Generic Name

Linezolid

Mechanism

• Inhibition of bacterial protein synthesis by binding to the 50S ribosomal subunit, preventing the formation of the 70S initiation complex.
• Unique among oxazolidinones: induces a reversible inhibition of peptidyl transferase activity, leading to blockade of the 70S complex without ribosomal dissociation.
• Activity is broad‑spectrum gram‑positive, including MRSA, VRE, and *C. difficile* isolates resistant to linezolid‑sensitive strains.

Pharmacokinetics

• Oral bioavailability ≈ 100 %; parenteral form (IV) achieves comparable serum levels.
• *Distribution*: Widely distributes into tissues, including lung, skin, and CSF; protein binding ~30 %.
• Metabolism: minimal (≈ 20 % conjugated, 30 % aromatic oxidation); no major hepatic CYP interactions.
• Elimination: Primarily renal excretion (~50 % unchanged).
• Half‑life: 5.5–6 h; steady state reached in 24 h.
• Renal adjustment: reduce dose by 50 % in CrCl 30‑50 mL/min; no dose adjustment if CrCl >50 mL/min.

Indications

• Complicated skin and skin-structure infections (cSSSI), community‑acquired MRSA infections, and VRE bacteremia.
• Hospital‑acquired and ventilator‑associated pneumonia caused by gram‑positive organisms when β‑lactam options are limited.
• Clostridioides difficile (formerly *C. difficile*) confirmed in hospitalized patients when first‑line metronidazole or vancomycin fails.

Contraindications

• Severe hepatic impairment (Child‑Pugh C): avoid; monitor LFTs closely.
• Serotonin syndrome: contraindicated when co‑administered with SSRIs, SNRIs, TCAs, tramadol, fentanyl, or MAO inhibitors.
• Myelosuppressive conditions: cirrhosis, pre‑existing cytopenias—monitor CBC every 3–5 days.
• Pregnancy: Category C; avoid unless benefit outweighs risk.
• New‑borns / infants: not indicated; pharmacokinetics and safety profile unstudied.

Dosing

• Duration: 7–14 days for cSSSI; 14–28 days for bacteremia/VRE; ≤ 12 days for CDI if cured.
• Loading dose not required; steady state achieved quickly.

Adverse Effects

• Common
• Nausea, vomiting, diarrhea
• Anemia, thrombocytopenia
• Mild headache, dizziness
• Serious
• Peripheral neuropathy & optic neuropathy after prolonged use (>2 weeks).
• Serotonin syndrome (irritability, hyperthermia, seizures).
• Severe myelosuppression (aplastic anemia, neutropenia).
• QT prolongation (rare; monitor ECG in high‑risk patients).
• Drug–drug interactions: MAOIs, SSRIs, SNRIs, tramadol, fentanyl.

Monitoring

• CBC (neutrophils, platelets, hemoglobin) every 3–5 days while on therapy.
• LFTs (ALT/AST) baseline and every 2–3 weeks.
• Renal function (CrCl) baseline and every 2–3 weeks.
• Neurologic assessment: vision check at 2 weeks if prolonged use, and for signs of neuropathy.
• Serotonin level symptoms: check if any serotonergic agent is co‑administered.

Clinical Pearls

• Great for MRSA & VRE: Its unique mechanism gives activity against organisms that are resistant to glycopeptides, linezolid‑resistant Gram‑positives notwithstanding.
• Avoid pairing with SSRIs/SNRIs: Even a single dose of Linezolid can precipitate serotonin syndrome‐compatible symptoms.
• Rapid microbiologic suppression: In vitro susceptibility patterns demonstrate 25‑hour inhibition, making it a good bridge while awaiting culture results.
• Procalcitonin drop: Monitor serum procalcitonin resolution; a >70 % drop after 48 h predicts response.
• Non‑renal clearance component: Because of minimal metabolism, Linezolid can be safely used to avoid drug‑drug interactions with hepatic CYP‑dependent antibiotics.
• Caution in elderly: Increased incidence of neuropathy—limit duration to ≤ 2 weeks when possible, especially in patients >75 years.
• Reducing dosage for renal impairment, not by splitting tablets but by adjusting the total daily dose (e.g., 300 mg q12 h).

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• *This drug card provides concise, evidence‑based guidance and is optimized for quick reference by medical students and clinicians.*