Comparative activity and β-lactamase stability of carbenicillin, ticarcillin, azlocillin, mezlocillin and cefotaxime

The inhibitory activities of azlocillin, mezlocillin, cefotaxime, carbenicillin and ticarcillin were compared using 150 strains of Pseudomonas aeruginosa. Azlocillin was the most active antibiotic and mezlocillin the least active. The MICs of azlocillin, mezlocillin, cefotaxime and carbenicillin were measured using ten further strains of Ps. aeruginosa producing known β-lactamases. Serum levels of these antibiotics were also measured between 1 and 6 h after a single dose to volunteer patients. Although cefotaxime was stable to all β-lactamases tested the activity of azlocillin was thought to be superior since it combined low MICs with high blood levels and stability to most β-lactamases.