Although combinations of gentamicin and carbenicillin have acted synergistically on Pseudomonas aeruginosa in vitro, in this study there was no significant evidence that they did so in vivo when given subconjunctivally to rabbits with Pseudomonas keratitis. The clinical and bacteriological effects of gentamicin (10 mg), carbenicillin (114 mg), and polymyxin B sulfate (5 mg) were essentially the same. Combinations of gentamicin and carbenicillin were at least as effective as each antibiotic given alone.
Bohigian G, Okumoto M, Valenton M. Experimental Pseudomonas KeratitisTreatment With and Evaluation of Carbenicillin and Gentamicin in Combination. Arch Ophthalmol. 1971;86(4):432-437. doi:10.1001/archopht.1971.01000010434013