The purpose of the study is to determine if short-term outcomes of rectal resections after full bowel preparation (mechanical bowel preparation plus oral antibiotics) are superior to rectal resections with only mechanical bowel preparation.

The design involves random allocation of eligible patients to full bowel preparation or only mechanical bowel preparation in 1:1 ratio. After that rectal resection is performed in both groups.

Short-term outcomes are assessed in 30 day period after surgery. This is a superiority trial evaluating statistical superiority. Rate of surgical site infection is anticipated to decrease from 12% (data from local registry) to 6%. For power of 80% enrolment of 622 patients is required.

The intent-to-treat principle is used for the data analysis.

Inclusion Criteria:

• histologically confirmed adenocarcinoma of the rectum or rectosigmoid junction
• clinical stage T1-4aN0-2M0-1 (distant metastases must be resectable)
• indications for surgical rectal resection
• ECOG status 0-2
• At least 18 years of age
• Written informed consent

Exclusion Criteria:

• Medical or psychiatric conditions that compromise the patient's ability to give informed consent or comply with the study protocol
• Pregnancy or breast feeding
• Medical contraindications for surgical treatment
• Any use of antibiotics 30 days prior to inclusion
• Functioning stoma
• Contraindications for use of MBP or OA drugs or their components
• Indications for obstructive resection or abdominoperineal excision
• Acute bowel obstruction, bleeding or perforation
• Other malignancies not in remission

We are not planning to share individual participant data