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This study investigates whether adding metronidazole to meropenem improves clinical efficacy in treating complicated intra-abdominal infections.

June 10, 2026BMC Infectious Diseases0 citationsOpen Access

Effect of adding metronidazole to meropenem on clinical efficacy in complicated intra-abdominal infections: a retrospective study

HNHajime Nakashima MMMotoyasu Miyazaki NNN Nishimura

Key Points

This study investigates whether adding metronidazole to meropenem improves clinical efficacy in treating complicated intra-abdominal infections.
Retrospective study over 9 years including 114 patients with cIAI from lower gastrointestinal perforation.
Analyzed outcomes of empiric therapy with meropenem monotherapy versus meropenem plus metronidazole using propensity score matching.
Primary outcome measured was the cure rate, with secondary outcomes including 28-day mortality and hospitalization duration.
No significant difference in cure rates between groups: 91.2% (MEPM) vs. 91.3% (MEPM+MNZ), p=0.999.
28-day mortality was 2.2% (MEPM) vs. 4.3% (MEPM+MNZ), p=0.495; no significant difference in hospitalization durations, p=0.214.
After propensity score matching, cure rates were 85.0% (17/20) for MEPM and 95.0% (19/20) for MEPM+MNZ, p=0.605, suggesting no clear benefit of adding MNZ.

Abstract

Complicated intra-abdominal infections (cIAI), often caused by a diverse range of organisms, are commonly managed with appropriate empiric antimicrobial therapy, particularly broad-spectrum agents such as meropenem (MEPM). Anaerobes contribute to 30%–80% of the causative pathogens, and Bacteroides fragilis , a typical anaerobe, has been reported to exhibit increased resistance to antimicrobial agents. Metronidazole (MNZ) has shown significant antibacterial activity against anaerobes and a different mechanism of action; therefore, its addition to MEPM may improve its clinical efficacy. This study aimed to evaluate the impact of adding MNZ to MEPM on the clinical efficacy of empiric antimicrobial therapy for cIAI. This retrospective study spanned 9 years and included 114 patients who underwent empiric antimicrobial therapy with MEPM monotherapy or MEPM plus MNZ combination therapy for cIAI caused by lower gastrointestinal perforation in conjunction with surgery or percutaneous drainage. Propensity score matching was applied to adjust for background factors. The primary outcome was the cure rate, while secondary outcomes included 28-day mortality and the duration of hospitalization following surgical intervention. There were no significant differences in the cure rates, 28-day mortality or hospitalization durations between the MEPM monotherapy group and the MEPM plus MNZ group cure rates: 91.2% (83/91) vs. 91.3% (21/23), respectively, p = 0.999; 28-day mortality: 2.2% (2/91) vs. 4.3% (1/23), respectively, p = 0.495; hospitalization durations, median (interquartile range): 18 days (11.5–26.5) vs. 20 days (15.5–32.0), respectively; p = 0.214. Twenty patients were selected for each group using propensity score matching. No significant differences were observed in cure rates, 28-day mortality, or hospitalization durations between the MEPM monotherapy group and the MEPM plus MNZ group cure rates: 85.0% (17/20) vs. 95.0% (19/20), respectively, p = 0.605; 28-day mortality: 10% (2/20) vs. 5% (1/20), respectively, p = 0.999; hospitalization durations, median (interquartile range): 16 days (11.8–24) vs. 20.5 days (16.3–38.3), respectively; p = 0.184. In this single-center retrospective cohort, there was no evidence that adding MNZ to MEPM improved clinical efficacy in empiric antimicrobial therapy with infection-source control in cIAI. Not applicable.

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