Linezolid

• MRSA Infections
• Vancomycin-Resistant Enterococcus (VRE)
• Hospital-Acquired Pneumonia
• Complicated Skin Infections

Linezolid is an oxazolidinone antibiotic used to treat serious infections caused by Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). This synthetic antibiotic offers both IV and oral administration with excellent oral bioavailability.

Mechanism of Action

Linezolid exerts its antibacterial effect by inhibiting bacterial protein synthesis through a unique mechanism. It binds to the 23S ribosomal RNA of the 50S subunit at a site close to the interface with the 30S subunit, preventing the formation of a functional 70S initiation complex. This early inhibition of translation is distinct from other protein synthesis inhibitors that act on later steps. Because of this unique mechanism, linezolid does not exhibit cross-resistance with other antimicrobial classes. The drug is bacteriostatic against most organisms, though it may be bactericidal against some streptococci.

Available Formulations

Linezolid is available as tablets (600 mg), oral suspension (100 mg/5 mL), and intravenous solution (2 mg/mL in 100 mL, 200 mL, and 300 mL bags). The tablets and suspension can be taken with or without food. Oral bioavailability is approximately 100%, allowing direct conversion between IV and oral forms.

Medical Uses

Linezolid is FDA-approved for vancomycin-resistant Enterococcus faecium (VRE) infections including bacteremia, nosocomial pneumonia caused by Staphylococcus aureus (including MRSA) or Streptococcus pneumoniae, complicated skin and skin structure infections (including diabetic foot infections), community-acquired pneumonia caused by S. pneumoniae or MRSA, and uncomplicated skin infections. It is often used when vancomycin cannot be used or has failed.

Dosing Guidelines

For most infections, the dose is 600 mg every 12 hours (IV or oral). Duration varies by indication: 10-14 days for VRE, pneumonia, and complicated skin infections; 10-28 days for diabetic foot infections; 10-14 days for uncomplicated skin infections (400 mg every 12 hours may be used). Treatment should continue until infection resolution or up to 28 days maximum due to toxicity risk. No dose adjustment is needed for renal impairment.

Important Safety Information

Myelosuppression (thrombocytopenia, anemia, leukopenia) may occur, particularly with treatment duration exceeding 2 weeks. Complete blood counts should be monitored weekly. Peripheral and optic neuropathy have been reported, sometimes irreversible; the medication should be discontinued if these occur. Serotonin syndrome can occur when combined with serotonergic agents. Linezolid has weak MAO inhibitor activity; patients should avoid large amounts of tyramine-containing foods. Lactic acidosis has been reported.

Drug Interactions

Linezolid has weak, reversible MAO inhibitor activity. Serotonergic drugs (SSRIs, SNRIs, TCAs, meperidine, tramadol, buspirone) should be avoided if possible due to serotonin syndrome risk; if essential, monitor closely. Adrenergic agents (dopamine, epinephrine, pseudoephedrine) may have enhanced pressor effects. Tyramine-rich foods should be limited (though effect is less than with irreversible MAO inhibitors). No significant CYP450 interactions.

Special Populations

There are no adequate studies in pregnant women; use only if clearly needed. Linezolid is excreted in rat milk; use caution during breastfeeding. Safety and efficacy have been established in pediatric patients from birth through 11 years. Elderly patients do not require dose adjustment. No dose adjustment is needed for renal impairment, though metabolites accumulate and their clinical significance is unknown. No dose adjustment is needed for mild to moderate hepatic impairment; safety in severe impairment has not been established.