An evaluation of the activity of cephalosporins against Pseudomonas aeruginosa.

We investigated the in-vitro activity of 14 antibiotics against 200 distinct isolates of Pseudomonas aeruginosa obtained from intensive care patients. Ceftazidime was the most active beta-lactam and 16 mg/l inhibited 88% of the strains. Of 55 two-drug combinations, ceftazidime plus tobramycin was the most effective and 98.5% of strains were sensitive. Synergism between these two drugs was demonstrated for 12 of the 23 strains tested. Ceftazidime-inactivating enzymes may be induced in Ps. aeruginosa by cefoxitin.