In adults (≥18 years) undergoing elective colon or rectal resection, does adding pre‑operative oral antibiotics to mechanical bowel preparation reduce postoperative surgical site infection and related complications compared with mechanical bowel preparation alone?

Meta-Analysis Proposal: Oral Antibiotics Plus Mechanical Bowel Preparation vs. MBP Alone in Elective Colorectal Surgery

Research Question

In adults (≥18 years) undergoing elective colon or rectal resection with mechanical bowel preparation, does the addition of preoperative oral antibiotics reduce surgical site infections, anastomotic leak, and mortality compared with mechanical bowel preparation alone?

Rationale

The 2019 ERAS guidelines 1 acknowledge that while MBP alone shows no benefit, emerging evidence suggests combining oral antibiotics with MBP significantly reduces SSI (RR 0.48,95% CI 0.44-0.52). However, the guidelines rate this evidence as low quality with weak recommendation grade, explicitly stating "further high-quality evidence is necessary to inform the debate" and noting "to date no RCTs have been performed to support this observation" 1. This creates a critical evidence gap that your meta-analysis can address.

Recent studies 2, 3, 4 published in 2025-2026 have now provided the RCT evidence that was missing when the 2019 guidelines were written, making this an ideal time for an updated systematic review.

PICO Framework

Population

• Adults ≥18 years undergoing elective colorectal resection (colon or rectal)
• Both cancer and benign disease
• Separate subgroup analyses for:
  • Colon vs. rectal resections
  • Cancer vs. benign pathology
  • Laparoscopic vs. open approach

Intervention

• Mechanical bowel preparation (MBP) + oral antibiotics (OAB) + systemic IV antibiotics

Comparator

• Mechanical bowel preparation (MBP) alone + systemic IV antibiotics

Outcomes

Primary:

• Overall surgical site infection (CDC definition)

Secondary:

• Superficial incisional SSI
• Deep incisional SSI
• Organ/space SSI (including anastomotic leak)
• Anastomotic leak (separately analyzed)
• Mortality (30-day)
• Ileus
• Hospital length of stay
• Reoperation rates
• Clostridium difficile infection

Inclusion Criteria

Study Design

• Randomized controlled trials only
• Published in English
• January 2000 to present (to capture contemporary surgical practice)

Patient Characteristics

• Adults ≥18 years
• Elective colorectal resection with anastomosis
• Both colon and rectal procedures

Intervention Requirements

• Intervention arm: MBP + oral antibiotics + systemic IV prophylaxis
• Control arm: MBP alone + systemic IV prophylaxis
• Oral antibiotic regimens may include:
  • Neomycin + metronidazole
  • Neomycin + erythromycin
  • Kanamycin + metronidazole
  • Rifaximin

Outcome Reporting

• Must report at least one primary or secondary outcome
• SSI defined by CDC criteria preferred

Exclusion Criteria

• Emergency surgery
• No anastomosis performed (e.g., Hartmann's procedure, end colostomy)
• Studies comparing no preparation vs. MBP (different question)
• Studies comparing oral antibiotics alone vs. other regimens
• Pediatric populations
• Non-English publications
• Conference abstracts without full-text availability
• Duplicate patient populations

Search Strategy

Databases

• PubMed/MEDLINE
• Embase
• Cochrane Central Register of Controlled Trials (CENTRAL)
• Web of Science
• ClinicalTrials.gov (for unpublished/ongoing trials)

Search Terms

Combine using Boolean operators:

Population terms:

• "colorectal surgery" OR "colectomy" OR "rectal resection" OR "colon resection" OR "colorectal resection"

Intervention terms:

• "oral antibiotics" OR "oral antibiotic prophylaxis" OR "antibiotic bowel preparation" OR "neomycin" OR "metronidazole" OR "erythromycin"

Comparator terms:

• "mechanical bowel preparation" OR "MBP" OR "bowel preparation"

Outcome terms:

• "surgical site infection" OR "SSI" OR "wound infection" OR "anastomotic leak" OR "anastomotic dehiscence"

Study design filter:

• "randomized controlled trial" OR "RCT" OR "randomised"

Studies to Include Based on Provided Evidence

Based on your evidence review, these studies should definitely be included:

1. 2 Medicina 2026 - Meta-analysis of 12 RCTs, 4,073 patients

   • Reports overall SSI, incisional SSI, organ-space SSI
   • Moderate-to-high certainty evidence

2. 3 Updates in Surgery 2026 - Meta-analysis of 8 studies, 7,516 rectal tumor patients

   • Specific to rectal resections
   • Reports SSI and anastomotic leak

3. 4 Colorectal Disease 2025 - Meta-analysis of 9 RCTs, 3,046 CRC patients

   • Cancer-specific population
   • Includes rectal cancer subgroup (n=1,172)
   • Reports CDC-defined SSI subtypes and AL

