Laxatives and Purging Agents — MCQs
Colonoscopy performed on a 25 year old woman with eating disorder showed dark brown to black pigmentary deposit in the lining of the large intestine. Histopathology of biopsy revealed pigment laden macrophages within the lamina propria. On probing, the woman revealed use of laxatives for 9 months to lose weight. What could be the probable laxative agent that could have caused these findings?
Portocaval encephalopathy is treated with
Constipation is a possible side effect of drugs taken by the oral route. Which of the following medications is least likely to cause constipation?
Which of the following is not considered a prokinetic agent?
Which is not a dietary fiber ?
Prucalopride is a
Which of the following drugs is NOT effective against chemotherapy-induced vomiting?
Which of the following drugs cause relaxation of the lower esophageal sphincter (LES)?
Alosetron is:
All the drugs given below can be used to protect gastric ulcer except?
Laxatives and Purging Agents Indian Medical PG Practice Questions and MCQs
Question 1: Colonoscopy performed on a 25 year old woman with eating disorder showed dark brown to black pigmentary deposit in the lining of the large intestine. Histopathology of biopsy revealed pigment laden macrophages within the lamina propria. On probing, the woman revealed use of laxatives for 9 months to lose weight. What could be the probable laxative agent that could have caused these findings?
- A. Castor oil
- B. Bisacodyl
- C. Senna (Correct Answer)
- D. Sorbitol
Explanation: ***Senna*** - Chronic use of **anthraquinone laxatives** like senna [1] leads to **melanosis coli**, characterized by dark brown pigment in the colon. - Histopathology reveals **pigment-laden macrophages** in the lamina propria, confirming melanosis coli. *Castor oil* - **Castor oil** is a stimulant laxative that acts on the small intestine but does not typically cause **melanosis coli**. - Its primary action is to increase fluid secretion and bowel motility, rather than pigment deposition. *Bisacodyl* - **Bisacodyl** is a stimulant laxative that works locally in the colon to increase fluid and electrolyte secretion and stimulate peristalsis. - It works on different pharmacological mechanisms and typically does not cause the characteristic **pigment-laden macrophages** that define melanosis coli. *Sorbitol* - **Sorbitol** is an osmotic laxative that works by drawing water into the colon, softening stools and promoting bowel movements. - It does not induce the characteristic **darkening of the colonic mucosa** or the specific histological changes observed in melanosis coli.
Question 2: Portocaval encephalopathy is treated with
- A. Diuretics
- B. Large amount of amino acids
- C. Emergency shunt surgery
- D. Lactulose (Correct Answer)
Explanation: ***Lactulose*** - **Lactulose** is a non-absorbable disaccharide that is metabolized by colonic bacteria, producing organic acids that **lower colonic pH**. - This acidic environment promotes the conversion of ammonia (NH3) to the non-absorbable ammonium ion (NH4+), which is then trapped in the colon and excreted in feces, thereby **reducing systemic ammonia levels**. [1] *Diuretics* - While diuretics are used in liver disease to manage **fluid retention** and **ascites**, they do not directly treat the underlying encephalopathy by removing nitrogenous waste. - In fact, some diuretics (e.g., loop diuretics) can exacerbate encephalopathy by causing **hypokalemia** and **alkalosis**, which favor the diffusion of ammonia into the central nervous system. *Large amount of amino acids* - A large intake of regular dietary **amino acids**, particularly aromatic amino acids, can actually worsen hepatic encephalopathy by increasing the production of nitrogenous waste products. [1] - In some cases, specialized amino acid formulations rich in **branched-chain amino acids** (BCAAs) are used, but a large, non-specific amount of amino acids is counterproductive. *Emergency shunt surgery* - Emergency shunt surgery is not a primary treatment for portosystemic encephalopathy and is generally reserved for managing **acute variceal bleeding** that cannot be controlled endoscopically. - While shunts can prevent recurrent variceal bleeding, they can also **worsen encephalopathy** by diverting more portal blood directly into the systemic circulation, bypassing the liver and increasing the exposure of the brain to toxins. [1]
Question 3: Constipation is a possible side effect of drugs taken by the oral route. Which of the following medications is least likely to cause constipation?
