Association of pharmacokinetic and pharmacodynamic aspects of linezolid with infection outcome.

Linezolid is the first antibiotic of a new class (oxazolidinones). It inhibits protein synthesis by binding to the bacterial 23S ribosomal RNA of the 50S subunit, thus blocking the formation of the functional 70S initiation complex, but it does not inhibit peptidyl transferase. Therefore, its mechanism of action is unique and cross resistance is unlikely to occur; however, resistant strains have already been reported, but the rate of resistance is low in surveillance programs. Linezolid has a favorable pharmacokinetic profile. It is rapidly absorbed when administered orally, and it is 100% bioavailable, thus allowing early switch from intravenous to oral administration. The maximum plasma concentration (range between 13.1+/-1.8 to 19.5+/-4.5 microg/ml according to the route of administration, studied population and dosages administered to subjects) is achieved 1-2 hours after the first dosage. It penetrates readily to most tissues of the human body at concentrations much higher than that of the minimal inhibitory concentrations of the targeted pathogens. It is metabolized by oxidation in two major inactive metabolites and is eliminated mainly through the kidneys. Linezolid is bacteriostatic for staphylococci and enterococci but bactericidal for pneumococci and kills bacteria in a time-dependent fashion. It has been studied in several randomized controlled trials and has been approved for the treatment of patients with Gram positive bacterial infections (community-acquired and nosocomial pneumonia, skin and soft tissue infections, and infections due to vancomycin-resistant enterococci) including these due to multidrug-resistant strains. Careful and judicious use is warranted to preserve the activity of this important antibiotic.