Oral neomycin and bacitracin are effective in preventing surgical site infections in elective colorectal surgery: a multicentre, randomized, parallel, single-blinded trial (COLORAL-1).

Several regimens of oral and intravenous antibiotics (OIVA) have been proposed with contradicting results, and the role of mechanical bowel preparation (MBP) is still controversial. This study aims to assess the effectiveness of oral antibiotic prophylaxis in preventing Surgical Site Infections (SSI) in elective colorectal surgery. In a multicentre trial, we randomized patients undergoing elective colorectal resection surgery, comparing the effectiveness of OIVA versus intravenous antibiotics (IVA) regimens to prevent SSI as the primary outcome (NCT04438655). In addition to intravenous Amoxicillin/Clavulanic, patients in the OIVA group received Oral Neomycin and Bacitracin 24 h before surgery. MBP was administered according to local habits which were not changed for the study. The trial was terminated during the COVID-19 pandemic, as many centers failed to participate as well as the pandemic changed the rules for engaging patients. Two-hundred and four patients were enrolled (100 in the OIVA and 104 in the IVA group); 3 SSIs (3.4%) were registered in the OIVA and 14 (14.4%) in the IVA group (p = 0.010). No difference was observed in terms of anastomotic leak. Multivariable analysis indicated that OIVA reduced the rate of SSI (OR 0.21 / 95% CI 0.06–0.78 / p = 0.019), while BMI is a risk factor of SSI (OR 1.15 / 95% CI 1.01–1.30 p = 0.039). Subgroup analysis indicated that 0/22 patients who underwent OIVA/MBP + vs 13/77 IVA/MBP- experienced an SSI (p = 0.037). The early termination of the study prevents any conclusion regarding the interpretation of the data. Nonetheless, Oral Neomycin/Bacitracin and intravenous beta-lactam/beta-lactamases inhibitors seem to reduce SSI after colorectal resections, although not affecting the anastomotic leak in this trial. The role of MBP requires more investigation.