Toxicology: paraquat: 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 · Toxicology: paraquat

Sample item

A 20-year-old man swallowed a herbicide. He has oral mucosal ulceration and then renal failure, and 10 days later progressive breathlessness with hypoxaemia and fibrosis on imaging. Which mechanism explains the lung injury?

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

The answer and the reasoning

A. Redox cycling that generates reactive oxygen species in alveolar type II cells

Paraquat is actively taken up by alveolar type I and II cells and undergoes cyclic reduction and re-oxidation, producing superoxide radicals and depleting NADPH, which causes lipid peroxidation and progressive pulmonary fibrosis. High oxygen concentrations increase the injury, so oxygen is withheld unless hypoxia is severe. There is no specific antidote, and early gut decontamination is vital.

Option by option

  • A. Redox cycling that generates reactive oxygen species in alveolar type II cells (correct)

    Redox cycling generates free radicals that damage pneumocytes and cause fibrosis.

  • B. Binding to haemoglobin to form carboxyhaemoglobin

    Carboxyhaemoglobin forms in carbon monoxide poisoning.

  • C. Release of cyanide in the lung

    Cyanide release is not part of paraquat toxicity.

  • D. Inhibition of acetylcholinesterase in the lung

    Cholinesterase inhibition causes bronchorrhoea and not fibrosis.

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 A, Redox cycling that generates reactive oxygen species in alveolar type II cells. Paraquat is actively taken up by alveolar type I and II cells and undergoes cyclic reduction and re-oxidation, producing superoxide radicals and depleting NADPH, which causes lipid peroxidation and progressive pulmonary fibrosis.

Why is "Binding to haemoglobin to form carboxyhaemoglobin" not the answer?

Carboxyhaemoglobin forms in carbon monoxide poisoning.

Why is "Release of cyanide in the lung" not the answer?

Cyanide release is not part of paraquat toxicity.

Why is "Inhibition of acetylcholinesterase in the lung" not the answer?

Cholinesterase inhibition causes bronchorrhoea and not fibrosis.

What concept does this question test?

It tests Toxicology: paraquat in Pharmacology. High oxygen concentrations increase the injury, so oxygen is withheld unless hypoxia is severe. There is no specific antidote, and early gut decontamination is vital.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Toxicology: paraquat?

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.