In vitro and in vivo properties of Ro 63-9141, a novel broad-spectrum cephalosporin with activity against methicillin-resistant staphylococci

Ro 63-9141 is a new member of the pyrrolidinone-3-ylidenemethyl cephem seri es of cephalosporins. Its antibacterial spectrum was evaluated against sign ificant gram-positive and gram-negative pathogens in comparison with those of reference drugs, including cefotaxime, cefepime, meropenem, and ciproflo xacin, Ro 63-9141 showed high antibacterial in vitro activity against gram- positive bacteria except ampicillin-resistant enterococci, particularly van comycin-resistant strains of Enterococcus faecium. Its MIC at which 90% of the isolates tested were inhibited (MIC90) for methicillin-resistant Staphy lococcus aureus (MRSA) was 4 mug/ml. Ro 63-9141 was bactericidal against MR SA, Development of resistance to the new compound in MRSA was not observed. Ro 63-9141 was more potent than cefotaxime against penicillin-resistant St reptococcus pneumoniae (MIC90 = 2 mug/ml). It was active against ceftazidim e-susceptible strains of Pseudomonas aeruginosa and against Enterobacteriac eae except Proteus vulgaris and some isolates producing extended-spectrum b eta -lactamases. The basis for the antibacterial spectrum of Ro 63-9141 lie s in its affinity to essential penicillin-binding proteins, including PBP 2 ' of MRSA and its stability towards p-lactamases, The in vivo findings were in accordance with the in vitro susceptibilities of the pathogens. These d ata suggest the potential utility of Ro 63-9141 for the therapy of infectio ns caused by susceptible pathogens, including MRSA. Since insufficient solu bility of Ro 63-9141 itself precludes parenteral administration in humans, a water-soluble prodrug, Ro 65-5788, is considered for development.