Cathartics: Magnesium sulphate MCQs With Answer

Cathartics: Magnesium sulphate MCQs With Answer

Magnesium sulphate is an important osmotic cathartic frequently covered in B. Pharm pharmacology and therapeutics modules. This introduction explains its mechanism of action, therapeutic uses as a saline laxative and bowel prep, typical oral doses and onset, adverse effects like hypermagnesemia and dehydration, contraindications such as renal failure and intestinal obstruction, and key drug interactions. These concise, keyword-rich points help students understand pharmacodynamics, pharmacokinetics, monitoring and patient counseling. Ideal for revision before exams or practicals, this set focuses on clinical and pharmaceutical aspects relevant to coursework and pharmacy practice. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary mechanism of action of magnesium sulphate when used as a cathartic?

• Stimulates opioid receptors in the gut
• Acts as a bulk-forming fiber
• Provides osmotic effect drawing water into the intestinal lumen
• Inhibits acetylcholinesterase in the enteric nervous system

Correct Answer: Provides osmotic effect drawing water into the intestinal lumen

Q2. Which of the following best classifies magnesium sulphate among laxatives?

• Stimulant laxative
• Osmotic cathartic
• Bulk-forming laxative
• Stool softener

Correct Answer: Osmotic cathartic

Q3. Typical oral dose range of magnesium sulphate (Epsom salt) for adult catharsis is closest to which of the following?

• 0.5–1 g
• 2–5 g
• 10–30 g
• 50–100 g

Correct Answer: 10–30 g

Q4. Usual onset of action for oral magnesium sulphate as a cathartic is:

• 5–10 minutes
• 30 minutes to 6 hours
• 24–48 hours
• 3–5 days

Correct Answer: 30 minutes to 6 hours

Q5. Which patient condition is an absolute contraindication to oral magnesium sulphate catharsis?

• Mild constipation
• Renal failure with oliguria
• Hypertension
• Controlled diabetes mellitus

Correct Answer: Renal failure with oliguria

Q6. A key adverse effect of excessive magnesium sulphate ingestion is:

• Hyperkalemia
• Hypermagnesemia leading to hypotonia and respiratory depression
• Hypoglycemia
• Hypercalcemia

Correct Answer: Hypermagnesemia leading to hypotonia and respiratory depression

Q7. Which laboratory test is most important to monitor in patients at risk after magnesium sulphate administration?

• Serum sodium
• Serum magnesium
• Liver function tests
• Serum amylase

Correct Answer: Serum magnesium

Q8. Compared to magnesium hydroxide (milk of magnesia), magnesium sulphate is:

• Less osmotically active per gram
• More commonly used for topical dermatologic application only
• A soluble salt historically used as an oral saline laxative with strong osmotic effect
• An opioid agonist

Correct Answer: A soluble salt historically used as an oral saline laxative with strong osmotic effect

Q9. Which of the following is a common gastrointestinal adverse effect of magnesium sulphate?

• Constipation
• Abdominal cramping and diarrhea
• Peptic ulceration
• Esophageal strictures

Correct Answer: Abdominal cramping and diarrhea

Q10. Why is magnesium sulphate contraindicated in complete intestinal obstruction?

• It is absorbed and causes systemic toxicity in obstruction
• It can worsen distension and risk of perforation due to osmotic fluid influx
• It causes irreversible ileus
• It neutralizes gastric acid therefore increasing infection risk

Correct Answer: It can worsen distension and risk of perforation due to osmotic fluid influx

Q11. Which route of administration is commonly used for magnesium sulphate when employed as a cathartic?

• Intravenous
• Oral dissolved in water
• Intramuscular
• Subcutaneous

Correct Answer: Oral dissolved in water

Q12. In which of the following situations is magnesium sulphate useful as a bowel preparation?

• Emergency treatment of myocardial infarction
• Preparation for diagnostic colonoscopy
• Long-term maintenance therapy for chronic constipation
• Treatment of acute pancreatitis

Correct Answer: Preparation for diagnostic colonoscopy

Q13. Which drug interaction is important to consider when giving magnesium sulphate with aminoglycoside antibiotics?

• Magnesium reduces aminoglycoside levels
• Increased risk of neuromuscular blockade and respiratory depression
• Aminoglycosides enhance magnesium absorption
• No clinically relevant interaction

Correct Answer: Increased risk of neuromuscular blockade and respiratory depression

Q14. The main route of elimination of absorbed magnesium is:

• Hepatic metabolism
• Renal excretion
• Biliary excretion
• Pulmonary exhalation

Correct Answer: Renal excretion

Q15. Which electrolyte disturbance may result from aggressive use of magnesium sulphate?

