Intravenous Fosfomycin as Adjunctive Therapy for Gram-Negative Bacteria Bloodstream Infections: A Propensity Score Adjusted Retrospective Cohort Study

: The role of intravenous fosfomycin (iv-FOS), as a part of combination therapy for Gram-negative bacteria bloodstream infections (GNB-BSI), needs to be evaluated in clinical practice as in vitro data show a potential efficacy. : All consecutive patients with a GNB-BSI from January 1st, 2021, to April 1st, 2023, were included. Primary outcome was 30-day mortality. A Cox- regression analysis was used to identify predictors of mortality. Moreover, an inverse-probability of treatment-weighting (IPTW) analysis was also performed. : Overall, 363 patients were enrolled: 211 (58%) males, with a median (q1-q3) age of 68 (57-78) years, and a median Charlson-comorbidity index of 5 (3-7). At GNB-BSI onset, median SOFA score was 5 (2-7), 122 (34%) presented with septic shock. Pathogens involved were principally K. pneumoniae (42%), E. coli (28%), and P. aeruginosa (17%); of them 36% were carbapenem-resistant. The therapy included carbapenems (40%), cephalosporins (37%) and beta-lactams/beta-lactamases-inhibitors (19%); combination with iv-FOS was used in 98 (27%) cases at a median dosage of 16 (16-18) gr/daily. Use of iv-FOS was not associated with reduced crude mortality (21% vs 29%, p-value=0.147). However, at multivariable Cox-regression combination therapy with iv-FOS resulted protective for mortality (aHR=0.51, 95%CI=0.28-0.92), but not other combo-therapies (HR=0.69, 95%CI=0.44-1.16). This result was also confirmed at the IPTW-adjusted-Cox-model (aHR=0.52, 95%CI=0.31-0.91). Subgroup analysis suggested a benefit in severe infections (SOFA>6, PITT≥4) and when iv-FOS was initiated within 24 hours from GNB-BSI onset. : Fosfomycin in combination therapy for GNB-BSI may have a role to improve survival. These results justify the development of further clinical trials.