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Pharmacology: Pharmacodynamics: Antimicrobial Action: Linezolid is an oxazolidinone antibacterial with activity against a range of aerobic Gram-positive bacteria including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. It is less active against Gram-negative bacteria, but has some in-vitro activity against Haemophilus influanzae, spp., (Branhamella catarrhalis) and Pasteurella spp. It is not active against Acinetobacter spp., Enterobacteriaceae, or Pseudomonas spp. Oxazolidinone antibacterials are bacteriostatic and act by inhibition of ribosomal protein synthesis. Cross-resistance between oxazolidinones and other classes of antibacterial is considered unlikely. Resistant strains of enterococci and methicillin-resistant Staph. aureus have been reported.
Pharmacokinetics: Linezolid is rapidly and extensively absorbed after oral doses and maximum plasma concentrations are achieved after 1 to 2 hours. It is about 31% bound to plasma proteins. Linezolid is reported to be distributed into bone, fat, lungs, muscle, skin blister fluids, and into the CSF. It is metabolised mainly by oxidation to 2 main inactive metabolites, the hydroxyethyl glycine metabolite (PNU-142586) and the aminoethoxyacetic acid metabolite (PNU-142300); other minor inactive metabolites have also been identified. About 40% of a dose is excreted in the urine as PNU-142586, 30% as linezolid, and 10% as PNU-142300. Small amounts of metabolites are excreted in the faeces. The elimination half-life of linezolid is about 5 to 7 hours. Children exhibit more rapid clearance of linezolid than adults; half-life is reported to range from about 2 to 4 hours, increasing with age.
