Background and Importance The appropriate use of antibiotics and their clinical impact is a necessary field of study to address the high incidence of resistance.

Aim and Objectives To analyse the impact of inadequate empirical therapy (IAT) on mortality in patients with Pseudomonas aeruginosa (PA) infection in a tertiary hospital.

Material and Methods Observational, retrospective study of patients with PA infection and treated with previous empirical antipseudomonal antibiotics from 1 January 2021 to 31 October 2021. Variables: gender, age, place of admission, dosing regimen, primary focus of infection and mortality during admission or 30 days after discharge. Definition of IAT: non-adherence to the local guidelines that establish the new EUCAST 2021 dosing criteria to achieve sufficient levels of antibiotics reported as ‘sensitive with increased exposure’ and which, based on the prevalence of multi-resistance in PA, recommends empirical use with biotherapy until the antibiogram is available. Data source: pharmacotherapeutic management softplante (Farmatools®) and electronic medical records. Analysis with SPSS Statistics21®

Results 92 patients were admitted to ICU and 126 to non-ICU (men 67.4% and 69.8% respectively) with a mean age of 62.9±12.5 years in ICU and 71.4±15.3 in non-ICU.

In the ICU the main source of infection was the lung (48.9%), while in the non-ICU the lung and urinary tract were at the same level (29.4% each).

In both groups the use of β-lactams (76.8% ICU and 65.7% non-ICU), followed by aminoglycosides in the ICU (13.5%) and quinolones in the non-ICU (22.5%). The use of monotherapy was higher in the non-ICU than in the ICU (66.9% vs. 49.2%, p<0.001).

The IAT was higher in the non-ICU (67.5% vs. 47.8% ICU p=0.041). In non-ICU, the mortality rate during admission or at 30 days in patients with IAT was 22.4% vs 7.3% with adequate empirical therapy (OR: 3.64; 95% CI 1.01–13.13), this difference being statistically significant. In ICU there were also higher mortality rates in the IAT group (50.0% vs 39.6%), but without statistically significant differences (OR:1.53; 95% CI 0.67–3.49).

Conclusion and Relevance The higher mortality observed in cases of IAT implies the need to work on the adequacy of dosage according to EUCAST criteria and to promote bitherapy until the antibiogram is available.

Conflict of Interest No conflict of interest.