Companies are, in fact, developing new antibiotics. Many are just variations on existing drugs. Linezolid is the first in a completely new class of antibiotics known as oxazolidinones.

Discovered in 1989, oxazolidinones have demonstrated significant in vitro activity against such gram positive bacterial pathogens as S. aureus (including methicillin-resistant strains), S. epidermis (also including strains that are methicillin-resistant), S. pneumoniae (including penicillin and cephalosporin-resistant isolates), Enterococcus faecalis and vancomycin-resistant Enterococcus. Structurally, this new class of antibiotics has a five-membered heterocyclic ring system.

Linezolid targets an early stage of a bacterium's protein synthesis cycle. By binding specifically to the 50S ribosomal subunit, it inhibits bacterial protein synthesis. Other antibiotics sabotage later stages in the process bacteria use, to make proteins. Linezolid's unique mechanism of action suggests that cross-resistance between it and other antibiotics is unlikely to occur. Specifically, cross-resistance with antibiotics that inhibit ribosomal protein synthesis has not been observed (15) and may be less likely to occur.

Recent studies of phase II trials have shown that linezolid, shown to have equal bioavailability in IV and oral formulations, is highly effective in treating community-acquired pneumonia caused by S. pneumoniae, as well as complicated and uncomplicated skin and soft tissue infections caused by S. epidermidis, S. aureus, and Enterococcus. Linezolid is now in phase III clinical trials for the treatment of community-acquired and hospital-acquired pneumonia, uncomplicated and complicated skin and soft-tissue infections, and other infections, such as bacteremia, caused by gram-positive pathogens.

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