Combined action of carbenicillin and gentamicin on Pseudomonas aeruginosa in vitro.

The minimal inhibitory and minimal bactericidal concentrations of carbenicillin and gentamicin were determined for 10 strains of Pseudomonas aeruginosa isolated from the urinary tract. Combinations of the two drugs were tested for possible enhanced activity. Such enhancement was demonstrated in the inhibitory activity of combinations for eight strains. Striking bactericidal activity against five strains was achieved by the combination, whereas neither drug alone in low dosage was capable of bactericidal action. The possible mode of action and the possible merit of pursuing these preliminary findings are discussed.