Antibacterials: linezolid prolonged therapy: practice question

A Pharmacology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pharmacology · Antibacterials: linezolid prolonged therapy

Sample item

A 30-year-old man with drug-resistant tuberculosis has been on a linezolid-containing regimen for six weeks. His platelet count has fallen to 60 x 10^9/L and haemoglobin has dropped. Which statement best describes this toxicity?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Reversible myelosuppression related to duration of therapy, from inhibition of mitochondrial protein synthesis

Linezolid binds the 50S ribosomal subunit and also inhibits mitochondrial protein synthesis. With courses longer than about two weeks it causes myelosuppression (especially thrombocytopenia and anaemia), and also peripheral and optic neuropathy and lactic acidosis. Blood counts are monitored and the effect usually reverses on dose reduction or stopping.

Option by option

  • A. Immune-mediated platelet destruction that begins within days of the first dose

    Heparin-type immune thrombocytopenia occurs early after exposure, which does not fit a six-week course with falling haemoglobin.

  • B. Direct bone marrow infiltration by mycobacteria

    Marrow infiltration would not explain the temporal relation to linezolid.

  • C. Reversible myelosuppression related to duration of therapy, from inhibition of mitochondrial protein synthesis (correct)

    Correct. Duration-dependent, reversible marrow suppression is the classic linezolid toxicity.

  • D. Haemolysis from G6PD deficiency

    Haemolysis is not the usual mechanism and linezolid is not a typical oxidant haemolytic drug.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is C, Reversible myelosuppression related to duration of therapy, from inhibition of mitochondrial protein synthesis. Linezolid binds the 50S ribosomal subunit and also inhibits mitochondrial protein synthesis.

Why is "Immune-mediated platelet destruction that begins within days of the f…" not the answer?

Heparin-type immune thrombocytopenia occurs early after exposure, which does not fit a six-week course with falling haemoglobin.

Why is "Direct bone marrow infiltration by mycobacteria" not the answer?

Marrow infiltration would not explain the temporal relation to linezolid.

Why is "Haemolysis from G6PD deficiency" not the answer?

Haemolysis is not the usual mechanism and linezolid is not a typical oxidant haemolytic drug.

What concept does this question test?

It tests Antibacterials: linezolid prolonged therapy in Pharmacology. With courses longer than about two weeks it causes myelosuppression (especially thrombocytopenia and anaemia), and also peripheral and optic neuropathy and lactic acidosis. Blood counts are monitored and the effect usually reverses on dose reduction or stopping.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Antibacterials: linezolid prolonged therapy?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.