Latamoxef in combination with aminoglycosides against Pseudomonas aeruginosa: similarity with ticarcillin

The in vitro effect of latamoxef against 50 clinical strains of Pseudomonas aeruginosa was compared to that of ticarcillin, both alone and in combination with the aminoglycosides gentamicin, tobramycin and amikacin. Alone, the MIC90 of latamoxef was consistently one-half the MIC90 of ticarcillin. The two antibiotics appeared similar in regard to inoculum effect and bacterial killing. Adding of one-quarter the minimum inhibitory concentration of the aminoglycoside antibiotic to the beta lactam caused reduction in MIC90 of the latter (either ticarcillin or latamoxef) by one-half and decreased the MIC50 by almost one-quarter the concentration required by the beta lactams singly. Therefore, latamoxef singly or in combination with aminoglycosides behaved similarly but was more active than ticarcillin. Using combinations of antibiotics likely to be achieved in the serum of patients, a beneficial in vitro effect (either additive, partially synergistic or synergistic) generally occurred for the beta lactam-aminoglycoside combination if the strain was relatively sensitive to the aminoglycoside used in this combination. It occurred much less frequently for the highly aminoglycoside-resistant isolates.