Fosfomycin in Complicated Intra-Abdominal Infections in an Intensive Care Setting: Does It Improve the Outcome? A Retrospective Observational Study

<b>Background</b>: Intra-abdominal infection (IAI) is a challenging condition that needs both medical and surgical treatment and it is still associated with high morbidity and mortality rates. Fosfomycin is approved for use in combination therapy for IAIs. The aim of this study was to evaluate the impact of intravenous fosfomycin addition in a combination regimen for IAI treatment in an intensive care setting. <b>Methods</b>: We performed a retrospective, observational, monocentric study. We enrolled patients admitted to the ICU with IAIs from April 2022 to June 2024. Patients were divided into two groups: Group A, standard treatment; and Group B, combination therapy including fosfomycin. Primary endpoints were clinical response at 7 days and in-hospital mortality; moreover, a risk factor analysis for mortality was also performed. <b>Results</b>: In total, 104 patients were enrolled, 85 in Group A, and 19 in Group B. Groups were homogenous in regard to demographics, but clinical condition was slightly worst in Group B. Source control < 24 h was performed in 69.6% and 33.3% cases in Group A and Group B, respectively (<i>p</i> = 0.017). Clinical response on day 7 (81.2% vs. 73.7%, <i>p</i> = 0.675) and in-hospital mortality (27.1% vs. 47.2%, <i>p</i> = 0.145) were comparable. Univariate and multivariate analysis highlighted Charlson Comorbidity Index (CCI) (<i>p</i> = 0.04) and septic shock (<i>p</i> = 0.029) as risk factors, and effective empirical therapy (<i>p</i> = 0.04) as the protective factor; fosfomycin was not directly associated with outcome improvement. <b>Conclusions</b>: The outcome was comparable between groups; clinicians preferred to administer a combination regimen including fosfomycin in patients with statistically significant greater severity of illness and without early source control.