Abstract Background Guidelines suggest dual anti-pseudomonal therapy for empiric treatment of pneumonia caused by Gram-negative bacteria in ICU patients. Additionally, consideration of local susceptibility data and patient-specific risk factors for resistance is recommended for selecting optimal empiric regimens. However, data assessing how to best do this are lacking, and it is unclear whether a local susceptibility data-based or a patient specific risk factor-based approach will better drive appropriate empiric treatment. This study aims to compare these two strategies. Methods This retrospective study was divided into two periods. In period I, Gram-negative respiratory cultures from ICU patients were used to develop unit-specific combination antibiograms, and individual patient charts were reviewed to assess the impact of risk factors on antimicrobial susceptibility to develop a risk-factor based treatment algorithm. Optimal empiric regimens based on these two strategies were then defined. In period II, these regimens were hypothetically applied to patients to compare rates of appropriate empiric therapy and overuse by the two methods. Results Risk factor-based regimens had a higher appropriateness rate compared to regimens derived from antibiograms (89.9% vs 83.7%). Additionally, applying antibiogram based regimens resulted in a higher prevalence of antibiotic overuse than a patient-specific risk factor based approach (69.8% vs. 40.3%), with excess overuse driven by a higher frequency of unnecessary use of combination therapy. Conclusion Both strategies provided high rates of appropriateness in empiric antibiotic selection. However, the patient-specific risk factor-based approach demonstrated a higher rate of appropriate therapy and offered advantages in reducing rates of unnecessary combination therapy.
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