Cisapride differs from metoclopramide in which of the following aspect?
**Core Concept**
Cisapride and metoclopramide are both prokinetic agents used to enhance gastrointestinal motility, but they have distinct mechanisms of action. Cisapride acts as a selective serotonin 5-HT4 receptor agonist, whereas metoclopramide is a dopamine D2 receptor antagonist with some serotonin 5-HT3 receptor antagonism.
**Why the Correct Answer is Right**
Cisapride's mechanism of action involves the activation of 5-HT4 receptors in the enteric nervous system, leading to increased acetylcholine release and enhanced gut motility. This is in contrast to metoclopramide, which primarily acts by blocking dopamine D2 receptors in the chemoreceptor trigger zone of the brain, thereby reducing vomiting and increasing gut motility through a different pathway.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cisapride does not act by blocking dopamine receptors; that is a characteristic of metoclopramide.
**Option B:** This option is incorrect because metoclopramide also has prokinetic effects, although its mechanism is different from that of cisapride.
**Option C:** This option is incorrect because both cisapride and metoclopramide can cause gastrointestinal side effects, such as diarrhea and abdominal cramps.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that cisapride has been withdrawn from the market in many countries due to its association with severe cardiac arrhythmias, particularly QT interval prolongation. Metoclopramide, on the other hand, has a different side effect profile and is still widely used for prokinetic and antiemetic purposes.
**Correct Answer:** D.