Which of the following drugs increases gastro–intestinal motility ?
**Core Concept**
The question is testing the student's knowledge of drugs that affect gastrointestinal motility. Gastrointestinal motility refers to the movement of food through the digestive system, and certain medications can either stimulate or inhibit this process.
**Why the Correct Answer is Right**
Metoclopramide is a prokinetic agent that increases gastrointestinal motility by stimulating the motilin receptors in the stomach and small intestine. This leads to enhanced contraction of the upper gastrointestinal tract and accelerated gastric emptying. Metoclopramide also blocks dopamine receptors in the gastrointestinal tract, which further enhances motility. By increasing the frequency and amplitude of contractions, metoclopramide helps to facilitate the movement of food through the digestive system.
**Why Each Wrong Option is Incorrect**
**Option A:** Domperidone is a dopamine antagonist that also increases gastrointestinal motility, but it does so by blocking dopamine receptors in the gastrointestinal tract, rather than stimulating motilin receptors. While it has a similar effect, it is not the correct answer.
**Option B:** Ondansetron is a serotonin 5-HT3 receptor antagonist that is primarily used to prevent nausea and vomiting. It does not increase gastrointestinal motility.
**Option C:** Loperamide is an opioid receptor agonist that slows down gastrointestinal motility, rather than increasing it. It is used to treat diarrhea.
**Clinical Pearl / High-Yield Fact**
Metoclopramide can cause extrapyramidal side effects, such as dystonia and parkinsonism, due to its dopamine receptor antagonism.
**Correct Answer:** C. Loperamide is an opioid receptor agonist that slows down gastrointestinal motility, rather than increasing it. It is used to treat diarrhea.