[Antibacterial activities of combination uses of isepamicin and beta-lactams in vitro against clinically isolated strains. Part 3. The results against Pseudomonas aeruginosa].

We investigated antibacterial activities of combination uses of isepamicin (ISP) and beta-lactams in vitro against Pseudomonas aeruginosa, and the following conclusions were obtained. 1. ISP + piperacillin, ISP + ceftazidime, ISP + aztreonam, ISP + imipenem and ISP + panipenem against P. aeruginosa showed strong combined effects. 2. The minimum inhibitory concentrations (MICs) of these combinations were low and dependent on concentrations of ISP. And strong antibacterial activities were observed at ISP concentrations of sub-MIC levels. These results were similar to the results of previous reports, parts 1 and 2. 3. Concentrations of ISP sufficient to lower MIC90 values when by combined with beta-lactam agents were 4 approximately 8 micrograms/ml. These effects made it possible to lower the ISP dose to 400 mg at a single dose and the enhancement of activities by combinations resulted in strong antibacterial activities against multiple drug resistant stains at sub-MIC levels of ISP. Strong antibacterial activities were also obtained against beta-lactams-resistant strains of ISP-susceptible strains when ISP was combined with beta-lactam agents. 4. All results reported in parts 1 approximately 3 indicated that no antagonisms were produced by combining ISP + penicillins, ISP + cephems, ISP + monobactams and ISP + carbapenems against Staphylococcus aureus, Enterobacteriaceae and P. aeruginosa. These combinations showed strong antibacterial activities that were enhanced synergistically with wider spectra.