Clinical implications of cefoperazone–sulbactam MIC values in Pseudomonas aeruginosa bloodstream infections: a multicentre study

Background Cefoperazone/sulbactam (CPZ/SUL, 1:1) is used for Pseudomonas aeruginosa bloodstream infections (BSIs); however, its clinical minimum inhibitory concentration (MIC) breakpoint remains undefined. This study aimed to evaluate the association between CPZ/SUL MIC values and clinical outcomes. Methods We retrospectively analysed 122 adults with P. aeruginosa BSIs treated with CPZ/SUL (1:1) for ≥3 days across eight Taiwanese medical centres (July 2017−May 2024). MICs were determined using agar dilution, and outcomes were categorized as favourable (cure/improvement) or poor (failure/mortality). Isolate susceptibilities to other agents were also evaluated. Results Overall, 76.2% achieved favourable outcomes. Patients with MICs ≤16 mg/L had significantly higher favourable rates than those with MICs ≥32 mg/L (81.0% versus 54.5%; P = 0.013). This association remained significant across all hierarchical models, including the fully adjusted model (aOR 2.74, 95% CI 1.44–5.25). Pneumonia-associated BSIs had lower favourable outcomes (64.1%). Among all isolates, 82% exhibited MICs ≤16 mg/L. Carbapenem-resistant P. aeruginosa (CRPA) accounted for 18% of cases, with 59.1% showing favourable responses to CPZ/SUL. Conclusions Lower CPZ/SUL MIC values were independently associated with more favourable clinical outcomes in patients with P. aeruginosa BSIs. These findings support the clinical relevance of MIC stratification and may inform antimicrobial stewardship and individualized treatment decisions.