Background: Surgical site infection (SSI) is the most common problem after surgery. Although several guidelines have indicated the efficacy of antiseptics, such as chlorhexidine-alcohol and povidone-iodine, in reducing SSI rate, the optimal recommendation is still not established. Olanexidine might have higher bactericidal activity than other antiseptic agents. However, no randomised study has evaluated the efficacy and safety of olanexidine over conventional antiseptics. We compared the effect of aqueous olanexidine and aqueous povidone-iodine on the incidence of SSI following clean-contaminated surgery. Methods: This was a multicentre, prospective, randomised, blinded-endpoint superiority trial for surgical skin antisepsis in clean-contaminated gastrointestinal and hepatobiliary pancreatic surgeries in four Japanese hospitals. Patients aged 20 years or older who underwent elective clean-contaminated wound surgery were randomly assigned in a 1:1 replacement ratio using a computer-generated block randomisation. Patients were randomly assigned to surgical skin antisepsis with an aqueous formulation of 1·5% olanexidine or surgical skin antisepsis with an aqueous formulation of 10% povidone-iodine before surgery. We used olanexidine in a ready-to-use applicator, and povidone-iodine was administered by a brush or by compression using pliers. Both antiseptics were applied from the papilla with a cranial limit and to the upper thigh with a caudal limit. The antiseptics were allowed to dry for 3 min, and then surgery started. Participants, some investigators, and data analysts were masked to treatment allocation. Participant enrolment was done by non-masked investigators. The primary outcome was 30-day SSI assessed in the intention-to-treat population. The surgical wound site of each participant was observed daily. After discharge, participants underwent at least one outpatient visit within 30 days after surgery. This trial is registered with University hospital Medical Information Network, 000031560. Findings: Between June 10, 2018, and April 18, 2019, 883 patients were assessed for eligibility. 587 patients were eligible and 294 received olanexidine and 293 received aqueous povidone-iodine before surgery. 30-day SSI occurred in 19 (7%) patients in the olanexidine group and 39 patients (13%) patients in the povidone-iodine group (adjusted risk difference −0·069; 90% CI −0·109 to −0·029; adjusted risk ratio [RR] 0·48, 90% CI 0·30 to 0·74; p=0·002). Five patients (2%) in the olanexidine group and five (2%) in the povidone-iodine group developed adverse skin reactions (adjusted RR 0·99, 95% CI 0·29 to 3·40; p=1·00). Interpretation: Olanexidine significantly reduced the occurrence of overall SSI and superficial incisional SSI compared with aqueous povidone-iodine in clean-contaminated surgery. Our results indicate that olanexidine might have a role to prevent SSI in patients who undergo clean-contaminated surgeries. Funding: Keio University and Ohyama Health Foundation.
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