Drugs for Gastrointestinal Diseases Practice Questions

Q: Which of the following drugs commonly causes diarrhea as a side effect?

Magnesium sulfate. **Explanation:** **Magnesium sulfate** is the correct answer because it acts as an **osmotic laxative**. Magnesium salts are poorly absorbed in the gastrointestinal tract. Their presence in the intestinal lumen creates an osmotic gradient that draws water into the bowel, increasing intraluminal pressure and stimulating peristalsis. This mechanism is why magnesium-containing antacids and laxatives commonly cause **diarrhea** as a side effect. **Analysis of Incorrect Options:** * **Morphine:** As an opioid agonist, it acts on $\mu$-receptors in the myenteric plexus to decrease intestinal motility and increase sphincter tone. This leads to **constipation**, not diarrhea. * **Atropine:** This is a muscarinic antagonist (anticholinergic). By blocking parasympathetic stimulation of the gut, it reduces secretions and slows down GI motility, leading to **constipation** and dry mouth. * **Lithium:** While lithium can occasionally cause acute nausea or diarrhea during the initiation of therapy, its classic and most high-yield GI-related side effect in chronic use is not diarrhea, but rather its interference with ADH (causing nephrogenic diabetes insipidus). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Antacids:** **M**agnesium **M**akes stool **M**ove (Diarrhea); **A**luminum **A**lways **A**rrests stool (Constipation). * **Therapeutic Use:** Magnesium sulfate is the drug of choice for **Eclampsia** (seizures) and is also used in Torsades de Pointes. * **Contraindication:** Magnesium salts should be avoided in patients with **renal failure** due to the risk of hypermagnesemia (causing muscle weakness and respiratory depression).

Q: Aprepitant is used as:

Antiemetic. **Explanation:** **Aprepitant** is a selective, high-affinity antagonist at the **Substance P/Neurokinin-1 (NK1) receptors** located in the brainstem (area postrema and nucleus tractus solitarius). By blocking these receptors, it inhibits the emetic reflex triggered by Substance P. It is primarily used as an **antiemetic**, specifically for the prevention of both acute and delayed phases of **Chemotherapy-Induced Nausea and Vomiting (CINV)**, often in combination with 5-HT3 antagonists (like Ondansetron) and Dexamethasone. **Analysis of Incorrect Options:** * **A. Antidepressant:** While Substance P is involved in mood regulation, NK1 antagonists have not shown significant efficacy in treating clinical depression. Standard antidepressants include SSRIs, SNRIs, or TCAs. * **C. Antihypertensive:** Aprepitant has no effect on peripheral vascular resistance or cardiac output and is not used to lower blood pressure. * **D. Diuretic:** It does not influence renal electrolyte handling or water excretion. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** NK1 receptor antagonist (blocks Substance P). * **Fosaprepitant:** This is the water-soluble **prodrug** of Aprepitant, administered intravenously. * **Drug Interactions:** Aprepitant is a substrate, moderate inhibitor, and inducer of **CYP3A4**. It can increase levels of drugs like Dexamethasone (dose reduction required) and decrease the efficacy of Warfarin and oral contraceptives. * **Clinical Use:** It is the drug of choice for **delayed emesis** associated with highly emetogenic chemotherapy (e.g., Cisplatin).

Q: All of the following statements are true regarding ondansetron except?

