Cardiovascular drugs: nitroprusside toxicity: 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 · Cardiovascular drugs: nitroprusside toxicity

Sample item

A 48-year-old woman with renal impairment has been on a sodium nitroprusside infusion at a high rate for 3 days for hypertensive emergency. She now has confusion, severe lactic acidosis and a raised venous oxygen saturation. Which drug should be given?

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

The answer and the reasoning

D. Sodium thiosulfate

Nitroprusside releases nitric oxide and five cyanide ions per molecule. Cyanide is normally converted to thiocyanate by rhodanese, but high doses or renal impairment lead to accumulation, histotoxic hypoxia and lactic acidosis, with high venous oxygen saturation as tissues cannot use oxygen. Sodium thiosulfate supplies sulfur for rhodanese, and hydroxocobalamin is also used.

Option by option

  • A. Dimercaprol

    Dimercaprol is a chelator for arsenic, mercury and gold.

  • B. Pralidoxime

    Pralidoxime reactivates cholinesterase in organophosphate poisoning.

  • C. Methylene blue

    Methylene blue treats methaemoglobinaemia and does not detoxify cyanide.

  • D. Sodium thiosulfate (correct)

    Correct. Thiosulfate promotes conversion of cyanide to harmless thiocyanate.

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.

More Pharmacology questions

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is D, Sodium thiosulfate. Nitroprusside releases nitric oxide and five cyanide ions per molecule.

Why is "Dimercaprol" not the answer?

Dimercaprol is a chelator for arsenic, mercury and gold.

Why is "Pralidoxime" not the answer?

Pralidoxime reactivates cholinesterase in organophosphate poisoning.

Why is "Methylene blue" not the answer?

Methylene blue treats methaemoglobinaemia and does not detoxify cyanide.

What concept does this question test?

It tests Cardiovascular drugs: nitroprusside toxicity in Pharmacology. Cyanide is normally converted to thiocyanate by rhodanese, but high doses or renal impairment lead to accumulation, histotoxic hypoxia and lactic acidosis, with high venous oxygen saturation as tissues cannot use oxygen. Sodium thiosulfate supplies sulfur for rhodanese, and hydroxocobalamin is also used.

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 Cardiovascular drugs: nitroprusside toxicity?

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.