Infectious Diseases

Preventing post-op infections: Stick to the short course

By Adam Marcus

When it comes to preventing postoperative infections, a recent study shows less is more. Veterinarians can limit the course of prophylactic antibiotics to 24 hours in horses undergoing colic surgery without increasing the risk for infectious complications.

“There is no evidence in human or veterinary surgery that surgical antimicrobial prophylaxis should extend beyond 24 hours, and ideally it should be even shorter than 24 hours,” said Louise L. Southwood, PhD, DACVS, DACVECC, a professor of large animal emergency medicine and critical care at the University of Pennsylvania School of Veterinary Medicine’s New Bolton Center, who led the research. “Any antimicrobial administration beyond 24 hours should be considered therapeutic and reserved for pre-existing infections.”

For the randomized trial, Dr. Southwood and her colleagues compared outcomes among 140 adult horses that underwent colic surgery. Of those, 71 received the 24-hour course of antibiotic prophylaxis, and 69 received the drugs for 72 hours.

The researchers observed no statistically significant differences in complications linked to the 2 drug regimens. In the 24-hour group, 16 animals developed incisional infections, compared with 17 in the 72-hour arm (P=0.9). Although the horses that received the shorter course tended to be younger than those in the other group, age had no effect on the incidence of infection, they found.

To assess the effects of the 2 approaches on the gut microbiomes, Dr. Southwood and her colleagues analyzed fecal samples from 49 of the horses. And here, key differences emerged. The longer course of antibiotics was associated with more changes to the animals’ gut microbiome, including in genes associated with antibiotic resistance—particularly those involving the response to beta-lactam agents such as penicillin, carbapenems and cephalosporine compounds.

Relevance
“The observation of beta-lactamase genes is concerning; however, penicillin is such a good antimicrobial in horses, and of a lower priority for humans, it is still a good first-line equine antimicrobial,” Dr. Southwood said. “If we could use something like IV trimethoprim-sulfamethoxazole [TMP-SMX], it might be even better, but their IV use is complicated in adult horses.”

Given the potential issue with beta-lactams, should veterinarians avoid using the drugs in horses that require post-op antimicrobials? Not necessarily, Dr. Southwood said.

“Antimicrobial therapy for septic peritonitis, for example, should be based on cytology to identify the type of bacteria, culture and sensitivity testing of the fluid, and confirming that it is not based on intestinal necrosis or leakage, which would require repeat laparotomy or euthanasia,” she said.

Initial empirical treatment of septic peritonitis should involve the use of broad-spectrum agents, and either oral antimicrobials or IV penicillin and gentamicin, she added.

Pneumonia and colic
Pneumonia after colic surgery, as another example, is often associated with aspiration that occurred at some point during the disease or treatment. For cases where clinical signs are mild or moderate but persistent, a broad-spectrum oral antimicrobial such as TMP-SMX or minocycline is appropriate, she said, as is a probiotic to prevent the onset of colitis when oral drugs are prescribed.

When the pneumonia is more severe, Dr. Southwood said she often restarts penicillin and gentamicin. “I always try to avoid third- and fourth-generation cephalosporins and fluoroquinolones, at least empirically, because of their high priority [for human use] status as ranked by the World Health Organization,” she added.

Could giving equine patients probiotics during the perioperative period help mitigate changes in their gut flora? Dr. Southwood said the data here are unclear.

“The benefit of probiotics is definitely up for debate, especially regarding any benefit to the postoperative colic patient,” she said. Although she does provide Saccharomyces boulardii and mannan oligosaccharide as a prebiotic when administering oral antimicrobials, “I have no proof of its efficacy; it just makes me feel like I am doing something to prevent antimicrobial-associated colitis.” MeV

Related listening: in Colic in Horses, an Equine Express Podcast episode, Dr. Louise Southwood discusses colic surgery decisions, postoperative care and recovery.

FOR MORE INFORMATION
Southwood LL, Long A, Perez J, et al. Effect of surgical antimicrobial prophylaxis duration for colic surgery complications and resistome. Equine Vet J. 2025 Dec. 10. https://doi.org/10.1002/evj.70137
https://beva.onlinelibrary.wiley.com/doi/10.1002/evj.70137