Equine antimicrobial therapy: Current and past issues facing practitioners

Abstract

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.

Changes in the Fecal Microbiota Associated with a Broad-Spectrum Antimicrobial Administration in Hospitalized Neonatal Foals with Probiotics Supplementation

“…Only one broadspectrum IV antimicrobial combination was investigated in the present study, thus the effect on fecal bacterial microbiota of different routes or combinations is unknown. Interestingly, the most profound impact on fecal microbiota has been reported from days 2 to 5 in adult horses when different antimicrobials are administered [20,27,28]. Albeit we did not perform a sequential sampling, this is comparable with the earliest time at which an effect was detected in our study (two foals that received 5 days of treatment).…”

“…Interestingly, the most profound impact on fecal microbiota has been reported from days 2 to 5 in adult horses when different antimicrobials are administered [ 20 , 27 , 28 ]. Albeit we did not perform a sequential sampling, this is comparable with the earliest time at which an effect was detected in our study (two foals that received 5 days of treatment).…”

“…The effects of probiotics on the microbiota changes could not be determined nor discriminated in the present population, and further studies are needed to compare foals administered broad-spectrum antimicrobials with or without probiotics supplementation. Overall, the evidence for probiotics use in horses and foals is not consistent [ 18 , 19 , 28 , 66 ]. It was previously hypothesized that probiotics might be of more benefit in foals than adults [ 67 ], however, Schoster et al (2016) [ 68 ] did not detect an increase in Lactobacillus and Bifidobacterium in neonatal foals receiving a multistrain probiotics product.…”

“…A few reports exist exploring the effects on gut microbiota of a broad-spectrum antimicrobial therapy in adult horses [ 20 , 26 , 27 , 28 ]. Antimicrobial resistance is also an alarming and emerging challenge in equine medicine [ 17 ].…”

Analysis of Virulence and Antimicrobial Resistance Gene Carriage in Staphylococcus aureus Infections in Equids Using Whole-Genome Sequencing

“…Antimicrobial resistance, often to multiple classes of drugs, is a significant problem in S. aureus , and resistance genes are frequently carried on mobile genetic elements (MGEs) and can be passed among isolates. Trimethoprim-sulfamethoxazole (TMS) drugs and aminoglycosides are commonly used to treat infections in horses as they provide broad spectrum antimicrobial coverage ( 22 , 23 ). The genes conferring high-level aminoglycoside resistance in S. aureus are aac (6′)-Ie/aph (2′') and aph (3′)-IIIa , and kanamycin-neomycin resistance genes ant (4′)-Ia or aadD are carried on plasmids ( 24 ).…”