Muscle relaxants: pseudocholinesterase deficiency: 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: pseudocholinesterase deficiency

Sample item

A patient remains apnoeic for 3 hours after suxamethonium. The dibucaine number is 20. What is the genotype?

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

The answer and the reasoning

C. Homozygous atypical gene

Dibucaine inhibits normal cholinesterase by about 80% and atypical enzyme by about 20%. A dibucaine number of 70 to 80 is normal, 40 to 60 heterozygous and under 30 homozygous atypical, causing blocks lasting 4 to 8 hours.

Option by option

  • A. Normal homozygous

    Normal homozygotes have about 80.

  • B. Fluoride-resistant variant carrier only

    Fluoride number tests a different variant.

  • C. Homozygous atypical gene (correct)

    Correct. A dibucaine number around 20 is homozygous atypical.

  • D. Heterozygous atypical gene

    Heterozygotes have values of about 40 to 60.

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 Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is C, Homozygous atypical gene. Dibucaine inhibits normal cholinesterase by about 80% and atypical enzyme by about 20%.

Why is "Normal homozygous" not the answer?

Normal homozygotes have about 80.

Why is "Fluoride-resistant variant carrier only" not the answer?

Fluoride number tests a different variant.

Why is "Heterozygous atypical gene" not the answer?

Heterozygotes have values of about 40 to 60.

What concept does this question test?

It tests Muscle relaxants: pseudocholinesterase deficiency in Anaesthesia. A dibucaine number of 70 to 80 is normal, 40 to 60 heterozygous and under 30 homozygous atypical, causing blocks lasting 4 to 8 hours.

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: pseudocholinesterase deficiency?

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.