Bactericidal activity and killing rate of serum in volunteers receiving pefloxacin alone or in combination with ceftazidime, piperacillin or mezlocillin against Pseudomonas aeruginosa.

The activity of the combination of pefloxacin with ceftazidime, piperacillin, or mezlocillin was compared to the activity of the same antibiotics given alone, by measurement of serum bactericidal titres and the rate of killing of ten strains of Pseudomonas aeruginosa. Three groups of five volunteers each received pefloxacin (12 mg/kg iv) with or without ceftazidime, piperacillin or mezlocillin (25 mg/kg iv). Serum samples were obtained at the end of the infusion. The mean serum concentration of pefloxacin at this time was 13.9 mg/l (3.2, S.D.). The activity of each of the three combinations was identical to the corresponding activity of the beta-lactam alone. However, the emergence of resistance to pefloxacin was prevented by ceftazidime (five out of five strains), and piperacillin (two out of five strains). We conclude that combinations of pefloxacin with beta-lactam antibiotics may not increase efficacy against P. aeruginosa.