Which high‑quality non‑randomised studies evaluating oral antibiotic prophylaxis (without mechanical bowel preparation) in adults undergoing elective colorectal resection should be included in a meta‑analysis?

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Last updated: October 9, 2026 • View editorial policy

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Studies for Meta-Analysis on Oral Antibiotic Prophylaxis Without Mechanical Bowel Preparation

Based on the evidence provided, you should NOT conduct this meta-analysis as currently framed, because high-quality non-randomized studies specifically evaluating oral antibiotics WITHOUT mechanical bowel preparation are essentially non-existent in the literature.

Critical Evidence Gap

The 2019 ERAS guidelines 1 explicitly state: "oral antibiotic decontamination alone in patients with no bowel preparation has not been studied and any potential effect remains unknown." This is a fundamental limitation that makes your proposed meta-analysis impossible with current evidence.

What the Evidence Actually Shows

Available Study Types:

The largest observational study from the ACS NSQIP database 1 included 40,446 patients with the following groups:

  • No preparation: 13,219 patients (32.7%)
  • Mechanical bowel preparation alone: 13,935 patients (34.5%)
  • Oral antibiotic preparation alone: 1,572 patients (3.9%) ← This is your target group
  • Combined MBP + oral antibiotics: 11,720 patients (29.0%)

Key finding: Oral antibiotic preparation alone was protective against surgical site infection (OR 0.63,95% CI 0.45-0.87), anastomotic leak (OR 0.60,95% CI 0.34-0.97), ileus (OR 0.79,95% CI 0.59-0.98), and major morbidity (OR 0.73,95% CI 0.55-0.96) 1.

The Problem:

"However, to date no RCTs have been performed to support this observation, and as such, further high-quality evidence is necessary to inform the debate" 1.

The ERAS guidelines rate the evidence quality for oral antibiotics alone as "Low" with a "Weak" recommendation grade 1.

Studies You Could Actually Include

Non-Randomized Studies:

  1. The ACS NSQIP database study (referenced as 118 in the guidelines) - 40,446 patients, with 1,572 receiving oral antibiotics alone 1

  2. The 2022 NSQIP analysis 2 - 30,939 patients over 7 years (2012-2018), showing oral antibiotic utilization increased from 2.3% to 5.5%, but this study primarily compared oral antibiotics alone versus combined MBP + oral antibiotics

What These Studies Actually Compared:

The 2022 study 2 found that for colon cancer patients, those with oral antibiotics alone had higher superficial SSI rates than combined MBP + oral antibiotics (1.9% vs 1.1%; p=0.043). For rectal cancer, oral antibiotics alone showed higher deep SSI rates (0.9% vs 0.1%; p=0.004).

Why This Meta-Analysis Cannot Proceed as Designed

The fundamental issue: Nearly all existing studies evaluate oral antibiotics in combination with mechanical bowel preparation, not oral antibiotics alone without MBP. The 2015 study 3 showing 50% SSI reduction used oral antibiotics, but the comparison groups were "no preparation" and "MBP only" - not a clean evaluation of oral antibiotics without MBP.

The 2026 meta-analysis 4 included 12 trials with 4,073 patients, but all compared MBP + oral antibiotics versus MBP alone - not oral antibiotics without MBP.

What You Should Do Instead

Reframe your research question to one of these answerable questions:

  1. Oral antibiotics + MBP versus MBP alone (abundant RCT evidence available)
  2. Oral antibiotics alone versus no preparation (limited observational data only)
  3. Oral antibiotics alone versus systemic antibiotics alone (very limited data)

Common Pitfall to Avoid:

Do not conflate studies examining "oral antibiotics without additional MBP" with studies examining "oral antibiotics in the absence of MBP." Most studies use oral antibiotics with MBP as standard practice.

The ERAS guidelines explicitly state: "No recommendation for the use of oral antibiotic decontamination can be given for patients having no bowel preparation" 1.

References

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