Linezolid, a synthetic oxazolidinone antimicrobial, shows a wide spectrum against Gram-positive bacteria andmultidrug-resistant bacteria such as anaerobes, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, penicillin-resistant pneumococci and streptococcus [1,2].

Oxazolidinones could inhibit protein synthesis by binding to a site on the bacterial 23S ribosomal RNA of the 50S subunit and prevent the formation of a functional 70S-initiation complex. Linezolid is also a weak, nonselective and reversible inhibitor of monoamine oxidase [2].

In Vitro: Linezolid was a potent inhibitor of cell-free transcription-translation in E. coli. IC50 was 1.8 mM[3]. linezolid MICs vary slightly owing to the different test method and laboratory. The MIC values were between 0.5 and 4 mg/L for streptococci, enterococci and staphylococci [4].

Clinical Trials: Linezolid is fully bioavailable following oral administration, with maximum plasma linezolid concentrations achieved between 1 and 2 hours after oral administration. The elimination half-life of linezolid is 5–7 hours, and twice-daily administration of 400–600mg provides steady-state concentrations in the therapeutic range[5].

In clinical trials involving hospitalised patients with skin/soft tissue infections (predominantly S. aureus), intravenous/oral administration of linezolid (up to 1250 mg/day) produced clinical success in > 83% of individuals. In patients with community-acquired pneumonia, success rates were > 94%[6]. Linezolid could also be used in patients with nosocomial pneumonia[7].Linezolid appears to be well tolerated and the most common side effects is gastrointestinal disturbances [6].

References:
[1] Tsiodras S, Gold H S, Sakoulas G, et al.  Linezolid resistance in a clinical isolate of Staphylococcus aureus[J]. The Lancet, 2001, 358(9277): 207-208.
[2] Swaney S M, Aoki H, Ganoza M C, et al.  The oxazolidinone linezolid inhibits initiation of protein synthesis in bacteria[J]. Antimicrobial agents and chemotherapy, 1998, 42(12): 3251-3255.
[3] Shinabarger D L, Marotti K R, Murray R W, et al.  Mechanism of action of oxazolidinones: effects of linezolid and eperezolid on translation reactions[J]. Antimicrobial agents and chemotherapy, 1997, 41(10): 2132-2136.
[4] Livermore D M.  Linezolid in vitro: mechanism and antibacterial spectrum[J]. Journal of antimicrobial chemotherapy, 2003, 51(suppl 2): ii9-ii16.
[5] Stalker D J, Jungbluth G L.  Clinical pharmacokinetics of linezolid, a novel oxazolidinoneantibacterial[J]. Clinical pharmacokinetics, 2003, 42(13): 1129-1140.
[6] Clemett D, Markham A.  Linezolid[J]. Drugs, 2000, 59(4): 815-827.
[7] Wunderink R G, Cammarata S K, Oliphant T H, et al.  Continuation of a randomized, double-blind, multicenter study of linezolid versus vancomycin in the treatment of patients with nosocomial pneumonia[J]. Clinical therapeutics, 2003, 25(3): 980-992.