Azlocillin and mezlocillin: new ureido penicillins

The activity of azlocillin and mezlocillin, new semisynthetic ureido penicillins, was investigated and compared with that of other known beta-lactam antibiotics. At a concentration of 25 mug/ml, azlocillin inhibited 74% of Enterobacter, 97% of Proteus mirabilis, 64% of Citrobacter, 91% of Pseudomonas aeruginosa, and 82% of Bacteroides strains tested. Mezlocillin inhibited 86% of Shigella, 96% of Enterobacter, 80% of indole-positive Proteus, 88% of Bacteroides, and 63% of Pseudomonas strains tested. Azlocillin was more active against Pseudomonas than was ticarcillin, carbenicillin, or mezlocillin. Mezlocillin was more active than carbenicillin and ampicillin against Escherichia coli, Klebsiella, Enterobacter, Citrobacter, Acinetobacter, Serratia, and Bacteroides. Azlocillin and mezlocillin were less active than cefazolin against beta-lactamase-producing E. coli and Klebsiella strains but more active than cefazolin against Enterobacter, indole-positive Proteus, Acinetobacter, Citrobacter, and Serratia strains. Both compounds showed activity equivalent to that of cefoxitin against Bacteroides isolates. Both agents were destroyed by many of the beta-lactamases from gram-negative organisms.