- A. promethazine
- B. loperamide
- C. docusate (Correct Answer)
- D. diphenhydramine
Explanation: ***docusate*** - **Docusate** is a **stool softener** and is actually used to prevent and treat constipation, making it the least likely to cause it. - It works by increasing the amount of water and fat the stool absorbs, making it easier to pass. *promethazine* - **Promethazine** is an antihistamine with **anticholinergic properties** that can slow down gut motility. - Reduced gastrointestinal motility is a common side effect of drugs with anticholinergic effects, leading to **constipation**. *loperamide* - **Loperamide** is an **opioid receptor agonist** that works by slowing down gut contractions. - It is specifically used as an **antidiarrheal medication**, and constipation is a well-known side effect of its action. *diphenhydramine* - **Diphenhydramine** is an antihistamine with significant **anticholinergic effects**. - Its anticholinergic action reduces intestinal motility and secretions, frequently causing **constipation**.
Question 4: Which of the following is not considered a prokinetic agent?
- A. Dopamine antagonist
- B. 5HT4 agonist
- C. Macrolides
- D. Diphenylmethane (Correct Answer)
Explanation: Diphenylmethane derivatives (e.g., bisacodyl, sodium picosulfate) are stimulant laxatives, not prokinetic agents. While they do increase colonic motility, they work by direct stimulation of the colonic mucosa and myenteric plexus, causing increased water secretion and peristalsis [3]. Prokinetic agents specifically enhance coordinated gastrointestinal motility through modulation of neurotransmitters (acetylcholine, dopamine, serotonin, motilin), whereas laxatives work through different mechanisms (osmotic effects, stimulation, bulk formation). Therefore, diphenylmethane derivatives are classified as laxatives, not prokinetics. Dopamine antagonist - Dopamine antagonists like metoclopramide and domperidone block D2 receptors in the chemoreceptor trigger zone and GI tract, enhancing acetylcholine release and promoting gastric emptying [2]. - They are commonly used as prokinetic agents and antiemetics [2]. 5HT4 agonist - 5HT4 agonists (e.g., cisapride, prucalopride) stimulate serotonin receptors in the enteric nervous system, increasing acetylcholine release and enhancing colonic motility [1]. - They are effective prokinetic agents for conditions like chronic constipation and gastroparesis [1]. Macrolides - Certain macrolide antibiotics, such as erythromycin, act as motilin receptor agonists at sub-antibiotic doses. - By mimicking motilin, they stimulate gastric and intestinal contractions (phase III of migrating motor complex), functioning as prokinetic agents.
Question 5: Which is not a dietary fiber ?
- A. Lignin
- B. Pectin
- C. Cellulose
- D. Lactulose (Correct Answer)
Explanation: ***Lactulose*** - **Lactulose is NOT a dietary fiber** - it is a synthetic disaccharide used pharmaceutically as an osmotic laxative and for treating hepatic encephalopathy. - Unlike true dietary fibers, lactulose is a manufactured drug, not a naturally occurring food component. - While it is fermented by colonic bacteria (similar to fiber), it does not meet the definition of dietary fiber. *Lignin* - Lignin is a complex aromatic polymer that provides structural support to plant cell walls. - It is classified as a non-polysaccharide dietary fiber that is largely indigestible by human enzymes. - Contributes to fecal bulk and is considered an insoluble fiber. *Pectin* - Pectin is a soluble dietary fiber found naturally in fruits, particularly in apple peels and citrus fruits. - Forms a gel when mixed with water, slowing gastric emptying and aiding digestion. - Beneficial for gut health and blood glucose regulation. *Cellulose* - Cellulose is the most abundant dietary fiber and a major structural component of plant cell walls. - An insoluble fiber composed of β-1,4-linked glucose polymers that cannot be digested by human enzymes. - Contributes to stool bulk and promotes regular bowel movements.
Question 6: Prucalopride is a
- A. 5HT4 agonist (Correct Answer)
- B. 5HT2b agonist
- C. 5HT2b antagonist
- D. 5HT1a partial agonist
Explanation: ***5HT4 agonist*** - **Prucalopride** is a highly selective, high-affinity **5HT4 receptor agonist** used to treat chronic idiopathic constipation. - Its activation of **5HT4 receptors** in the enteric nervous system stimulates gut motility and promotes colonic transit. *5HT2b agonist* - Agonism of **5HT2b receptors** is not the primary mechanism of action for prucalopride. - While 5HT2b receptors are present in the GI tract, their activation is not the therapeutic target for constipation relief with prucalopride. *5HT2b antagonist* - Prucalopride's therapeutic effect is due to agonism, not antagonism, of serotonin receptors. - Antagonism of **5HT2b receptors** would likely have different or even opposing effects on gut motility compared to prucalopride. *5HT1a partial agonist* - **5HT1a partial agonism** is characteristic of some anxiolytics and antidepressants, but not prucalopride. - This receptor subtype is primarily involved in central nervous system functions, not the direct regulation of gastrointestinal motility targeted by prucalopride.