It has significant drug interactions.. ### Explanation **Ondansetron** is a prototype 5-HT3 receptor antagonist widely used in clinical practice. **Why Option C is the correct answer (The False Statement):** Ondansetron is known for its **excellent safety profile** and **minimal drug-drug interactions**. It is metabolized by the hepatic cytochrome P450 system (CYP3A4, CYP2D6, and CYP1A2), but it does not significantly inhibit or induce these enzymes. Unlike many other drugs used in oncology or GI medicine, it rarely requires dose adjustments when co-administered with other medications, making it a preferred choice in multi-drug regimens. **Analysis of Incorrect Options:** * **Option A:** It remains the **first-line drug (DOC)** for preventing and treating chemotherapy-induced nausea and vomiting (CINV), as well as radiotherapy-induced and postoperative vomiting. * **Option B:** Its primary mechanism is the **competitive blockade of 5-HT3 receptors** located both peripherally (on vagal afferents in the GI tract) and centrally (in the Chemoreceptor Trigger Zone/CTZ). * **Option D:** While primarily a 5-HT3 antagonist, some studies suggest ondansetron may possess weak **5-HT4 agonism**, which might contribute to its effects on GI motility, though this is not its main clinical mechanism. **High-Yield NEET-PG Pearls:** * **Side Effects:** The most common side effects are **headache** and **constipation**. * **ECG Changes:** A critical high-yield fact is that ondansetron can cause **QT interval prolongation**; caution is required in patients with electrolyte imbalances or congenital long QT syndrome. * **Site of Action:** It acts at both the **CTZ** (Central) and the **STN/Vagal nerve endings** (Peripheral). * **Ineffectiveness:** It is **not effective** in Motion Sickness (where H1 and M1 blockers are used).

Q: Why is glucose added to oral rehydration solution (ORS)?

To enhance the absorption of sodium and water.. **Explanation:** The addition of glucose to Oral Rehydration Solution (ORS) is based on the physiological principle of **Sodium-Glucose Cotransport**. In the luminal membrane of the small intestine, the **SGLT-1 (Sodium-Glucose Linked Transporter)** protein facilitates the coupled transport of one molecule of glucose with two ions of sodium. As sodium is actively transported into the enterocytes, it creates an osmotic gradient that pulls water along with it (solvent drag). Crucially, this transport mechanism remains intact even during secretory diarrheas like Cholera. Therefore, glucose is not added as a nutrient, but as a functional vehicle to drive the absorption of salt and water. **Analysis of Options:** * **Option B (Correct):** Glucose is the essential substrate required to activate the SGLT-1 transporter, ensuring rehydration. * **Options A & D (Incorrect):** While glucose may slightly improve the taste, this is a secondary benefit. In fact, excessive glucose (hyperosmolar ORS) can worsen diarrhea by causing osmotic water loss into the gut lumen. * **Option C (Incorrect):** Glucose does not act as a preservative; it can actually promote bacterial growth if the solution is contaminated. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Reduced Osmolarity ORS:** The current standard has a total osmolarity of **245 mOsm/L** (Sodium: 75 mmol/L, Glucose: 75 mmol/L). This reduces the need for IV fluids and decreases stool output compared to the older 311 mOsm/L formula. * **Trisodium Citrate:** Added to ORS to correct metabolic acidosis and increase the shelf life (replacing Sodium Bicarbonate). * **Zinc Supplementation:** Recommended alongside ORS (20 mg/day for 14 days) to reduce the duration and severity of diarrhea.

Q: What is the drug of choice for cisplatin-induced emesis?

Ondansetron. **Explanation:** **Correct Answer: C. Ondansetron** Cisplatin is a highly emetogenic chemotherapy agent. It causes nausea and vomiting by damaging enterochromaffin cells in the gastrointestinal tract, leading to a massive release of **serotonin (5-HT)**. This serotonin stimulates **5-HT₃ receptors** on vagal afferents and in the Chemoreceptor Trigger Zone (CTZ). **Ondansetron**, a selective 5-HT₃ receptor antagonist, effectively blocks these receptors, making it the first-line drug of choice for preventing acute chemotherapy-induced nausea and vomiting (CINV). **Analysis of Incorrect Options:** * **A. Metoclopramide:** A D₂ receptor antagonist with prokinetic properties. While used for mild emesis or gastroparesis, it is less effective than 5-HT₃ antagonists for highly emetogenic drugs like cisplatin and carries a risk of extrapyramidal side effects. * **B. Domperidone:** A peripheral D₂ antagonist. It is primarily used for drug-induced nausea (e.g., Levodopa) or GERD but is ineffective against the potent serotonin surge caused by cisplatin. * **C. Octreotide:** A somatostatin analogue used for secretory diarrhea (carcinoid syndrome) or variceal bleeding; it has no role in managing CINV. **NEET-PG High-Yield Pearls:** * **Combination Therapy:** For highly emetogenic chemotherapy (HEC), the current gold standard is a "Triple Regimen": **5-HT₃ Antagonist + Dexamethasone + NK₁ Receptor Antagonist** (e.g., Aprepitant). * **Side Effects:** The most common side effects of Ondansetron are **headache**, constipation, and **QT interval prolongation**. * **Delayed Emesis:** While Ondansetron is excellent for *acute* emesis (first 24 hours), **Aprepitant** is superior for *delayed* emesis (after 24 hours).

