Enhanced activity of beta-lactam antibiotics with amdinocillin in vitro and and in vivo.

An important advantage of antibiotic combinations which can be determined is the increase in spectrum of activity. Ad hoc combinations of amdinocillin with ampicillin, ticarcillin, piperacillin, azlocillin, cefazolin, cefamandole, cefoxitin, and moxalactam in ratios similar to those in serum after parenteral administration of normal dosages of these agents were tested in vitro against over 200 strains of bacteria, including Staphylococcus aureus, Streptococcus faecalis, representative genera of the Enterobacteriaceae, and Pseudomonas aeruginosa. Independent of amdinocillin's activity, it was possible to show marked enhancement of the spectrum of all the beta-lactam agents tested, except moxalactam, against members of the Enterobacteriaceae. Little or no enhancement or antagonism of activity was seen against gram-positive bacteria or P. aeruginosa. The enhancing activity of amdinocillin on three beta-lactam antibiotics, ampicillin, cefazolin, and cefoxitin, was also demonstrated in experimental mouse infections with gram-negative bacteria.