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277 Colistin versus tigecycline for the treatment of Acinetobacter baumannii and/or carbapenem resistant Enterobacteriaceae infections

Saturday, April 2, 2011
Trinity Ballroom (Hilton Anatole)
Kimberley Ku, BS , Detroit Medical Center, Wayne State University, Detroit, MI
Judy Moshos, MT , Detroit Medical Center, Wayne State University, Detroit, MI
Suchitha Bheemreddy, MD , Detroit Medical Center, Wayne State University, Detroit, MI
Yujing Wang, BS , Detroit Medical Center, Wayne State University, Detroit, MI
Ashish Bhargava , Detroit Medical Center, Wayne State University, Detroit, MI
Michelle Campbell, BA , Detroit Medical Center, Wayne State University, Detroit, MI
Namir Khandker, BS , Detroit Medical Center, Wayne State University, Detroit, MI
Teena Chopra, MD , Detroit Medical Center, Wayne State University, Detroit, MI
Kayoko Hayakawa, MD, PhD , Detroit Medical Center, Wayne State University, Detroit, MI
Odaliz Abreulanfranco, MD , Detroit Medical Center,Wayne State University, Detroit, MI
Paul R. Lephart, PhD , Detroit Medical Center, Wayne State University, Detroit, MI
Jason M. Pogue, PharmD , Detroit Medical Center, Wayne State University, Detroit, MI
Sorabh Dhar, MD , Detroit Medical Center, Wayne State University, Detroit, MI
Keith S. Kaye, MD, MPH , Detroit Medical Center, Wayne State University, Detroit, MI
Dror Marchaim, MD , Detroit Medical Center, Wayne State University, Detroit, MI
Background: Therapeutic options are scarce for the treatment of infections caused by Acinetobacter baumannii or carbapenem-resistant Enterobacteriaceae (CRE).

Objective: The study aim was to compare the efficacy of colistin, an older drug, to tigecycline, a newer drug, for the treatment of these infections.

Methods: A retrospective study was conducted at Detroit Medical Center (DMC), an 8-hospital healthcare system with >2,200 inpatient beds. For calendar year 2009, adult (>18 years) patients with infections due to  A. baumannii or CRE who received ≥2 doses of colistin or tigecycline from 3 days prior to 14 days after their culture date, were studied. Risk factors, time to initiation of appropriate therapy, and outcomes, were abstracted from patient charts and analyzed. Susceptibility to colistin and tigecycline was determined using E-test (AB Biodisk®, Solna, Sweden).

Results: There were 84 patients with infections due to A. baumannii, 12 patients with CRE, and 12 patients with both A. baumannii and CRE co-infection, who met all inclusion criteria. Seventy-one (71) received colistin, 14 received tigecycline, and 23 received both colistin and tigecycline. Seven (7%) isolates were non-susceptible to colistin (mean MIC for the entire cohort was 1.5 ± 3.8 μg/mL) and 79 (82%) to tigecycline (mean MIC for the entire cohort was 5.4 ± 5.5 μg/mL). Patients receiving colistin alone or in combination were more likely to die during their hospitalization than patients receiving only tigecycline (35/94 [37%] vs. 0/14, p=0.005).  However, compared to patients only receiving tigecycline, patients receiving colistin were significantly older (p=0.003), more often had rapidly fatal conditions per McCabe score (p=0.004), and had notable delays in receiving effective antimicrobial therapy (p=0.003 between groups).

Conclusions: Compared to patients who received tigecycline alone, patients who received colistin alone or in combination were elderly and had a high severity of acute illness.  In addition, patients receiving colistin had delays in effective therapy approaching 5 days after culture (compared to ~ 2 days for tigecycline). Although mortality rates were significantly higher among patients receiving colistin as compared to tigecycline, these differences were due, at least in part, to differences in case-mix and severity of underlying illness.