Antimicrobials · Oxazolidinones
The facts most likely to be tested
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Linezolid inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, preventing the formation of the initiation complex.
Linezolid is primarily indicated for the treatment of Vancomycin-resistant Enterococcus (VRE) and Methicillin-resistant Staphylococcus aureus (MRSA) infections.
Linezolid acts as a non-selective monoamine oxidase inhibitor (MAOI), posing a significant risk for serotonin syndrome when combined with serotonergic agents.
Prolonged use of linezolid is associated with bone marrow suppression, specifically thrombocytopenia, requiring regular complete blood count (CBC) monitoring.
Patients on long-term linezolid therapy are at risk for irreversible peripheral neuropathy and optic neuritis.
Linezolid is associated with lactic acidosis, which may present as unexplained nausea, vomiting, or tachypnea.
Linezolid exhibits 100% oral bioavailability, allowing for seamless transition from intravenous to oral therapy.
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A 62-year-old male with a history of chronic wounds is currently hospitalized for a persistent Vancomycin-resistant Enterococcus (VRE) infection. He has been receiving intravenous linezolid for 16 days. Today, the patient reports blurred vision and a sensation of numbness and tingling in his distal extremities. Laboratory studies reveal a platelet count of 78,000/µL, down from 210,000/µL at the start of therapy.
Which of the following adverse effects is most likely responsible for the patient's current neurological symptoms?
Peripheral neuropathy and optic neuritis
The patient is exhibiting classic signs of long-term linezolid toxicity, specifically peripheral neuropathy and optic neuritis, which are well-documented complications of therapy exceeding two weeks.
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High yield triage
Classification
Oxazolidinone class; bacteriostatic protein synthesis inhibitor.
Indications
MRSA and VRE infections, specifically pneumonia and skin/soft tissue infections.
Mechanism of Action
Binds to 50S ribosomal subunit to inhibit bacterial protein synthesis.
Side Effects
Thrombocytopenia, serotonin syndrome, peripheral neuropathy.
Contraindications / Monitoring
MAOI use; monitor CBC weekly for myelosuppression.
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Mechanism of Action
Linezolid binds to the 23S ribosomal RNA of the 50S subunit, preventing the formation of the 70S initiation complex. By inhibiting the early stages of bacterial protein synthesis, it effectively halts bacterial growth. It is primarily bacteriostatic against most organisms, though it exhibits bactericidal activity against Streptococcus pneumoniae.
Unique Properties
It provides excellent tissue penetration, including high concentrations in the lungs and cerebrospinal fluid. Unlike many other anti-MRSA agents, it is available in both oral and intravenous formulations with 100% bioavailability.
Indications
Indicated for vancomycin-resistant Enterococcus (VRE) infections and methicillin-resistant Staphylococcus aureus (MRSA). It is a preferred agent for nosocomial pneumonia and complicated skin and soft tissue infections where vancomycin is ineffective or contraindicated.
Pharmacokinetics
Metabolized via non-enzymatic oxidation; it does not rely on the cytochrome P450 system, minimizing drug-drug interactions. It is primarily excreted by the kidneys, though no dose adjustment is required for renal impairment.
Contraindications
Concurrent use with MAO inhibitors is strictly contraindicated due to the risk of hypertensive crisis. Avoid in patients taking SSRIs or SNRIs unless absolutely necessary, due to the risk of life-threatening serotonin syndrome.
Monitoring
Perform a complete blood count (CBC) weekly to monitor for anemia, leukopenia, and thrombocytopenia. Assess for signs of peripheral neuropathy or optic neuritis during long-term therapy.
Clinical Pearls
Think of Linezolid when the board describes a patient with VRE or MRSA pneumonia who cannot tolerate vancomycin. Always screen for serotonergic medications to avoid the classic serotonin syndrome board trap.