The activity of ceftazidime, other beta-lactams, and aminoglycosides against Pseudomonas aeruginosa.

The inhibitory and bactericidal activities of ceftazidime, cefoperazone, ceftriaxone, piperacillin, and five aminoglycosides were determined against 50 tobramycin-susceptible and 25 multidrug-resistant isolates of Pseudomonas aeruginosa. Ceftazidime was the most active beta-lactam and tobramycin the most active aminoglycoside. The combination of piperacillin and tobramycin was synergistic in most cases. The combination of cephalosporin and tobramycin showed mostly addition or indifference, as did combination of two beta-lactams. No antagonism was observed.