Linezolid

Linezolid

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linezolid mechanism of action spectrum indications

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linezolid adverse effects toxicity dosing pharmacokinetics

GradeResponse

Drug Class

Oxazolidinone antibiotic — the first synthetic antibacterial class introduced in decades.

Mechanism of Action

Linezolid inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, preventing formation of the 70S initiation complex (fusion of the 30S and 50S subunits). This is a unique binding site distinct from other ribosomal antibiotics, explaining the lack of cross-resistance.

Its toxicity in humans arises from the same mechanism: it also binds human mitochondrial ribosomes, inhibiting mitochondrial protein synthesis.

Spectrum of Activity

Organism Group	Activity
MRSA, VRSA	✅ Excellent
VRE (E. faecium, E. faecalis)	✅ Excellent
Streptococci (including penicillin-resistant)	✅ Excellent
Clostridioides difficile	✅ Active
Mycobacterium tuberculosis (MDR/XDR)	✅ Active (off-label)
Non-tuberculous mycobacteria (NTM)	✅ In vitro activity
Gram-negative organisms	❌ Poor/inactive

Pharmacokinetics

Oral bioavailability: ~100% (IV and oral doses are interchangeable)
Distribution: excellent tissue and fluid penetration, including CSF
Half-life: ~5–7 hours
Metabolism: hepatic oxidation (non-CYP mediated)
No dose adjustment required for renal impairment

Clinical Indications

MRSA infections — skin/soft tissue, pneumonia (nosocomial/VAP), bacteremia
VRE infections — particularly E. faecium
Drug-resistant TB (MDR-TB/XDR-TB) — key component of WHO Group B regimens; 600 mg/day preferred (equivalent efficacy, fewer adverse events vs. 1,200 mg/day)
Penicillin-resistant pneumococcal pneumonia
Diabetic foot infections (as part of combination therapy)

Dosing

Indication	Dose	Route	Duration
Gram-positive infections (adults)	600 mg every 12 h	IV or PO	10–28 days
MDR-TB (adults)	600 mg once daily	PO	6–24 months
Pediatric	10 mg/kg every 8–12 h	IV or PO	Per indication

Adverse Effects

Common / Dose-dependent:

Myelosuppression (thrombocytopenia > anemia > neutropenia) — most common serious toxicity; monitor CBC weekly
Peripheral neuropathy — usually with prolonged use (>4 weeks)
Optic neuropathy — can cause irreversible vision loss with long-term use
Lactic acidosis — due to mitochondrial toxicity; rare but life-threatening
GI upset (nausea, diarrhea, vomiting)

Pharmacodynamic interactions:

Linezolid is a weak MAO inhibitor (MAOI) — risk of serotonin syndrome when combined with:
- SSRIs, SNRIs, TCAs, meperidine, tramadol, dextromethorphan
- Sympathomimetic/adrenergic agents → hypertensive crisis risk
Tyramine-containing foods (aged cheese, cured meats, wine) should be limited

Resistance

Clinical resistance is typically associated with:

Mutations in 23S rRNA (most common)
Mutations in ribosomal proteins L3 (rplC) and L4 (rplD)
cfr gene (methyltransferase) — transferable; modifies 23S rRNA

Monitoring

CBC with differential weekly (especially platelets)
Visual acuity and color vision for courses >4 weeks
Lactate if symptoms of lactic acidosis arise
Therapeutic drug monitoring (TDM) recommended for prolonged MDR-TB courses to reduce toxicity (Treatment of Drug-Resistant Tuberculosis, p. 24)
Avoid or minimize use beyond 28 days for standard infections where alternatives exist

Key Clinical Pearls

One of the few oral options for MRSA pneumonia with excellent lung penetration
Unlike vancomycin, no renal dose adjustment is needed
For MDR-TB: the 600 mg once-daily dose has equivalent efficacy and substantially fewer adverse events (46.7% vs. 74.5%) compared to 1,200 mg/day (Treatment of Drug-Resistant Tuberculosis, p. 24)
Bacteriostatic against most organisms (bactericidal against streptococci)
Can be used in patients with renal failure or on dialysis without dose modification

(Harrison's Principles of Internal Medicine, 21st ed., p. 5280; Treatment of Drug-Resistant Tuberculosis, p. 24)

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