Comparison of antibiotic regimens for treatment of experimental pneumonia due to Pseudomonas

The high mortality associated with pneumonia due to Pseudomonas aeruginosa prompted a comparative trial of several currently available antibiotic regimens for this infection in a guinea pig model. Normal guinea pigs receiving an intratracheal challenge of 10(8) colony-forming units of Pseudomonas routinely died within 3-48 hr when treated with saline injections. Treatment with carbenicillin or ticarcillin did not affect this uniformly fatal outcome. Groups of animals treated with gentamicin or tobramycin had survival rates of 39% and 67%, respectively. The addition of either carbenicillin or ticarcillin to an aminoglycoside failed to enhance further the survival rates or durations of survival after infection. These survival data were supported by studies showing superior clearance of viable Pseudomonas from lung tissues in aminoglycoside-treated animals chosen at random for sacrifice 3 hr after infection. Thus, in animals experimentally challenged with P. aeruginosa to cause pneumonia and in which only a single isolate of Pseudomonas was evaluated, protection from pulmonary infection was best provided by an aminoglycoside rather than by a beta-lactam antibiotic.