Effect of surgical antimicrobial prophylaxis duration for colic surgery on complications and resistome.
Authors: Southwood Louise L, Long Alicia, Perez Jairo, Daniel Scott, Bittinger Kyle, Aitken Maia, Redding Laurel
Journal: Equine veterinary journal
Summary
# Editorial Summary: Surgical Antimicrobial Prophylaxis Duration in Equine Colic Surgery Prolonging surgical antimicrobial prophylaxis (SAP) beyond 24 hours following colic surgery offers no clinical benefit and may unnecessarily promote antimicrobial resistance, according to this prospective randomised trial comparing outcomes in 140 horses treated with either 24 or 72 hours of penicillin and gentamicin. Researchers assessed both conventional clinical complications—including incisional infection, which occurred in approximately 17% of the 24-hour group and 16% of the 72-hour group—and microbial changes via faecal metagenomic sequencing in a subset of 49 horses, using the AMR++ pipeline to quantify resistance gene profiles. Whilst antibiotic administration initially reduced microbiome diversity and predictably elevated resistance genes to the administered drugs, the 72-hour protocol resulted in significantly higher discharge levels of beta-lactam resistance genes without reducing post-operative complications, suggesting that extended prophylaxis drives resistance without clinical advantage. These findings align with evidence from human surgery and support the recommendation for 24-hour SAP as standard practice in equine colic cases, potentially reducing selective pressure on commensal flora and limiting resistance emergence in individual patients and populations. The study's primary limitations—single-hospital setting and clinician awareness of treatment assignment—warrant cautious interpretation, though the consistency of the microbiological findings strengthens confidence in the core message for practitioners implementing prophylaxis protocols.
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Practical Takeaways
- •Limit surgical antimicrobial prophylaxis to 24 hours for colic surgery in horses—extending to 72 hours provides no clinical benefit and increases antimicrobial resistance
- •Shorter prophylaxis duration helps preserve the normal faecal microbiome and reduces selection pressure for resistant bacteria in surgical patients
- •Incisional infection rates are comparable whether using 24- or 72-hour prophylaxis protocols, supporting evidence-based stewardship practices
Key Findings
- •No significant difference in incisional infection rates between 24-hour (17%) and 72-hour (16%) surgical antimicrobial prophylaxis groups (p=0.9)
- •Time was the primary driver of microbiome/resistome changes, with alpha diversity decreasing and antimicrobial resistance genes increasing between admission and discharge
- •Discharge beta-lactam resistance genes were significantly higher in the 72-hour group compared to the 24-hour group
- •24-hour surgical antimicrobial prophylaxis is as effective as 72-hour prophylaxis for preventing complications in horses undergoing colic surgery