Emergence of antibiotic-resistant Pseudomonas aeruginosa: Comparison of risks associated with different antipseudomonal agents

Pseudomonas aeruginosa is a leading cause of nosocomial infections. The ris k of emergence of antibiotic resistance mag vary with different antibiotic treatments. To compare the risks of emergence of resistance associated with four antipseudomonal agents, ciprofloxacin, ceftazidime, imipenem, and pip eracillin, we conducted a cohort study, assessing relative risks for emerge nce of resistant P. aeruginosa in patients treated with any of these drugs. A total of 271 patients (followed for 3,810 days) with infections due to P . aeruginosa were treated with the study agents. Resistance emerged in 28 p atients (10.2%). Adjusted hazard ratios for the emergence of resistance wer e as follows: ceftazidime, 0.7 (P = 0.4); ciprofloxacin, 0.8 (P = 0.6); imi penem, 2.8 (P = 0.02); and piperacillin, 1.7 (P = 0.3), Hazard ratios for e mergence of resistance to each individual agent associated with treatment w ith the same agent were as follows: ceftazidime, 0.8 (P = 0.7); ciprofloxac in, 9.2 (P = 0.04); imipenem, 44 (P = 0.001); and piperacillin, 5.2 (P = 0. 01). We concluded that there were evident differences among antibiotics in the likelihood that their use mould allow emergence of resistance in P, aer uginosa. Ceftazidime was associated with the lowest risk, and imipenem had the highest risk.