Abstract

Abstract Among consecutive patients with multidrug-resistant Pseudomonas aeruginosa bacteremia or pneumonia we found those treated with ceftazidime-avibactam were more likely to develop resistance (defined as ≥4-fold increased MIC) than those treated with ceftolozane-tazobactam (40% vs 10%; P = .002). Ceftazidime-avibactam resistance was associated with new mutations in ampC and efflux regulatory pathways.