Question 7: Which of the following drugs is NOT effective against chemotherapy-induced vomiting?
- A. Aprepitant
- B. Hyoscine (Correct Answer)
- C. Metoclopramide
- D. Ondansetron
Explanation: **Explanation:** The correct answer is **Hyoscine (Scopolamine)**. **1. Why Hyoscine is the correct answer:** Chemotherapy-induced nausea and vomiting (CINV) is primarily mediated by the stimulation of the **Chemoreceptor Trigger Zone (CTZ)** and the release of neurotransmitters like serotonin, substance P, and dopamine in the gut and brainstem. **Hyoscine** is an anticholinergic drug that acts primarily on the **vestibular system** (M1 receptors). It is highly effective for **motion sickness** but has no significant efficacy against the chemical triggers involved in CINV. **2. Why the other options are incorrect:** * **Aprepitant:** This is a **Neurokinin-1 (NK1) receptor antagonist**. It blocks the action of Substance P and is specifically indicated for the prevention of both acute and delayed phases of highly emetogenic chemotherapy. * **Metoclopramide:** A **D2 receptor antagonist** that also has 5-HT3 antagonistic properties at higher doses. It acts on the CTZ and enhances gastric emptying (prokinetic), making it useful in CINV. * **Ondansetron:** A **5-HT3 receptor antagonist**. It is the "gold standard" and first-line treatment for preventing acute emesis caused by chemotherapy by blocking serotonin receptors on vagal afferents and the CTZ. **Clinical Pearls for NEET-PG:** * **Drug of choice for Motion Sickness:** Hyoscine (administered as a transdermal patch behind the ear). * **Drug of choice for CINV:** 5-HT3 antagonists (e.g., Ondansetron). * **Drug of choice for Morning Sickness (Pregnancy):** Doxylamine + Pyridoxine. * **Drug of choice for Post-operative vomiting:** Ondansetron. * **Steroid use in CINV:** Dexamethasone is often added to Ondansetron/Aprepitant to potentiate their anti-emetic effects.
Question 8: Which of the following drugs cause relaxation of the lower esophageal sphincter (LES)?
- A. Nitrates, Histamine blockers, and Morphine
- B. Nitrates, Atropine, and Calcium channel blockers (Correct Answer)
- C. Nitrates, Histamine blockers, and Calcium channel blockers
- D. All of the above
Explanation: ### Explanation The tone of the lower esophageal sphincter (LES) is regulated by a complex interplay of myogenic, neural, and hormonal factors. Relaxation of the LES is a critical pharmacological concept because it can both cause Gastroesophageal Reflux Disease (GERD) as a side effect and be used therapeutically to treat conditions like Achalasia Cardia. **Why Option B is Correct:** * **Nitrates:** These act as nitric oxide (NO) donors. NO is the primary inhibitory neurotransmitter in the esophagus, leading to smooth muscle relaxation via the cGMP pathway. * **Atropine:** As an anticholinergic (muscarinic antagonist), it blocks the excitatory effect of acetylcholine on the LES, thereby reducing resting pressure. * **Calcium Channel Blockers (CCBs):** Drugs like Nifedipine inhibit the entry of calcium into smooth muscle cells, which is essential for muscle contraction, leading to significant LES relaxation. **Analysis of Incorrect Options:** * **Histamine Blockers (H2 Blockers):** Drugs like Ranitidine primarily decrease gastric acid secretion. They do not significantly decrease LES tone; in fact, they are used to *treat* the symptoms caused by a relaxed LES (GERD). * **Morphine:** Opioids generally increase the tone of various sphincters in the GI tract (e.g., Sphincter of Oddi) and do not typically cause LES relaxation as a primary mechanism. **High-Yield Clinical Pearls for NEET-PG:** * **Achalasia Cardia:** CCBs and Nitrates are used for medical management to decrease LES pressure, though pneumatic dilation or Myotomy are preferred. * **Drugs that INCREASE LES Tone:** Metoclopramide, Domperidone (Prokinetics), and Cholinergic agonists (Bethanechol). * **Lifestyle Factors:** Caffeine, fatty meals, chocolate, and smoking also decrease LES tone and should be avoided in GERD patients.
