Linezolid, critical characteristics

In spite of a constantly expanding information base with the oxazolidinones generally and linezolid specifically, we have elected here to focus on the key characteristics of linezolid. Linezolid is the first member of a new class of antimicrobial agents, the oxazolidinones, to be tested in humans in Phase I, Phase II and Phase III clinical trials. The oxazolidinones have a novel mechanism of action in that they inhibit initiation complex formation in bacterial protein synthesis and, consistent with a novel mechanism of action, they do not exhibit cross-resistance with existing antibacterial agents. Importantly, resistance development as measured in the laboratory occurs very slowly, there is no evidence of rapid resistance development. The spectrum of oxazolidinone activity is principally gram-positive and in vitro studies demonstrate that linezolid is equivalent to vancomycin in vitro. Linezolid is orally as well as intravenously active and orally administered linezolid is as efficacious in mouse models of bacterial disease as is subcutanously administered vancomycin against appropriate pathogens. The exceptional oral behavior of linezolid in mouse models is readily explained by the observation that oral linezolid is 100% bioavilable and that administration of 400- and 600-mg doses of linezolid in humans results in blood level curves which predict that linezolid will be very well suited for bid dosing. Additionally, the blood level concentrations are in significant and very comfortable excess of the MIC90 concentrations for the important gram-positive pathogens for the bulk of the dosing interval.