Differential Effects of Levofloxacin and Ciprofloxacin on the Risk for Isolation of Quinolone-Resistant Pseudomonas aeruginosa

Abstract

Due to the greater in vitro activity of ciprofloxacin than that of levofloxacin against Pseudomonas aeruginosa , the likelihood of isolating a clinical strain of quinolone-resistant (QR) P. aeruginosa might be greater after exposure to levofloxacin than ciprofloxacin. We examined the risk of isolating QR P. aeruginosa in association with prior levofloxacin or ciprofloxacin exposure. A case-case-control study was conducted. Two groups of cases, one with nosocomial QR P. aeruginosa infections and one with nosocomial quinolone-susceptible (QS) P. aeruginosa infections, were compared to a control group of hospitalized patients without P. aeruginosa infections. Bivariable and multivariable analyses were used to determine risk factors for isolation of QR P. aeruginosa and QS P. aeruginosa . One hundred seventeen QR P. aeruginosa and 255 QS P. aeruginosa cases were identified, and 739 controls were selected. Exposures to ciprofloxacin were similar among all three groups (8% for controls, 9.4% for QR P. aeruginosa cases, and 7.5% for QS P. aeruginosa cases; P ≥ 0.6). Levofloxacin use was more frequent in the QR P. aeruginosa cases than in the controls (35.9% and 22.1%, respectively; odds ratio [OR] = 2.0; 95% confidence interval [CI] = 1.3 to 3.0) and less frequent in QS P. aeruginosa cases (14.1% of QS P. aeruginosa cases; OR = 0.6; 95% CI = 0.4 to 0.9). In multivariable analysis, levofloxacin, but not ciprofloxacin, was a significant risk factor for isolation of QR P. aeruginosa (OR for levofloxacin = 1.7 [95% CI = 1.0 to 2.9]; OR for ciprofloxacin = 1.2 [95% CI = 0.6 to 2.5]). Levofloxacin was associated with a reduced risk of isolation of QS P. aeruginosa (OR = 0.6; 95% CI = 0.4 to 0.9), whereas ciprofloxacin had no significant effect (OR = 1.0; 95% CI = 0.6 to 1.8). In conclusion, the use of levofloxacin, but not ciprofloxacin, was associated with isolation of QR P. aeruginosa .