Background: Perioperative antibiotic prophylaxis is crucial in improving outcomes after colorectal surgery. While guidelines in elective procedures are well established, evidence in emergency settings remains limited. This study evaluated the association between antibiotic timing before incision and 30-day mortality as well as surgical site infections (SSIs) in emergency colorectal surgery.

Study design: This nationwide retrospective cohort study analysed colorectal surgery cases from the Swiss national infection surveillance programme. Demographics, antibiotic regimens, and surgical characteristics of consecutive cases were compared between elective and emergency procedures. Independent predictors of 30-day mortality and SSIs were identified using multivariable logistic regression adjusted for patient and surgical factors. Timing of antibiotic administration was modelled using natural cubic splines to assess non-linear effects.

Results: Among 63,945 patients, 16,939 (26.5%) underwent emergency procedures. In the fully adjusted model, antibiotic timing was significantly associated with 30-day mortality ( p < 0.001) in both elective and emergency surgeries. A U-shaped pattern was observed, with lowest predicted 30-day mortality when antibiotics were administered 48 minutes before incision in elective (mean 1.28%, 95% CI 1.15-1.40) and 51 minutes before incision in emergency surgeries (mean 10.50%, 95% CI 9.71-11.20). In contrast, antibiotic timing was not significantly associated with SSIs ( p = 0.229).

Conclusion: In both elective and emergency colorectal surgery, early or late antibiotic administration relative to incision was associated with increased 30-day mortality. The lowest risk occurred when antibiotics were administered approximately 50 minutes before incision. These findings support optimising perioperative antibiotic timing to improve postoperative outcomes in emergency colorectal surgery.