Q: Which of the following is NOT an effect of ranitidine when compared to cimetidine?

Anti-androgenic action. **Explanation:** The question asks to identify which effect is **not** associated with ranitidine when compared to cimetidine. Both drugs are H2-receptor antagonists (H2RAs), but they differ significantly in their side-effect profiles and potency. **1. Why "Anti-androgenic action" is the correct answer:** Cimetidine is notorious for its **anti-androgenic effects**. It binds to androgen receptors and inhibits the metabolism of estradiol, leading to clinical conditions such as **gynecomastia** in men and galactorrhea in women. **Ranitidine**, along with newer H2RAs like famotidine, lacks these anti-androgenic properties. Therefore, ranitidine does not cause these hormonal side effects. **2. Analysis of Incorrect Options:** * **A. Action on H2 receptors:** Both drugs share the same primary mechanism of action—competitive inhibition of histamine at H2 receptors on gastric parietal cells to reduce acid secretion. * **B. Given orally:** Both cimetidine and ranitidine have good oral bioavailability and are commonly administered via the oral route. * **C. Used with proton pump inhibitors:** While not a standard first-line combination (as PPIs are superior), both can theoretically be used in specific refractory cases or "nocturnal acid breakthrough" scenarios, though this is a shared clinical context rather than a differentiating side effect. **High-Yield Clinical Pearls for NEET-PG:** * **Enzyme Inhibition:** Cimetidine is a potent **P450 enzyme inhibitor**, leading to numerous drug interactions (e.g., increasing levels of warfarin, phenytoin, and theophylline). Ranitidine has negligible effects on hepatic enzymes. * **Potency:** Ranitidine is 5–10 times more potent than cimetidine. * **Blood-Brain Barrier:** Cimetidine can cross the BBB, occasionally causing confusion or hallucinations in elderly patients; ranitidine has much lower CNS penetration.

Q: What is true about the proton-pump inhibitor omeprazole?

CYP2C19 predicts efficacy.. **Explanation:**1. Why Option B is Correct:Omeprazole is primarily metabolized in the liver by the cytochrome P450 enzyme **CYP2C19**. Genetic polymorphisms in this enzyme significantly influence the drug's pharmacokinetics. Patients who are "poor metabolizers" (common in Asian populations) have higher plasma concentrations and better acid suppression, whereas "rapid metabolizers" may experience therapeutic failure. Therefore, the CYP2C19 genotype is a major predictor of the drug's clinical efficacy and duration of action [3].2. Why Other Options are Incorrect:* **Option A:** Omeprazole is **highly protein-bound** (approximately 95%), mainly to albumin. This is a common characteristic of most proton pump inhibitors (PPIs).* **Option C:** The oral bioavailability of omeprazole is relatively low, around **35–40%** [1], due to its instability in gastric acid (requiring enteric coating) [2] and significant first-pass metabolism. In contrast, drugs like Lansoprazole or Pantoprazole have higher bioavailability (80% or more).* **Option D:** Since A and C are incorrect, "All of the above" is false.**High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Irreversible inhibition of the **H+/K+ ATPase pump** (the "final common pathway" of acid secretion) [2].* **Activation:** Omeprazole is a **prodrug** that requires an acidic environment (pH < 2) in the canaliculi of parietal cells to be converted into its active form (sulfenamide) [1, 2].* **Administration:** Should be taken **30–60 minutes before a meal** (usually breakfast) to ensure peak plasma levels coincide with the maximal activation of proton pumps.* **Drug Interaction:** Omeprazole inhibits CYP2C19, which can **decrease the activation of Clopidogrel** (a prodrug), potentially increasing the risk of cardiovascular events. Pantoprazole is the preferred PPI when using Clopidogrel.