4. 5 Int J Colorectal Dis 2023 - Network meta-analysis of 46 RCTs, 12,690 patients

   • Compares different OAB regimens
   • Bayesian analysis approach

5. 6 Colorectal Disease 2020 - Retrospective cohort of 732 patients

   • Note: This is observational, not RCT - may include for sensitivity analysis only

6. 7 Indian J Surg Oncol 2025 - Quasi-experimental study, 99 patients

   • Note: Not truly randomized - may exclude or sensitivity analysis

Additional Studies to Search For

You should search for and extract the primary RCTs cited within these meta-analyses, particularly:

• The 23 RCTs mentioned in the ERAS guidelines meta-analysis 1
• Individual trials from the ACS NSQIP database studies
• Recent RCTs published 2020-2025 not captured in earlier meta-analyses

Data Extraction

Study Characteristics

• First author, year, country
• Study design and registration
• Sample size (per arm)
• Patient demographics (age, sex, BMI, ASA score)
• Surgical indication (cancer vs. benign)
• Surgical approach (open, laparoscopic, robotic)
• Anatomic location (right colon, left colon, rectum)

Intervention Details

• MBP regimen (polyethylene glycol, sodium phosphate, etc.)
• Oral antibiotic regimen (drugs, doses, timing)
• Systemic IV antibiotic regimen
• Timing of all interventions

Outcomes

• Number of events per arm for dichotomous outcomes
• Mean ± SD for continuous outcomes
• Follow-up duration
• Definition of SSI used
• Definition of anastomotic leak

Risk of Bias

• Use Cochrane RoB 2.0 tool
• Assess: randomization, allocation concealment, blinding, incomplete data, selective reporting

Statistical Analysis Plan

Effect Measures

• Dichotomous outcomes: Risk ratio (RR) or odds ratio (OR) with 95% CI
• Continuous outcomes: Mean difference with 95% CI

Meta-Analysis Method

• DerSimonian-Laird random-effects model (anticipate heterogeneity)
• Calculate I² statistic for heterogeneity
• Report 95% prediction intervals for primary outcome

Subgroup Analyses (Pre-specified)

1. Anatomic location: Colon vs. rectum

2. Surgical approach: Open vs. minimally invasive

3. Cancer vs. benign disease

4. OAB regimen type:

   • Neomycin + metronidazole
   • Neomycin + erythromycin
   • Kanamycin + metronidazole
   • Other regimens

5. Geographic region: North America vs. Europe vs. Asia

6. Study quality: Low vs. high risk of bias

Sensitivity Analyses

1. Exclude high risk-of-bias studies
2. Exclude studies with <50 patients per arm
3. Fixed-effect model
4. Exclude observational studies (if included)
5. Trial sequential analysis for primary outcome

Publication Bias Assessment

• Funnel plot (if ≥10 studies)
• Egger's regression test
• Trim-and-fill method
• Contour-enhanced funnel plot

GRADE Assessment

Rate certainty of evidence for each outcome:

• Risk of bias
• Inconsistency
• Indirectness
• Imprecision
• Publication bias

Expected Findings Based on Current Evidence

Based on the provided studies, you should expect:

• Overall SSI reduction: RR ~0.50-0.55 (approximately 45-50% reduction) 2, 4
• Anastomotic leak reduction: OR ~0.40-0.45 3, 4
• Moderate heterogeneity (I² 40-60%) for SSI outcomes 2
• Stronger effect in colon than rectal resections 6
• Kanamycin + metronidazole may be most effective regimen 5

Timeline

• Month 1-2: Literature search and screening
• Month 3: Data extraction and quality assessment
• Month 4: Statistical analysis
• Month 5: Manuscript preparation
• Month 6: Submission and revision

Registration

Register protocol prospectively on PROSPERO before beginning data extraction to enhance transparency and reduce reporting bias.

Key Advantages of This Meta-Analysis

1. Addresses critical evidence gap identified by ERAS guidelines 1
2. Includes recent high-quality RCTs (2020-2026) not in 2019 guidelines
3. Cancer-specific subgroup analysis addresses oncologic population 4
4. Rectal-specific analysis addresses high-risk population 3
5. Regimen comparison identifies optimal antibiotic choice 5
6. Patient-important outcomes including mortality and anastomotic leak

Potential Challenges

• Heterogeneity in OAB regimens - address through subgroup analysis
• Variation in MBP protocols - extract and report systematically
• Different SSI definitions - prioritize CDC-defined outcomes
• Publication bias - search trial registries for unpublished studies
• Overlap between meta-analyses - carefully identify primary studies to avoid double-counting