Calculated empiric antimicrobial therapy for mixed surgical infections.

In acute life-threatening surgical infections requiring immediate institution of antimicrobial therapy before bacteriological results are available, antibiotic treatment must be empiric. For best efficacy a more sophisticated form of empiric therapy is offered, termed calculated antibiotic therapy (CAT). Calculated antibiotic therapy requires consideration of a) typical bacterial spectrum; b) bacterial pathogenicity and synergism; c) antibacterial concentrations at the site of infection; d) toxicity and adverse effects; e) interaction with immune response; and f) results of properly conducted trials. Intraabdominal infections are used as an example here to assess the efficacy of clinically used cephalosporins and penicillins for determination of calculated antibiotic therapy. CAT identifies Escherichia coli and Bacteroides fragilis as the most important pathogens for intraabdominal infections and determines the most effective antibiotics at the tissue breakpoint, which is defined as the minimal concentration maintained for more than 90% of the dosage interval period at the infected tissues. At the tissue breakpoint calculated antibiotic therapy identifies cefotaxime-generation cephalosporins to be fully (100%) active against the most important aerobic pathogen E. coli and metronidazole as fully active against the important obligate anaerobe B. fragilis. Calculated antibiotic therapy becomes relatively important, since impeccably controlled clinical therapeutic trials as a foundation for therapy are rarely published.