Pregnancy: magnesium sulphate 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 · Pregnancy: magnesium sulphate toxicity

Sample item

A woman with severe pre-eclampsia on a magnesium sulphate infusion becomes drowsy. Her patellar reflexes are absent and her respiratory rate is 8 per minute. What is the immediate step?

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

The answer and the reasoning

D. Stop the infusion and give intravenous calcium gluconate

Magnesium toxicity first shows as loss of the patellar reflex, followed by respiratory depression and cardiac arrest at higher levels. The infusion is stopped and 10% calcium gluconate is given intravenously as the antidote, with ventilatory support as needed. Reflexes, respiratory rate and urine output are monitored routinely during therapy.

Option by option

  • A. Reduce the infusion by half and give naloxone

    Naloxone is an opioid antidote and does not reverse magnesium toxicity.

  • B. Give intravenous flumazenil

    Flumazenil reverses benzodiazepines and has no effect on magnesium.

  • C. Give intravenous neostigmine

    Neostigmine does not reliably reverse magnesium-induced weakness and may cause bradycardia.

  • D. Stop the infusion and give intravenous calcium gluconate (correct)

    Correct. Calcium antagonises magnesium at the neuromuscular junction and in the heart.

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 D, Stop the infusion and give intravenous calcium gluconate. Magnesium toxicity first shows as loss of the patellar reflex, followed by respiratory depression and cardiac arrest at higher levels.

Why is "Reduce the infusion by half and give naloxone" not the answer?

Naloxone is an opioid antidote and does not reverse magnesium toxicity.

Why is "Give intravenous flumazenil" not the answer?

Flumazenil reverses benzodiazepines and has no effect on magnesium.

Why is "Give intravenous neostigmine" not the answer?

Neostigmine does not reliably reverse magnesium-induced weakness and may cause bradycardia.

What concept does this question test?

It tests Pregnancy: magnesium sulphate toxicity in Pharmacology. The infusion is stopped and 10% calcium gluconate is given intravenously as the antidote, with ventilatory support as needed. Reflexes, respiratory rate and urine output are monitored routinely during therapy.

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 Pregnancy: magnesium sulphate 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.