title: Optimizing empirical antimicrobial therapy for infection due to gram-negative pathogens in the intensive care unit: utility of a combination antibiogram.
abstract: OBJECTIVE
  To determine whether the use of dual antimicrobial therapy based on the results of a combination antibiotic susceptibility report (antibiogram) increases the likelihood of selecting adequate empirical coverage in critically ill patients with infection due to potentially resistant gram-negative pathogens.
  
  
  METHODS
  Retrospective data analysis.
  
  
  METHODS
  Urban academic medical center.
  
  
  METHODS
  An analysis of culture results and susceptibility data from intensive care unit patients determined by the clinical microbiology laboratory was performed. The proportion of 5 common gram-negative pathogens susceptible to monotherapy with 1 of 3 antipseudomonal antibiotics (piperacillin-tazobactam, ceftazidime, or imipenem) was compared with the proportion susceptible to each of these 3 "backbone" agents plus 1 of 4 additional antimicrobial agents used in combination.
  
  
  RESULTS
  More than 5,000 clinical isolates were examined. When all isolates recovered during the entire study period were included, the addition of any of the second antibiotics studied to each of the 3 backbone agents significantly increased the likelihood of covering the causative pathogen (P < .01 for each). The benefit of combination therapy was variable when results for each of the 5 organisms were examined individually. When temporal trends in susceptibility were examined, the decrease in the proportion of organisms susceptible to monotherapy was statistically significant for both imipenem and ceftazidime (P < .01).
  
  
  CONCLUSIONS
  Reporting antibiotic susceptibility data in the form of a combination antibiogram may be useful to clinicians who are considering empirical antimicrobial therapy in the intensive care unit.
authors.affiliation: Section of Infectious Diseases, University of Chicago Medical Center, Chicago, Illinois 60637, USA. Jennifer.Christoff@uchospitals.edu
authors.forename: Jennifer
authors.initials: J
authors.lastname: Christoff
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Tolentino
authors.forename: Emily
authors.initials: E
authors.lastname: Mawdsley
authors.forename: Scott
authors.initials: S
authors.lastname: Matushek
authors.forename: David
authors.initials: D
authors.lastname: Pitrak
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Weber
mesh_terms: D000046:Academic Medical Centers; D000890:Anti-Infective Agents / Q000627:therapeutic use*; D002641:Chicago; D004359:Drug Therapy, Combination; D006088:Gram-Negative Aerobic Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D016905:Gram-Negative Bacterial Infections / Q000188:drug therapy*; D006801:Humans; D007362:Intensive Care Units; D008826:Microbial Sensitivity Tests; D012189:Retrospective Studies
chemical_list: D000890:Anti-Infective Agents