Q: What is the drug of choice for intractable hiccups?

Chlorpromazine. **Chlorpromazine** is the only FDA-approved medication specifically indicated for the treatment of intractable hiccups (singultus). Intractable hiccups are defined as those lasting more than one month. **Why Chlorpromazine is the Correct Choice:** The pathophysiology of hiccups involves a reflex arc consisting of the vagus nerve, phrenic nerve, and sympathetic chain (T6–T12), coordinated by a "hiccup center" in the brainstem. Chlorpromazine, a typical antipsychotic of the low-potency phenothiazine class, acts as a potent **dopamine (D2) receptor antagonist** in the hypothalamus and brainstem. It effectively interrupts the hiccup reflex arc through its central sedative and antagonistic effects. **Analysis of Incorrect Options:** * **Metoclopramide (A):** While it is a prokinetic and D2 antagonist used as a second-line agent (especially if the cause is gastric stasis), it is not the primary drug of choice. * **Haloperidol (B):** This is a high-potency antipsychotic that has been used off-label for hiccups, but it lacks the formal approval and historical clinical preference established for Chlorpromazine. * **Thioridazine (C):** Although it is a phenothiazine like chlorpromazine, it is not used for hiccups due to its significant side-effect profile, including the risk of QTc prolongation. **High-Yield Clinical Pearls for NEET-PG:** * **First-line for Intractable Hiccups:** Chlorpromazine (Oral or IV). * **Alternative/Second-line agents:** Baclofen (GABA-B agonist), Gabapentin, or Metoclopramide. * **Non-pharmacological trigger:** Gastric distension is the most common trigger for acute hiccups. * **Side effect to watch:** When using Chlorpromazine, monitor for hypotension and extrapyramidal symptoms (EPS).

Question 1

Which of the following drugs commonly causes diarrhea as a side effect?

Accepted Answer

Magnesium sulfate

Answer

Morphine

Answer

Atropine

Answer

Lithium

Question 2

Aprepitant is used as:

Accepted Answer

Antiemetic

Answer

Antidepressant

Answer

Antihypertensive

Answer

Diuretic

Question 3

All of the following statements are true regarding ondansetron except?

Accepted Answer

It has significant drug interactions.

Answer

It is the antiemetic of choice for chemotherapy-induced vomiting.

Answer

It is a 5-HT3 receptor antagonist.

Answer

It may possess 5-HT4 agonism.

Question 4

All of the following drugs intensify gastrointestinal motility except?

Accepted Answer

Papaverine

Answer

Metoclopramide

Answer

Domperidone

Answer

Cisapride

Question 5

Why is glucose added to oral rehydration solution (ORS)?

Accepted Answer

To enhance the absorption of sodium and water.

Answer

To improve the palatability of the solution.

Answer

To increase the shelf life of the solution.

Answer

To improve the taste of the solution.

Question 6

What is the drug of choice for cisplatin-induced emesis?

Accepted Answer

Ondansetron

Answer

Metoclopramide

Answer

Domperidone

Answer

Octreotide

Question 7

Which of the following is NOT an effect of ranitidine when compared to cimetidine?

Accepted Answer

Anti-androgenic action

Answer

Action on H2 receptors

Answer

Given orally

Answer

Used with proton pump inhibitors

Question 8

What is true about the proton-pump inhibitor omeprazole?

Accepted Answer

CYP2C19 predicts efficacy.

Answer

Does not bind to plasma protein.

Answer

Oral bioavailability is 80%.

Answer

All of the above.

Question 9

What is the drug of choice for intractable hiccups?

Accepted Answer

Chlorpromazine

Answer

Metoclopramide

Answer

Haloperidol

Answer

Thioridazine

Question 10

Which drug is effective in ulcerative colitis?

Accepted Answer

5-aminosalicylic acid (5-ASA)

Answer

Corticosteroids

Answer

Sulfasalazine

Answer

Antibiotics

Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases — MCQs

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