Muscle relaxants: neostigmine after suxamethonium: practice question

A Anaesthesia 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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Anaesthesia · Muscle relaxants: neostigmine after suxamethonium

Sample item

Ten minutes after suxamethonium for intubation, a patient still has depressed twitches without fade on train-of-four. The anaesthetist gives neostigmine hoping to hasten recovery. What is the likely result?

ANo effect because the drug acts at another receptorBPrompt reversal as acetylcholine accumulatesCImmediate return of a full train-of-four ratioDProlongation of the block

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

The answer and the reasoning

D. Prolongation of the block

Suxamethonium is broken down by plasma cholinesterase, which neostigmine also inhibits. Extra acetylcholine at the junction adds to the depolarisation, so the block deepens or lasts longer instead of reversing. Anticholinesterases are for non-depolarising block only.

Option by option

A. No effect because the drug acts at another receptor
Suxamethonium acts at the same nicotinic receptor, and neostigmine also affects its breakdown.
B. Prompt reversal as acetylcholine accumulates
Accumulating acetylcholine helps against competitive blockers but not against a depolariser.
C. Immediate return of a full train-of-four ratio
A full ratio would require removal of the depolariser, which neostigmine delays.
D. Prolongation of the block (correct)
Correct. Neostigmine blocks the enzyme that destroys suxamethonium and adds to the depolarisation.

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.

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, Prolongation of the block. Suxamethonium is broken down by plasma cholinesterase, which neostigmine also inhibits.

Why is "No effect because the drug acts at another receptor" not the answer?

Suxamethonium acts at the same nicotinic receptor, and neostigmine also affects its breakdown.

Why is "Prompt reversal as acetylcholine accumulates" not the answer?

Accumulating acetylcholine helps against competitive blockers but not against a depolariser.

Why is "Immediate return of a full train-of-four ratio" not the answer?

A full ratio would require removal of the depolariser, which neostigmine delays.

What concept does this question test?

It tests Muscle relaxants: neostigmine after suxamethonium in Anaesthesia. Extra acetylcholine at the junction adds to the depolarisation, so the block deepens or lasts longer instead of reversing. Anticholinesterases are for non-depolarising block only.

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 Muscle relaxants: neostigmine after suxamethonium?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia 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.