Background and Importance Bacteremia is a major cause of sepsis and is associated with high morbidity and mortality. Suboptimal antibiotic dosing in the bacteraemic population has previously been associated with poorer outcomes in the Emergency departments (ED).

Aim and Objectives This study has been designed to analyse clinical outcomes in patients with bacteraemia when receiving suboptimal antibiotic dosing (SAD).

Material and Methods Observational, retrospective cohort study performed in a third-level hospital in Spain. The population studied included patients admitted in an ED with positive blood cultures for true pathogenic microorganisms (November 2021 to June 2022). SAD was defined according to Stanford Severe Sepsis and Septic Shock Antibiotic Guide (2020), except for ceftriaxone, in which we used the recommendation of Aaron J. Heffernan et al, 2020 (2g/24h). Data were collected on demographics, microorganisms responsible for the infection, focus of infection, antibiotics and doses used and outcomes in terms of 30-day mortality.

Results A total of 442 patients with bacteremia caused by a microorganism susceptible to the antibiotic prescribed in the ED were evaluated (Mean age: 73±15 years, 54% male), being 54 (12%) considered as SAD. From these patients, 24 infections (44%) were caused by E.coli, being the main focus the urinary tract (n=29, 54%). The most frequently SAD treatments were beta-lactams (n=35, 65%), followed by carbapenems (n=17, 32%), vancomycin (n=8, 15%) and aminoglycosides (n=5, 9%). Among beta-lactams, ceftriaxone was prescribed in SAD (1g/24h) in 8 patients (22%); within carbapenems, meropenem was usually prescribed (without loading dose) adjusted to kidney impairment in the moment of admission. Patients who received SAD presented a higher 30-mortality than those who received an appropriate dosing (22% vs 7%; p=0.001).

Conclusion and Relevance SAD in bacteraemic patients in the ED is 12%, being associated with higher risk of mortality. Beta-lactams and carbapenems are the most prescribed antibiotics in bacteraemia to cover gram-negative spectrum. A possible explanation for SAD in the ED might be that antibiotics are adjusted according to renal function in the moment of admission. We don’t recommend adjusting doses of antibiotics during the first 24–48h of treatment in order to reduce the risk of SAD.

Conflict of Interest No conflict of interest.