• Hyponatremia only
• Hypomagnesemia
• Hypermagnesemia and secondary hypocalcemia
• Hyperkalemia only

Correct Answer: Hypermagnesemia and secondary hypocalcemia

Q16. Which patient counseling point is appropriate for oral magnesium sulphate use?

• Take with large amounts of milk to enhance effect
• Expect onset within 30 minutes to a few hours and maintain hydration
• Use daily for months for weight loss
• Co-administer with antacids to reduce side effects

Correct Answer: Expect onset within 30 minutes to a few hours and maintain hydration

Q17. Which of the following signs suggests early magnesium toxicity?

• Hyperreflexia
• Bradycardia and hypotension; diminished deep tendon reflexes
• Mydriasis and hyperactivity
• Polyuria with increased reflexes

Correct Answer: Bradycardia and hypotension; diminished deep tendon reflexes

Q18. In patients with significant renal impairment, magnesium sulphate as an oral cathartic should be:

• Used at double the usual dose
• Avoided due to risk of accumulation and hypermagnesemia
• Preferred because it is safer than lactulose
• Administered intramuscularly instead

Correct Answer: Avoided due to risk of accumulation and hypermagnesemia

Q19. Which formulation of magnesium is most commonly known as “Epsom salt”?

• Magnesium carbonate
• Magnesium sulphate heptahydrate
• Magnesium oxide
• Magnesium citrate

Correct Answer: Magnesium sulphate heptahydrate

Q20. Compared with stimulant laxatives like senna, magnesium sulphate primarily works by:

• Stimulating enteric nerves directly
• Increasing fecal bulk through fiber expansion
• Osmotically retaining water in the lumen
• Softening stool via surfactant action

Correct Answer: Osmotically retaining water in the lumen

Q21. Which monitoring is essential if large doses of magnesium sulphate are used for bowel preparation?

• Daily ECG only
• Serum magnesium, renal function, and clinical monitoring of reflexes and respiration
• Serum bilirubin
• Chest X-ray

Correct Answer: Serum magnesium, renal function, and clinical monitoring of reflexes and respiration

Q22. Which of the following is a pharmacokinetic property of magnesium sulphate after oral administration?

• Complete absorption in the stomach
• Poor and variable systemic absorption with most retained in gut lumen
• Metabolized extensively by gut flora to active metabolites
• Converted to elemental magnesium and stored in liver

Correct Answer: Poor and variable systemic absorption with most retained in gut lumen

Q23. Which coexisting condition increases the risk of magnesium accumulation after oral magnesium sulphate?

• Hyperthyroidism
• Chronic kidney disease
• Iron deficiency anemia
• Asthma well-controlled on inhalers

Correct Answer: Chronic kidney disease

Q24. Which intravenous use of magnesium sulphate is distinct from its cathartic use?

• Treatment of acute hypercholesterolemia
• Management of eclampsia and severe pre-eclampsia
• Long-term treatment of chronic constipation
• Topical treatment for eczema

Correct Answer: Management of eclampsia and severe pre-eclampsia

Q25. Which of the following is a potential cardiovascular effect of systemic magnesium excess?

• Hypertension and tachycardia
• Hypotension, bradyarrhythmias, and cardiac conduction defects
• Increased myocardial contractility
• Vasospasm and hypertension crisis

Correct Answer: Hypotension, bradyarrhythmias, and cardiac conduction defects

Q26. Which co-administered oral drug’s absorption can be impaired by concurrent magnesium salts?

• Penicillin G
• Tetracyclines and fluoroquinolones due to formation of insoluble complexes
• Metformin
• Insulin

Correct Answer: Tetracyclines and fluoroquinolones due to formation of insoluble complexes

Q27. In pediatric dosing, magnesium sulphate as a laxative should be used with caution because:

• Children excrete magnesium more rapidly than adults
• Smaller margin of safety and higher risk of electrolyte disturbances and dehydration
• It is ineffective in children
• It causes permanent teeth staining

Correct Answer: Smaller margin of safety and higher risk of electrolyte disturbances and dehydration

Q28. Which adverse effect would prompt immediate cessation and evaluation after oral magnesium sulphate?

• Mild flatulence
• Marked muscle weakness and depressed respiration
• Transitory thirst
• Temporary taste alteration

Correct Answer: Marked muscle weakness and depressed respiration

Q29. For laboratory interpretation, normal serum magnesium is approximately which range?

