PHILADELPHIA, PA—Initial combination antimicrobial therapy consisting of beta-lactam and aminoglycoside agents was not superior to monotherapy with a beta-lactam agent alone in the treatment of Klebsiella, E. coli, or Enterobacter bacteremia, a study reported at IDWeek 2014.

“There were no differences in 7-day and 30-day mortality between the treatment groups,” reported Nalini Singh, MD, MPH, from The George Washington University, Washington, DC. Dr. Singh and colleagues conducted a retrospective cohort study (2008-2011) in children and adults younger than 21 years of age who were hospitalized with laboratory-confirmed Enterobacteriaceae bacteremia.

Clinical outcome, measured as response to therapy (time to negative blood culture), and 7- and 30-day mortality was compared between patients given monotherapy versus combination therapy. Multidrug resistant (MDR) gram-negative rods were defined as those organisms resistant to at least one agent in three or more antimicrobial categories.    

A total of 289 cases of Enterobacteriaceae gram-negative rod bacteremia were attributable to Klebsiella spp. (27%, of which 14% were MDR), E. coli (25%, of which 15% were MDR), Enterobacter (18%, of which 25% were MDR), and Salmonella, Citrobacter and others (16%).

Of 203 cases (70%) of bacteremia caused by the 3 organisms of interest, 101 (50%) were treated with combination therapy. Patients with cancer were more likely to receive combination therapy (P<0.01), while those with gastrointestinal disease or receiving total parenteral nutrition were more likely to receive monotherapy (P≤0.01 and P=0.02, respectively).

“Patients with prior hospitalization or antibiotics within 30 days of bacteremia episode were more likely to receive combination therapy (P=0.02 and P<0.01, respectively),” Dr. Singh reported.

The study found no differences in time to negative blood culture (mean 3.2 days) based on the treatment group, organism, or resistance pattern.