Pseudomonas aeruginosa bacteremia is associated with a high mortality rate, and meropenem (MEPM) is commonly used to treat it. However, the relationship between the time above the minimum inhibitory concentration (fT_>MIC) of MEPM and its therapeutic efficacy in P. aeruginosa bacteremia has not been explored. This study aimed to investigate this relationship by defining the target % fT_>MIC of MEPM as 75%. The retrospective study spanned 14 years and included hospitalized patients treated with MEPM for P. aeruginosa bacteremia. Monte Carlo simulation was used to calculate the probability of target attainment (PTA) for each patient, and the threshold for a PTA of 75% fT_>MIC associated with in-hospital survival was determined using receiver operating characteristic (ROC) curves. The ROC curve-derived PTA associated with improved in-hospital survival was 65.0%, a significant finding in multivariate logistic regression analysis adjusted for patient background factors (odds ratio: 20.49, 95% confidence interval: 3.02–245.23, p = 0.005). This result suggests a dosing regimen that achieves a PTA of at least 65% when the target fT_>MIC of MEPM for treating P. aeruginosa bacteremia is defined as 75%.

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.