Science Digest: How do the development and persistence of antimicrobial resistance in feline microbiota compare after cefovecin or amoxicillin-clavulanic acid treatment?

13 November 2026

Cefovecin (FOV) is the most commonly used or second most commonly used antimicrobial to treat feline urinary tract infections, respiratory infections, and skin infections, despite not being recommended as a first-line treatment for any of these presentations.¹ When not treated with FOV, cats are typically treated with oral amoxicillin-clavulanic acid (AMC), which is a recommended first-line treatment for these infections. Yet despite its frequency of use in both healthy and sick cats, the impact of FOV on feline microbiota is currently unknown.

A study by researchers at the College of Veterinary Medicine at Cornell University and published in the Journal of the American Veterinary Medical Association is the first to characterise and compare the emergence and persistence of antimicrobial resistance in feline gastrointestinal bacteria following two common antimicrobial treatments – FOV or AMC – in clinical settings.

A total of 19 cats were recruited from multiple locations; the Cornell University Small Animal Community Practice (SACP), the Cornell University Hospital for Animals emergency service, the Society for the Prevention of Cruelty to Animals (SPCA) of Tompkins County, and Cornell University community members. Inclusion criteria for cats were a minimum of 5 months old; treated with FOV or AMC; only 1 cat enrolled per household; and the owner(s) or shelter were able to comply with the 12-week follow-up period. The most common primary reasons for antimicrobial treatment were dental procedure prophylaxis, skin infections, wounds, and dental or surgical site infection/dehiscence.

Nine cats were treated with FOV and 10 cats treated with AMC. Antimicrobial treatment selection, dosage and duration was not randomised but was decided at the discretion of the attending vet and influenced by existing prescribing practices at each practice. Vets at the SPCA and SACP were recommended to use 12.5 mg/kg of AMC orally twice a day for 10 days, or a single 8-mg/kg FOV injection. Of the cats in the AMC group, 5 received a 14-day course, 1 received a 10-day course, and 4 received a 7-day course (under the dose recommended by the study protocol). Of the FOV treated cats, 3 were underdosed compared to the recommended protocol.

Faecal samples from the cats were collected on the first day of treatment and at 1, 2, 3, 4, 8, and 12 weeks afterwards. Samples were cultured for Escherichia coli (E. coli), Kirby-Bauer disk diffusion was performed, and isolates with decreased cefovecin susceptibility counted. Direct faecal resistome profiling was performed and the proportions of non-susceptible isolates were compared across treatments and time.

The findings showed that both FOV and AMC selected for ampicillin-resistant E. coli, but ampicillin resistance persisted for longer in FOV-treated cats, and FOV also selected for resistance to higher-tier β-lactams. E. coli susceptibility was generally high (> 85%) across all treatment groups, antimicrobials, and time points.

FOV-treated cats had significantly greater odds of shedding E. coli not susceptible to AMC, ceftriaxone, and cefoxitin, which was largely driven by one FOV-treated cat shedding resistant E. coli for weeks 1 to 4.

Decreased ampicillin susceptibility was observed in isolates from both treatment groups during the first 3 weeks after treatment, however, resistance persisted until week 8 in FOV-treated cats. Isolates from FOV-treated cats, on average, also showed lower susceptibility to multiple antimicrobials, including AMC, cefazolin, ceftriaxone, cefoxitin, FOV, and tetracycline, during weeks 1 to 4. However, the differences in enhanced penicillin and cephalosporin susceptibility were driven primarily by resistant isolates from 1 FOV-treated cat. Reduced susceptibility to β-lactams was observed in AMC-treated cats across all treatment durations (7, 10, and 14 days).

The limitations of the study were the small sample size, stratification of treatment by recruitment site, and the observational design rather than a randomised controlled trial.

Take home message

Cefovecin (FOV) treatment was associated with a greater likelihood and more persistent selection of β-lactam-resistant E. coli in the feline gastrointestinal tract than amoxicillin-clavulanic acid (AMC), although this effect was primarily driven by one FOV-treated cat.

Although only a minority of cats treated with FOV will develop resistance to high-level β-lactams, some treated cats shedding β-lactam–resistant E. coli may pose a threat to feline and human health. The risk of antimicrobial resistance is likely lower after AMC treatment.

Reference

¹Cazer CL, Siler J, Frye A, Reboul GC, Yu YT, Sams K et al. (2026) Cefovecin selects for higher-level and more persistent antimicrobial resistance among gastrointestinal Escherichia coli in some cats compared to amoxicillin–clavulanic acid in an observational longitudinal study. Journal of the American Veterinary Medical Association. doi.org/10.2460/javma.26.03.0235

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