The increase in antimicrobial resistance (AMR) is a global health threat, impacting both human and animal populations. The World Health Organisation (WHO) estimated that in 2019, AMR was directly associated with 1.27 million deaths worldwide (WHO, 2024). Horses play a crucial role in “One Health” policies through their involvement both with human handlers and the environment (Kabir et al., 2024). Furthermore, almost half of zoonotic pathogens transmitted by horses are bacterial (Sack et al., 2020). The injudicious use of antimicrobials positively selects for resistant genes (Steinman and Navon-Venezia, 2020).

Horses and humans have interacted closely for hundreds of years, with horses playing an integral role in the development of modern societies. In the present day, human-horse interactions are possibly closer than before in history, with horses used not only for sport and as working animals, but also for companionship (Merkies and Franzin, 2021). In addition to the potential for direct transmission of multi-drug resistant bacteria (MDR) between horses and humans, the transfer of antibiotic-resistant genes between bacteria within the environment also drives the development of AMR. As such, managing antibiotic use in veterinary species is crucial as part of a “One Health” approach to tackling AMR.

Antimicrobials are invaluable in treating bacterial infections in horses and as such their use cannot be stopped entirely, for fear of adversely compromising animal welfare. With the rise in AMR, the reduced efficacy of these valuable drugs and negative clinical outcomes are increasingly evident, in addition to the economic impact of this through prolonged hospitalisation and increased treatment costs (Kabir et al., 2024). A further reason in support of the prudent use of antimicrobials in horses is their susceptibility as a species to the adverse effects of these drugs, which range from appetite changes and allergic reactions to potentially fatal antibiotic-associated diarrhoea (AAD) (Khusro et al., 2021). Whilst the development of transient bacteraemia has been identified in horses undergoing exodontia (Kern et al., 2017) and this has been linked to the development of sepsis or remote infections in humans, no such link has yet been established in horses (Parahitiyawa et al., 2009; Wilson et al., 2007; Wagner et al., 2006.) There are numerous case reports detailing the complications associated with equine dental and sinus procedures, including cellulitis, localised abscessation, and meningitis (Zetterström et al., 2021; Bach et al., 2014; Horbal et al., 2019; Racine et al., 2017). However, the prophylactic use of antibiotics does not necessarily prohibit infection-associated complications after dental or sinus procedures (Vlaminck et al., 2001; Zetterström et al., 2021). Furthermore, bacteraemia in horses undergoing exodontia was not associated with adverse clinical outcomes in the absence of antibiotic administration (Kern et al., 2017), and complication rates are comparable between horses who underwent dental extractions with (18.4%) and without (16.3%) perioperative antibiotics. (Christiansen et al., 2023).

In man, transient bacteraemia occurs variably during dental extractions, but also during everyday activities such as tooth brushing (Forner et al., 2006)(Lockhart et al., 2008). These bacteria are either immediately oxidised within the bloodstream by circulating erythrocytes or later destroyed by the reticuloendothelial system (RES) (Minasyan, 2016). Dental disease accounts for around 10% of antibiotic use in human patients in Western nations, although it is suggested that 81% of these prescriptions are unnecessary (Thompson, 2022; Smith et al., 2020).

Reported antibiotic use during dental procedures in companion animals ranges from 4.4-8.8%, with comorbidities increasing the likelihood of antibiotics being prescribed to combat suspected bacteraemia (Ljungquist et al., 2024; Soltero-Rivera et al., 2024). In contrast, antibiotics are frequently prescribed as a first-line treatment for certain dental conditions and secondary dental sinusitis, or in conjunction with other modalities in the treatment dental and sinus disease (Godoy et al., 2023). Current human guidelines in the UK do not recommend the use of antibiotics to prevent post-operative complications in most dental procedures, even in medically-compromised individuals, save in instances of oro-antral communication resulting in sinusitis (Palmer, 2020). There is little consensus on the use of perioperative antibiotics in cases of dental extractions in horses (Dixon, 2023), but the use of both systemic and local antibiotics in the management of various dental disorders, including dental fractures, pulpar exposure, oral soft tissue trauma, periapical infection, and in the perio-operative period, is frequently described in the literature and in textbooks. If it is decided that perioperative antibiotics are to be administered, clinicians then must decide upon the drug timing of administration, and duration of treatment. The goal of perioperative antimicrobial is to decrease the likelihood of infection after exposure to bacteria during the surgical period, with guidelines typically recommending antimicrobial administration for the shortest effective period possible (Steinman et al., 2015).

Additionally, antimicrobials should be selected based on the susceptibility of those pathogens likely to be involved in clinical disease. Recent studies have provided valuable insight into the equine oral microbiome (Kennedy et al., 2016), which may help clinicians select antimicrobials more appropriately. Ideally, these would be ‘first-line’ antibiotics based on peer-reviewed guidance, with highest priority critically important antimicrobials (HPCIAs) only chosen based on culture and sensitivity results.

The existing evidence suggests that practitioners are choosing wisely where there is clinical disease. Doxycycline, oxytetracyline, and trimethoprim-sulfadiazine are reported as amongst the most frequently prescribed ‘first-line’ treatment choices in cases of dental sinusitis (Souza et al., 2024) and dental disorders were not specifically listed as typical clinical scenario in which HCPAIs would be used (Wilson et al., 2023).

Further antimicrobial surveillance is required in the field of equine dentistry, both at a clinical level, to establish common prescribing patterns and report antimicrobial consumption, and at a micro- biological level to investigate evolving patterns of resistance in equine oral pathogens. Additionally, further work must be done to better understand the clinical outcomes of horses treated for dental disease with and without antimicrobials. 

References
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