Mechanism of Action
Linezolid (Linezolid) is a synthetic antibacterial agent and a member of the oxazolidinone class. Its mechanism of action involves the inhibition of bacterial protein synthesis. The drug selectively binds to the 50S ribosomal subunit of the bacterial cell, preventing the formation of the functional initiation complex required for translation.
In terms of its binding site (acting on the 50S subunit), linezolid shares similarities with macrolides, ketolides, lincosamides, and chloramphenicol, but it differs in chemical structure and exhibits no cross-resistance with them.
Spectrum of Activity
The drug has a narrow yet clinically vital spectrum of activity, targeting primarily Gram-positive flora. Its key feature is high activity against multidrug-resistant ("problematic") pathogens that standard beta-lactams cannot handle.
Susceptible flora include:
- Staphylococcus aureus, including MRSA (methicillin-resistant Staphylococcus aureus). Linezolid is active against both nosocomial (hospital-acquired) and community-acquired strains resistant to oxacillin and methicillin.
- Penicillin-resistant strains of Streptococcus and Pneumococcus.
- VRE (vancomycin-resistant enterococci and staphylococci).
Indications
Linezolid is a drug of choice (along with the glycopeptide vancomycin) for the treatment of severe infections caused by MRSA.
Furthermore, it is completely indispensable for infectious processes associated with vancomycin-resistant strains (VRE). In situations where glycopeptide drugs (vancomycin, teicoplanin) prove ineffective due to pathogen mutations, linezolid remains one of the few available lines of defense.
Adverse Effects and Drug Interactions
A crucial pharmacological feature of linezolid that is frequently overlooked is its ability to act as a non-selective, reversible monoamine oxidase (MAO) inhibitor. This creates severe risks of dangerous drug interactions.
- When co-administered with drugs affecting monoamine and serotonin reuptake (e.g., antidepressants), the risk of severe neurological and cardiovascular complications increases critically.
- Possible reactions include severe headache, tachycardia (rapid heart rate), and a sharp rise in blood pressure (hypertensive crisis).
- The most formidable, life-threatening condition associated with this interaction is serotonin syndrome.
Dosage Forms and Administration
The drug is available in formulations for parenteral and oral administration, which is convenient for step-down therapy:
- Tablets: 600 mg. Administered orally at a dose of 0.8–1.2 g/day, divided into 2 doses.
- Infusion solution: 0.2% bags (300 mL). Administered intravenously via drip over 30–120 minutes.