Antibiotics: macrolides as prokinetics: 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 · Antibiotics: macrolides as prokinetics

Sample item

A 50-year-old diabetic with symptomatic gastroparesis does not respond to dietary change. Low-dose erythromycin is added. By which mechanism does it improve gastric emptying?

AAntagonism at dopamine D2 receptorsBAgonism at 5-HT4 receptorsCAgonism at motilin receptorsDInhibition of acetylcholinesterase

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

The answer and the reasoning

C. Agonism at motilin receptors

Erythromycin mimics motilin, a gut hormone that triggers migrating motor complexes, by acting on motilin receptors in the stomach and duodenum. This is why diarrhoea and cramps are common with macrolides and why it is used short term as a prokinetic. Tachyphylaxis develops with prolonged use.

Option by option

A. Antagonism at dopamine D2 receptors
D2 antagonism is the mechanism of metoclopramide and domperidone.
B. Agonism at 5-HT4 receptors
5-HT4 agonism is the mechanism of prucalopride and cisapride, not erythromycin.
C. Agonism at motilin receptors (correct)
Correct. Motilin receptor stimulation produces strong antral contractions.
D. Inhibition of acetylcholinesterase
Acetylcholinesterase inhibition is the mechanism of neostigmine and not of erythromycin.

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 Pharmacology question

What is the answer to this Pharmacology question?

The best answer is C, Agonism at motilin receptors. Erythromycin mimics motilin, a gut hormone that triggers migrating motor complexes, by acting on motilin receptors in the stomach and duodenum.

Why is "Antagonism at dopamine D2 receptors" not the answer?

D2 antagonism is the mechanism of metoclopramide and domperidone.

Why is "Agonism at 5-HT4 receptors" not the answer?

5-HT4 agonism is the mechanism of prucalopride and cisapride, not erythromycin.

Why is "Inhibition of acetylcholinesterase" not the answer?

Acetylcholinesterase inhibition is the mechanism of neostigmine and not of erythromycin.

What concept does this question test?

It tests Antibiotics: macrolides as prokinetics in Pharmacology. This is why diarrhoea and cramps are common with macrolides and why it is used short term as a prokinetic. Tachyphylaxis develops with prolonged use.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Antibiotics: macrolides as prokinetics?

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.