 32 of 131 (24%) of gram-negative aerobic bacteria. A C_20h ≤ 2 µg/mL was reached in 97% horses. Therapeutic versus prophylactic administration, primary disease, azotemia, and systemic inflammatory response syndrome were not associated with a failure to reach a desired peak or trough.

CONCLUSIONS

The gentamicin dose of 10 mg/kg every 24 hours should be further investigated and safety assessed because a target gentamicin plasma concentration of ≥20 µg/mL was achieved in the majority of cases. Nephrotoxic side effects were not assessed. Individual drug monitoring should be performed because clinical factors are unreliable predictors of plasma concentrations. A gentamicin target concentration of ≥40 µg/mL does not offer additional benefits compared to ≥20 µg/mL, due to the bimodal distribution of resistance in bacterial isolates.

Use of aminoglycoside antibiotics in equine clinical practice; a questionnaire-based study of current use

Veterinary use of the aminoglycoside antibiotics is under increasing scrutiny. This questionnaire-based study aimed to document the use of aminoglycosides with a particular focus on gentamicin. An online questionnaire was delivered to generalist equine veterinary surgeons and specialists in internal medicine to determine the perceived importance, frequency of use and routes of administration of the aminoglycoside antibiotics. A series of hypothetical scenarios were also evaluated regarding gentamicin. Data were compared to evaluate the impact of the level of specialisation on prescribing practices for different antibiotics using Chi-squared and Fischer's exact tests. Data were analysed from 111 responses. Gentamicin was commonly used empirically without culture and susceptibility testing. Generalists were more likely to use gentamicin only after susceptibility testing than specialists in a variety of clinical presentations including respiratory diseases, septic peritonitis, acute febrile diarrhoea, cellulitis and contaminated limb wounds (p < 0.01). Intravenous administration of gentamicin was most common, although inhaled and regional administration of gentamicin and amikacin were also described. Amikacin was most commonly used by intra-articular administration. Gentamicin was more likely to be used in high-risk procedures or contaminated surgeries (86% and 74%, respectively) compared with clean surgery (32%; p < 0.0001). Gentamicin was often used perioperatively in horses undergoing exploratory celiotomy and more commonly used in horses undergoing an enterotomy (90%) than without and enterotomy (79%; p = 0.04). Most respondents (86%) used gentamicin at a dose of 6.6 mg/kg in adults, with few changing their dosing strategies based on the presence of sepsis, although higher doses were more reported in foals (7-15 mg/kg) irrespective of the presence of sepsis. Aminoglycosides are widely used in equine practice and use outside current EU marketing authorisations is common. Stewardship of the aminoglycoside antibiotics could be enhanced in both generalists and specialists through the more frequent use of susceptibility testing, regional administration and dose adjustment, especially in foals.

Comparison of plasma and intra-articular gentamicin levels after intravenous administration in healthy horses

Septic arthritis is considered one of the most severe disorders that affect horses’ joints. Therapy is intended to eliminate the microorganisms that cause this infection. The intravenous administration of antibiotics is an easily performed technique, but there is no guarantee that the antibiotics will reach the joint milieu at high concentrations and remain elevated for a certain period of time. This study aimed to determine and compare the levels of gentamicin in the plasma and synovial fluid of healthy horses after intravenous administration for seven days. Five horses received 6.6 mg/kg intravenous gentamicin every 24 h for seven consecutive days. Blood and synovial fluid samples were collected from the right metacarpal-phalangeal joint before the start of the treatment (T0) and after 6 h (T6), 12 h (T12), and every 24 h during antibiotic therapy for seven days (D1 to D7). The levels of gentamicin in serum and synovial fluid were quantified by Enzyme-Linked Immunosorbent Assay (ELISA). The intravenous administration of 6.6 mg/kg of gentamicin, in horses, after a period of 24 h, promotes synovial fluid concentrations below the MIC of the drug, in spite of reaching high plasma concentrations of gentamicin, daily mean serum concentration which was 29-fold higher than the minimum inhibitory concentration (MIC) of the drug. The intravenous administration every 24 h during seven consecutive days did not cause systemic side effects, such as hepatic or renal injury.

Retrospective assessment of perioperative antimicrobial use for elective arthroscopy in horses

OBJECTIVE

To describe perioperative antimicrobial use in horses undergoing elective arthroscopy.

STUDY DESIGN

Retrospective study.

SAMPLE POPULATION

Horses that underwent elective arthroscopy at one institution between July 2016 and May 2018, excluding those with a suspected infectious orthopedic disease or with a comorbidity that may have impacted prophylactic antimicrobial use decisions.

METHODS

Medical records were reviewed to evaluate preoperative, intraoperative, and postoperative antimicrobial drug selection, dose, and timing. Associations between body weight and underdosing were evaluated by using analysis of variance, χ² test was used for categorical comparisons, and least squares fit was used to evaluate factors associated with duration of postoperative antimicrobials.

