Ceftiofur use and antimicrobial stewardship in the horse

Equine practitioners require recommendations that support antimicrobial stewardship and avoid generating resistance to medically important antibiotics. This review examines current inadequacies in antimicrobial stewardship standards within the veterinary community, related to antimicrobial categorisation and prescribing practices. Resistance to cephalosporin antibiotics in horses is also described. Properties of cephalosporin antibiotics are outlined and equine-specific studies of ceftiofur, a third-generation cephalosporin antibiotic with medical importance, are detailed. Readers are provided with recommendations that encourage appropriate use of ceftiofur, citing the evidence available in horses.

Concentration of cephalothin in body fluids and tissue samples of Thoroughbred horses

Cephalothin (CET) concentrations in body fluids (plasma, synovial fluid, pleural fluid, peritoneal fluid, and aqueous humor) and tissue samples (bone, lung, jejunum, hoof, and subcutaneous tissue) were investigated to consider the treatment of infectious diseases in horses. CET 22 mg/kg body weight was intravenously administered to 12 horses. Samples were collected from four different horses at 1, 3, and 5 hr after administration. The CET concentration in body fluids other than aqueous humor was maintained above the MIC₉₀ values of Streptococcus zooepidemicus and Staphylococcus aureus until 5 hr, but it was not maintained above that of S. aureus in bone. CET (22 mg/kg twice a day) is effective for septic arthritis, pleuritis, and peritonitis caused by gram-positive bacteria but ineffective for osteomyelitis.

Orthopedic Infections-Clinical Applications of Intravenous Regional Limb Perfusion in the Field

For the equine veterinarian, orthopedic emergencies are a common occurrence in clinical practice, with traumatic wounds of the distal limb and penetrating injuries of the hoof being some of the most common medical conditions to affect horses. Intravenous regional limb perfusion is a technique widely used for the treatment of orthopedic infections in horses. The objectives of this review are to discuss some of the clinical applications for this treatment modality in the field and to review the technique for the practitioner.

Meropenem Administered via Intravenous Regional Limb Perfusion for Orthopedic Sepsis in Horses: A Clinical Retrospective Study

Septic synovitis is a critical orthopedic condition in horses. Early intervention is key, with antibiotic therapy typically initiated prior to culture and susceptibility reports becoming available. The pharmacokinetics of several antibiotics have been studied in horses for use in intravenous regional limb perfusion (IVRLP) for septic synovitis, including the carbapenem antibiotic, meropenem. For a variety of factors, some veterinary clinicians may select IVRLP meropenem as therapy for these cases. Meropenem is a vital antibiotic in human medicine, making veterinary use divisive. However, verifying the efficacy of meropenem contrasted to other IVRLP antibiotics is essential for appropriate antimicrobial stewardship. To investigate this, equine patient medical records at a single veterinary teaching hospital were examined. Cases treated with meropenem or gentamicin via IVRLP for septic synovitis were retrospectively analyzed for demographics, diagnostics, treatments, outcomes, and adverse effects. Twenty-three meropenem and 37 gentamicin treated horses were analyzed; demographic information was similar between groups. In the meropenem group, nine horses received meropenem only; the remainder received another antibiotic initially then changed to meropenem. Structures infected included joints (meropenem = 13, gentamicin = 17), tendon sheaths (meropenem = 5, gentamicin = 8) and navicular bursae (meropenem = 2, gentamicin = 6). Overall survival to discharge was 86% (52/60), with meropenem 91% (21/23) and gentamicin 84% (31/37), with no statistically significant differences noted between meropenem or gentamicin groups for overall survival to discharge or outcome after discharge. Twenty-four of 26 bacterial isolates obtained from culture were reported as sensitive to imipenem, a carbapenem antibiotic similar to meropenem. Reported susceptibility to other antibiotics such as ceftiofur (n = 22/26), ampicillin (n = 18/26), amikacin (n = 15/26), or gentamicin (n = 12/26) was also frequently present. In the population of this study, antimicrobial activity augmented with IVRLP using either meropenem or gentamicin both appear to be an effective treatment for septic synovial structures, therefore, less critical antimicrobials may be a viable and more judicious treatment option.

