Marschall et al evaluated the adequacy of empirical antibiotic therapy for Gram-negative bacteremia in non-ICU patients. The authors are from Washington University and BJC Healthcare in St. Louis.

Patient selection: Gram-negative bacteremia


Time periods for judging adequacy of therapy:

(1) within 24 hours of blood culture sampling

(2) within 24 hours of notification of bacterial growth

(3) within 24 hours of bacterial identification

(4) within 24, 48 hours or 72 from the time of notification for susceptibility results


In traditional microbiology a blood culture may turn positive within a few to 48 hours, with an additional 24 hours required for identification and susceptibility testing. Molecular methods will reduce the time intervals involved.


Inadequate empirical antibiotic therapy was defined as:

(1) one of the following:

(1a) no antibiotic therapy

(1b) no antibiotic that matches the susceptibility pattern for the isolate

(2) within 24 hours of the initial positive blood culture


Factors that can cause problems for empirical prescribing:

(1) polymicrobial bacteremia

(2) an isolate that is antibiotic resistant


Since susceptibility results might not be known for 48 hours after the blood culture is collected then failure to cover a resistant organism would occur with some frequency.

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