Experimental endocarditis due to Pseudomonas aeruginosa. II. Therapy with carbenicillin and gentamicin.

Rabbits with left-sided endocarditis due to Pseudomonas aeruginosa were treated with a high dose (7.5 mg/kg) of gentamicin for six days, a low dose (5 mg/kg) of gentamicin for six days or two weeks, carbenicillin (400 mg/kg) for six days or two weeks, or a combination of the lower dose of gentamicin and carbenicillin (400 mg/kg) for six days or two weeks. Sterilization of cardiac vegetations was accomplished more effectively in rabbits given the higher dose of gentamicin for six days (44% with sterilized vegetations) or combination therapy for 14 days (64%) than in rabbits given the lower dose of gentamicin or carbenicillin alone for two weeks (23.5% and none, respectively). Combination therapy for two weeks prevented relapse in all of six treated rabbits that were followed after treatment; in contrast, all four animals treated with carbenicillin and four of six animals treated with the lower dose of gentamicin relapsed after two weeks of treatment. Levels of creatinine in serum became elevated in four of nine rabbits that received gentamicin along for two weeks. Therapeutic success was associated with a synergistic antibiotic combination, a peak bactericidal titer in serum of greater than or equal to 1:16, and a high level of gentamicin in serum.