RESULTS

Among 150 horses, 149 (99.3%) received systemic preoperative antimicrobials. Only 53 (40.2%) horses were administered doses within 60 minutes of surgical incision. First incision was performed more than two half-lives after administration of sodium penicillin in 46 of 131 (35.1%) horses but in only 1 of 106 (0.8%) horses that received trimethoprim-sulfadoxine. Body weight was associated with underdosing for penicillin (P = .0075) and trimethoprim-sulfadoxine (P = .002) but not gentamicin (P = .92). Twenty-six (17%) horses received one postoperative antimicrobial dose, while antimicrobials were continued in hospital for a mean of 22.3 ± 4.4 hours after surgery in the other 123 horses. Among the 149 discharged horses, 115 (77.2%) were prescribed antimicrobials after discharge (range, 3-10 days; median, 3 days, interquartile range, 0 days).

CONCLUSION

Deviations from common recommendations were apparent and provide evidence for the requirement to develop interventions to optimize perioperative prophylaxis.

CLINICAL SIGNIFICANCE

Perioperative antimicrobial use practices should be regularly assessed to provide a benchmark and identify areas for intervention.

Antimicrobial susceptibility of bacterial isolates from ambulatory practice and from a referral hospital

BACKGROUND

Responsible use of antimicrobials in equine practice relies on knowledge of common bacterial isolates and their antimicrobial sensitivities.

OBJECTIVES

To assess the frequency of bacterial resistance to a combination of parenteral penicillin and gentamicin and to trimethoprim and sulfamethoxazole for PO use in a selection of clinical isolates, and subsequently to determine the prevalence of resistance to antimicrobials that might then be used as alternatives to first-line antimicrobials for the same isolates.

METHODS

Retrospective analysis of minimal inhibitory concentrations (MICs) of antimicrobials for 6354 bacterial isolates from 365 ambulatory practices and 519 isolates from a referral hospital. The MICs were used to indicate sensitivity or resistance to commonly used antimicrobials and the prevalences of resistance were compared between origin of the isolates, and among antimicrobial drugs.

RESULTS

Isolates from the referral hospital were significantly (P < .05) more likely to be resistant to the antimicrobials tested than those derived from ambulatory practice. Overall, 91% of the ambulatory isolates and 64% of the hospital isolates were sensitive to penicillin-gentamicin. For trimethoprim-sulfamethoxazole combination, 82% of the ambulatory practice isolates and 56% of the referral hospital isolates were sensitive.

CONCLUSIONS AND CLINICAL IMPORTANCE

Most isolates were sensitive to penicillin and gentamicin as well as trimethoprim-sulfamethoxazole. No predictable efficacious second choice antimicrobial was identified for those isolates resistant to the first-line antimicrobials. The likelihood of isolates being sensitive to second choice antimicrobials was variable but generally higher for ambulatory isolates compared to referral isolates. Bacterial identification and measurement of MIC are essential to make the appropriate antimicrobial choice.

Antimicrobial dosing for common equine drugs: a content review and practical advice for veterinarians in Australia

BACKGROUND

Appropriate dosing with antimicrobial agents is critical for effective treatment and to prevent the development of antimicrobial resistance.

METHODS

A review was undertaken of equine journal articles (Equine Veterinary Journal, Equine Veterinary Education, Australian Veterinary Journal, Australian Equine Veterinarian, Journal of Veterinary Internal Medicine and Journal of Equine Veterinary Science) between January 2015 and August 2018. Those with dosing regimens for procaine penicillin G, gentamicin or trimethoprim-sulfonamide in adult horses were examined and evaluated. Pharmacokinetics and -dynamics of these drugs were also reviewed.

RESULTS & CONCLUSION

The most frequently reported doses for penicillin, gentamicin and trimethoprim-sulfonamide were 20-25,000 IU/kg, 6.6 mg/kg and 30 mg/kg, respectively. Veterinarians treating equine patients in Australia should be aware of the current recommended doses and inter-dosing intervals to ensure efficacy in therapy and to preserve the usefulness of these antimicrobials for the future.

An evaluation of serum gentamicin concentrations and bacterial susceptibility to gentamicin in equine practice

Background

Therapeutic drug monitoring and minimum inhibitory concentration (MIC) data allow more informed use of gentamicin.

Hypothesis/Objectives

To measure peak and trough serum gentamicin concentrations in horses after a 6.6 mg/kg dose of gentamicin given IV and the MIC of gentamicin of bacteria for which gentamicin might be selected.

Methods

Retrospective analysis of hospital records. Peak and trough plasma gentamicin concentrations were measured after 6.6 mg/kg gentamicin IV in 339 hospitalized horses. The MIC of gentamicin was measured for 503 isolates from ambulatory practice and 33 from hospital practice. The distribution of gentamicin concentrations and MIC results were compared to current recommendations for MIC breakpoints.

Results

The median serum gentamicin concentration at 60 minutes after administration (C_60min) was 21.4 μg/mL with a distribution indicating that bacteria with MIC ≥2 μg/mL were unlikely to be exposed to sufficient gentamicin for effective killing. Approximately 90% of isolates from ambulatory practice and 36% of hospital isolates had MICs at or below breakpoints for susceptibility with most of the remainder unlikely to be responsive, even to higher IV doses.

Conclusions and Clinical Importance

Gentamicin at a dosage of 6.6 mg/kg IV is likely to be effective against the majority of infections encountered in ambulatory practice, but less effective in an equine hospital. Because there was a dichotomy of most bacteria as being clearly susceptible or clearly resistant to gentamicin, it appears unlikely that higher doses would have been more efficacious, especially in the hospitalized population in our study.