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

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] (cid:1) 2.0; 95% conﬁdence interval [CI] (cid:1) 1.3 to 3.0) and less frequent in QS P. aeruginosa cases (14.1% of QS P. aeruginosa cases; OR (cid:1) 0.6; 95% CI (cid:1) 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 (cid:1) 1.7 [95% CI (cid:1) 1.0 to 2.9]; OR for ciproﬂoxacin (cid:1) 1.2 [95% CI (cid:1) 0.6 to 2.5]). Levoﬂoxacin was associated with a reduced risk of isolation of QS P. aeruginosa (OR (cid:1) 0.6; 95% CI (cid:1) 0.4 to 0.9), whereas ciproﬂoxacin had no signiﬁcant effect (OR (cid:1) 1.0; 95% CI (cid:1) 0.6 to 1.8). In conclusion, the use of levoﬂoxacin, but not ciproﬂoxacin, was associated with isolation of QR P. aeruginosa were determined by comparing patients with QR P. aeruginosa to uninfected controls. In the second analysis, risk factors for isolation of QS P. aeruginosa were identiﬁed by comparing patients with QS P. aeruginosa to the same group of uninfected controls. By comparing and contrast-ing these two models, variables uniquely associated with the isolation of QR P. aeruginosa were determined (6, 7, 11–13). Data Bivariable analyses categorical signed-rank test contin-uous logistic regression, two multivariable models were constructed, one predictors of nosocomial isolation of QR P. aeruginosa and the other including predictors of nosocomial isolation of QS P. aeruginosa . The primary objective of these multivariable analyses to assess the independent impact of ciproﬂoxacin and levoﬂoxacin on the risk of isolation of QR P. aeruginosa and QS P. aeruginosa while controlling for potential confounders. The secondary objec- tive of these analyses was to identify other independent predictors of QR P. aeruginosa or QS P. aeruginosa . In addition to ciproﬂoxacin and levoﬂoxacin use, the candidate for in the logistic models all variables with P values of in bivariable A stepwise procedure was ﬁnal ﬁnal