Use of new beta-lactam antibiotics in intraabdominal surgery.

Infections after gastrointestinal surgery may involve both Gram-positive and Gram-negative aerobic and anaerobic microorganisms. Although the broadspectrum cephalosporins are active against most Gram-positive and Gram-negative bacteria, many of these agents are ineffective against Bacteroides fragilis, many clostridia and some strains of Escherichia coli, Pseudomonas aeruginosa and enterococci. These bacteria are frequently found in intraabdominal infections. A major reason for this inefficacy is susceptibility to beta-lactamases. The new beta-lactam antibiotics--cephamycins, third generation cephalosporins, carbapenems, acyl ureidopenicillins and monobactams--are all more or less beta-lactamase stable. The beta-lactamase inhibitors combined with a beta-lactam antibiotic give a broad antibacterial spectrum. Most of these compounds are non-toxic or relatively atoxic and, with the exception of the monobactams, they can be used as a monotherapy in many infections derived from the gastrointestinal tract. Antibiotic prophylaxis in colorectal surgery offers a clinical model for the study of the benefit and risks of new beta-lactam antibiotics. Most infections are derived from the gastrointestinal endogenous microflora. The study of the impact of different antibiotics on the colonic microflora indicates the risk of bacterial resistance, superinfection, antibiotic associated diarrhoea and pseudomembranous colitis. Data obtained from such studies with the new beta-lactam antibiotics are compared to the results from controlled clinical trials with these antibiotics in this review article.