Linezolid

Linezolid is an antibiotic in the oxazolidinone class used to treat infections caused by Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci. It is available in intravenous and oral forms with high oral bioavailability.

Mechanism: Linezolid binds to the 50S ribosomal subunit, blocking formation of the initiation complex and inhibiting protein synthesis. It is generally bacteriostatic against most pathogens, with bactericidal activity reported for certain Gram-positive species in some settings.

Spectrum and indications: Active mainly against Gram-positive bacteria; little activity against Gram-negative organisms. Used for complicated skin and soft tissue infections and for certain pneumonias, including those caused by MRSA, and for some VRE infections.

Pharmacokinetics and administration: 100% oral bioavailability; IV and oral forms are interchangeable. Common dosing is 600 mg every 12 hours for many infections; renal impairment may require adjustments. Metabolized by non-enzymatic oxidation to inactive metabolites; excreted in urine and feces; half-life approximately 4.5 hours.

Adverse effects and safety: Typical adverse effects include nausea, diarrhea, and headache. Prolonged therapy can cause thrombocytopenia and peripheral or optic neuropathy. Linezolid is a monoamine oxidase inhibitor, risking hypertensive reactions or serotonin syndrome with certain drugs or high-tyramine foods.

Resistance and notes: Resistance is uncommon but described via 23S rRNA mutations or the cfr gene. Cross-resistance with other protein synthesis inhibitors is limited. Linezolid should be reserved for confirmed or strongly suspected Gram-positive infections when alternatives are unsuitable.