In vivo antibacterial activity of S-3578, a new broad-spectrum cephalosporin: methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa experimental infection models.

The in vivo antibacterial activity of S-3578, a new parental cephalosporin, was compared with those of cefepime, ceftriaxone, ceftazidime, imipenem-cilastatin, and vancomycin. The efficacy of S-3578 against systemic infections caused by methicillin-resistant Staphylococcus aureus (MRSA) SR3637 (50% effective dose [ED(50)], 7.21 mg/kg of body weight) was almost the same as that of vancomycin. In contrast, cefepime and imipenem-cilastatin were less active against this pathogen (ED(50)s, >100 and >100 mg/kg, respectively). S-3578 was the most effective compound against penicillin-resistant Streptococcus pneumoniae SR20946 (ED(50), 1.98 mg/kg). S-3578 (10 mg/kg) induced a significant reduction in the numbers of viable MRSA SR17764 and Pseudomonas aeruginosa SR10396 organisms in polymicrobial pulmonary infections. The therapeutic efficacy of S-3578 was more potent than that of the combination of vancomycin and ceftazidime. High levels of S-3578 were detected in plasma in vivo, and its efficacy against experimentally induced infections in mice caused by MRSA and P. aeruginosa reflected its potent in vitro activity. We conclude that S-3578 is a promising new cephalosporin for the treatment of infections caused by gram-positive and -negative bacteria, including MRSA and P. aeruginosa.