Equine antimicrobial therapy: Current and past issues facing practitioners

Equine antimicrobial therapy has advanced over time with the availability of increasing pharmacokinetic and pharmacodynamic studies in horses, allowing for greater evidence-based clinical decision-making. However, many challenges to optimal antimicrobial therapy remain and further research is needed to address these areas. There are a limited number of approved antimicrobials for use in horses, which creates a need for compounded preparations for clinicians. Extra-label drug use is commonplace in equine practice, which warrants continual education of veterinarians about policies and updates. Performance and competitive horses have their own unique concerns when it comes to antimicrobial use and drug testing. In keeping with the use of a broader range of antimicrobials over time, antimicrobial resistance is emerging as an important issue facing veterinary medicine, including equine practice. Another challenge is that of drug interactions and adverse drug events for which there are little scientific data available for horses, especially for critically important diseases such as Rhodococcus equi infection. Finally, much progress has been made in the availability of equine-specific antimicrobial susceptibility break points. These aid clinicians in interpreting culture and susceptibility results and antimicrobial selection. Even with these advances, continuing education and further research are needed in this area.

Synovial sepsis of unknown origin in the adult Thoroughbred racehorse

BACKGROUND

Synovial sepsis of unknown origin is a rare cause of lameness in the adult horse, and a haematogenous pathogenesis has been proposed in previous cases.

OBJECTIVES

To describe the features and outcome of synovial sepsis of unknown origin in adult Thoroughbred racehorses.

STUDY DESIGN

Retrospective case series.

METHODS

Hospital records for admissions between 2005 and 2015 were reviewed to identify adult horses diagnosed with synovial sepsis of unknown origin. Presentation, clinicopathological, microbiological and diagnostic imaging findings were recorded. Treatment methods, surgical findings, complications and long-term outcome were evaluated.

RESULTS

Eleven cases were identified over the study period. Diagnosis was established from clinical examination and clinicopathologic findings, which were comparable to other aetiologies of synovial sepsis. Affected structures included synovial joints, tendon sheaths and bursae. Concurrent osteochondritis dissecans or articular cartilage lesions were evident during arthroscopic surgery in three cases. Significant intrasynovial haemorrhage was not identified. Microbial culture of synovial fluid or synovial biopsy was positive in 6/11 of cases, with all isolates being Gram-positive cocci. Of the 6 positive microbial cultures, all isolates demonstrated in vitro sensitivity to a cephalosporin antimicrobial agent. A concurrent remote wound was present in a single case. No other potential origins of bacteraemia were identified. Treatment methods included endoscopic surgery, standing multineedle lavage, intravenous regional limb perfusion, intrasynovial medication and/or systemic antimicrobial administration. All horses survived to hospital discharge. For the 6/11 cases that raced following synovial sepsis, the median period for return to racing was 221 days.

MAIN LIMITATIONS

A small study population, which was retrospectively reviewed.

CONCLUSIONS

Synovial sepsis of unknown origin is rare in the adult Thoroughbred racehorse and can affect a range of synovial structures. A concurrent potential source of bacteraemia is rarely identified. With appropriate management, the prognosis to return to racing is fair.

Surgical site infection associated with equine orthopedic internal fixation: 155 cases (2008-2016)

OBJECTIVE

To determine the prevalence of surgical site infection (SSI) after internal fixation and to identify risk factors for SSI and nonsurvival.

STUDY DESIGN

Retrospective study.

ANIMALS

One hundred fifty-five horses with long bone fractures or arthrodesis treated by internal fixation at 1 hospital between 2008-2016.

METHODS

Signalment, diagnosis, surgical repair, surgeon, surgical time, antimicrobial use, SSI onset, bacterial identification, and adjunct treatments were recorded. Perioperative variables were analyzed to identify risk factors associated with outcomes.

RESULTS

Surgical-site infection was reported in 22 of 155 (14.2%) horses, which is lower than what has been previously reported (P = .003). Horses with fetlock arthrodesis or ulnar fracture were more likely to develop SSI. Local prophylactic antimicrobial therapy was associated with an increased risk of SSI. Horses with SSI were 12 times (P < .0001) less likely to survive to discharge than horses without SSI. Horses with a fetlock or carpal arthrodesis or those with radial/humeral/femoral fractures were less likely to survive. No association was identified between open fractures, open reduction and internal fixation, or surgical times and SSI.

CONCLUSION

The prevalence of SSI in this population was lower than what has been previously reported. Horses with fetlock or carpal arthrodesis or radial/humeral/femoral fractures were at increased risk for SSI and/or nonsurvival to discharge. A protective role of local antimicrobial therapy for SSI could not be established.

CLINICAL RELEVANCE

The impact of SSI on outcomes of cases of equine internal fixation remains substantial. Identification of cases at higher risk of SSI should influence surgical technique, postoperative management, and early intervention when SSI is suspected. Additional investigation is warranted regarding local antimicrobial therapy.