Which one of the following drugs increases gastrointestinal motility –
First, I remember that drugs affecting GI motility can be either prokinetic or antispasmodic. Prokinetic drugs increase motility, while antispasmodics decrease it. Common prokinetic agents include metoclopramide, domperidone, and erythromycin. Metoclopramide is a dopamine receptor antagonist that acts on the upper GI tract, enhancing peristalsis. Domperidone is similar but has less central nervous system effects. Erythromycin, an antibiotic, also acts as a prokinetic agent by stimulating motilin receptors.
Now, looking at the options (even though they're not listed), I need to consider typical distractors. Common incorrect options might be anticholinergics like atropine, which decrease motility. Opioids like morphine also slow GI motility. Antispasmodics such as hyoscine (Buscopan) are used for cramps but don't increase motility. Antacids or H2 blockers (e.g., ranitidine) reduce acid but don't affect motility.
The core concept here is understanding the mechanism of prokinetic drugs versus those that decrease motility. The correct answer would be a drug that enhances peristalsis, like metoclopramide. The other options are incorrect because they either block motility or have different primary actions.
For the clinical pearl, remembering that metoclopramide is a first-line prokinetic agent with dopamine antagonist action is key. Also, erythromycin's role as a prokinetic might be a less common but important fact for exams.
I need to structure the explanation with the required sections, ensuring each part is concise and covers the necessary points. The correct answer line should be at the end with the letter and answer text.
**Core Concept**
Gastrointestinal motility is regulated by neurotransmitters like acetylcholine and dopamine. Prokinetic drugs enhance peristalsis by stimulating cholinergic pathways or modulating dopamine receptors, while anticholinergics/antispasmodics reduce motility.
**Why the Correct Answer is Right**
Metoclopramide is a dopamine D2 receptor antagonist that increases acetylcholine release in the GI tract, enhancing gastric emptying and intestinal motility. It acts on the upper GI tract and is used for conditions like gastroparesis or GERD. Its prokinetic effect is mediated via central and peripheral dopaminergic blockade.
**Why Each Wrong Option is Incorrect**
**Option A:** Atropine is an anticholinergic that inhibits acetylcholine action, decreasing GI motility.
**Option B:** Ondansetron is a 5-HT3 antagonist used for nausea/vomiting but does not affect motility.
**Option C:** Loperamide is an opioid receptor agonist that slows GI transit by reducing peristalsis.
**Clinical Pearl / High-Yield Fact**
Remember "Metoclopramide = Motility + Dopamine block" for prokinetic action. Avoid using anticholinergics