Mechanism of action and in vitro and in vivo activities of S-6123, a new oxazolidinone compound.

The in vitro activity of S-6123, a synthetic antimicrobial compound of the new oxazolidinone series, was compared with those of other orally administered agents against 328 clinical isolates. The compound was moderately active (MICs, 16 to 64 micrograms/ml) against 90% of staphylococci, nonenterococcal streptococci, and Haemophilus influenzae, including strains resistant to beta-lactam antibiotics. S-6123 was minimally active against enterococci and facultative gram-negative bacilli. Nevertheless, the compound had significant activity in a lethal rat Escherichia coli peritonitis model at serum concentrations of one-tenth the MIC against the infecting organism. The drug demonstrated only bacteriostatic activity against susceptible organisms. Studies to define the mechanism of antibacterial action revealed that S-6123 inhibited ribosomal protein synthesis without inhibiting DNA or RNA synthesis. This compound represents a new series of antibacterial agents not related to any other antibacterial compound of natural or synthetic origin.