Question 9: Alosetron is:
- A. A 5HT1 receptor antagonist
- B. A 5HT2 receptor antagonist
- C. A 5HT3 receptor antagonist (Correct Answer)
- D. Analogues of somatostatin
Explanation: ### Explanation **Correct Option: C (A 5HT3 receptor antagonist)** **Mechanism of Action:** Alosetron is a potent and selective **5-HT3 receptor antagonist**. In the gastrointestinal tract, 5-HT3 receptors are located on enteric neurons and are responsible for regulating visceral pain, colonic transit, and gastrointestinal secretions. By blocking these receptors, Alosetron reduces abdominal pain, decreases intestinal secretions, and slows colonic transit time, making it effective for managing diarrhea-predominant symptoms. **Analysis of Incorrect Options:** * **Option A (5HT1 antagonist):** 5-HT1 receptors (specifically 5-HT1B/1D) are targets for Triptans (agonists) used in migraine. There is no major clinical role for 5-HT1 antagonists in GI disorders. * **Option B (5HT2 antagonist):** Drugs like Cyproheptadine block 5-HT2 receptors and are used for serotonin syndrome or as appetite stimulants, but they do not share Alosetron's clinical profile for IBS. * **Option D (Somatostatin analogues):** This refers to drugs like **Octreotide**, used for secretory diarrheas (e.g., VIPoma, Carcinoid syndrome) and variceal bleeding, not Alosetron. **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** Specifically approved for **severe, diarrhea-predominant Irritable Bowel Syndrome (IBS-D) in women** who have not responded to conventional therapy. * **Black Box Warning:** It is associated with a rare but serious risk of **Ischemic Colitis** and severe constipation. Due to these risks, it is often prescribed under a restricted safety program. * **Comparison:** While Alosetron (antagonist) is for IBS-D, **Prucalopride** (5-HT4 agonist) is used for chronic constipation.
Question 10: All the drugs given below can be used to protect gastric ulcer except?
- A. Colloidal bismuth salt
- B. Magnesium hydroxide (Correct Answer)
- C. Misoprostal
- D. Sucralfate
Explanation: ### Explanation The question asks to identify the drug that does **not** act as a "gastric mucosal protectant." **1. Why Magnesium Hydroxide is the Correct Answer:** Magnesium hydroxide is a **systemic/non-systemic antacid**. Its primary mechanism is the chemical neutralization of gastric hydrochloric acid (HCl), thereby increasing the gastric pH. While it reduces the aggressive factor (acid), it does not form a physical protective barrier over the ulcer base or enhance mucosal defense mechanisms. Therefore, it is classified as an antacid, not a mucosal protectant. **2. Why the other options are incorrect (Mucosal Protectants):** * **Sucralfate:** An aluminum salt of sulfated sucrose. In an acidic medium (pH < 4), it polymerizes into a sticky paste that binds selectively to the ulcer base (proteins/exudates), forming a physical barrier against acid and pepsin. * **Colloidal Bismuth Subcitrate (CBS):** It precipitates at low pH, coats the ulcer base, and detaches *H. pylori* from the gastric epithelium. It also stimulates prostaglandin synthesis and mucus/bicarbonate secretion. * **Misoprostol:** A PGE1 analogue. It acts as a cytoprotective agent by increasing mucus and bicarbonate secretion and improving mucosal blood flow. It also inhibits acid secretion via EP3 receptors on parietal cells. **3. NEET-PG High-Yield Pearls:** * **Sucralfate:** Requires an acidic medium for activation; hence, it should **not** be given with antacids, H2 blockers, or PPIs. * **Misoprostol:** Drug of choice for **NSAID-induced gastric ulcers** in patients who must continue NSAIDs. It is contraindicated in pregnancy (abortifacient). * **Bismuth salts:** Can cause black discoloration of stools and tongue (harmless) and are a component of Bismuth-based quadruple therapy for *H. pylori*. * **Antacid Side Effects:** Magnesium salts cause **diarrhea** ("Mg = Must Go"), while Aluminum salts cause **constipation**. They are often combined to balance bowel effects.
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