• 0.7–1.1 mmol/L (≈1.7–2.7 mg/dL)
• 10–12 mmol/L
• 0.01–0.05 mmol/L
• 5–7 mmol/L

Correct Answer: 0.7–1.1 mmol/L (≈1.7–2.7 mg/dL)

Q30. Which formulation is least likely to be used as an oral cathartic?

• Magnesium sulphate powder dissolved in water
• Liquid magnesium sulphate solution for irrigation
• Enteric-coated magnesium capsule designed for slow release
• Magnesium citrate solution

Correct Answer: Enteric-coated magnesium capsule designed for slow release

Q31. Which statement about the use of magnesium sulphate in pregnancy is correct?

• Oral magnesium sulphate catharsis is safe in all pregnant women without monitoring
• IV magnesium sulphate is used for eclampsia; oral cathartic use should be cautious and monitored
• Magnesium salts are completely contraindicated in pregnancy
• Magnesium sulphate increases uterine contractions and is used to induce labor

Correct Answer: IV magnesium sulphate is used for eclampsia; oral cathartic use should be cautious and monitored

Q32. Which sign differentiates severe hypermagnesemia from mild side effects?

• Mild nausea and abdominal discomfort
• Loss of deep tendon reflexes and respiratory paralysis
• Transcient headache
• Slight sweating

Correct Answer: Loss of deep tendon reflexes and respiratory paralysis

Q33. Which of the following is an evidence-based indication for magnesium sulphate as a cathartic?

• Routine daily bowel regulation for healthy adults
• Short-term relief of acute constipation and bowel cleansing before procedures
• Treatment of inflammatory bowel disease maintenance
• First-line therapy for irritable bowel syndrome

Correct Answer: Short-term relief of acute constipation and bowel cleansing before procedures

Q34. When advising a patient preparing for colonoscopy, which instruction about magnesium sulphate is correct?

• Take the dose immediately before bedtime and expect bowel movement in 24–48 hours
• Follow recommended dose and ensure adequate oral fluids to avoid dehydration
• Combine with diuretics to enhance effect
• Avoid clear fluids during the preparation

Correct Answer: Follow recommended dose and ensure adequate oral fluids to avoid dehydration

Q35. Which of the following best describes systemic absorption of orally administered magnesium sulphate?

• Rapid and complete with high bioavailability
• Minimal and variable; increases with dose and renal impairment
• Dependent on hepatic activation
• Occurs only after colonic bacteria metabolize the salt

Correct Answer: Minimal and variable; increases with dose and renal impairment

Q36. In a patient taking digoxin, administration of magnesium sulphate may:

• Increase digoxin levels directly
• Potentiate digoxin toxicity by causing electrolyte disturbances (e.g., hypokalemia/hypermagnesemia)
• Eliminate digoxin via chelation
• Enhance digoxin absorption

Correct Answer: Potentiate digoxin toxicity by causing electrolyte disturbances (e.g., hypokalemia/hypermagnesemia)

Q37. The physicochemical property that makes magnesium sulphate effective as a saline laxative is:

• High lipid solubility
• High osmotic activity in the intestinal lumen
• Strong acid-neutralizing capacity
• Activation of proteolytic enzymes

Correct Answer: High osmotic activity in the intestinal lumen

Q38. Which of the following is the correct antidote for severe magnesium toxicity?

• Oral calcium carbonate
• Intravenous calcium gluconate
• Intramuscular insulin
• Activated charcoal

Correct Answer: Intravenous calcium gluconate

Q39. Which patient would require extreme caution before using magnesium sulphate as an oral cathartic?

• Young adult with occasional constipation and normal renal function
• Elderly patient with chronic kidney disease stage 4
• Healthy pregnant woman in first trimester
• Patient using topical antifungal cream

Correct Answer: Elderly patient with chronic kidney disease stage 4

Q40. Which statement about combination use of magnesium sulphate with loop diuretics is correct?

• Loop diuretics protect against hypermagnesemia
• Loop diuretics may increase magnesium excretion and alter electrolyte balance; monitoring required
• They neutralize each other and can be co-administered without concern
• Loop diuretics cause irreversible binding to magnesium salts

Correct Answer: Loop diuretics may increase magnesium excretion and alter electrolyte balance; monitoring required

Q41. Which gastrointestinal pathology increases risk when using an osmotic cathartic like magnesium sulphate?

• Peptic ulcer disease without obstruction
• Inflammatory bowel disease with active colitis or megacolon
• Gastritis controlled by PPI
• Hemorrhoids

Correct Answer: Inflammatory bowel disease with active colitis or megacolon

Q42. Which description accurately contrasts magnesium sulphate with stimulant laxatives regarding tolerance?

• Magnesium sulphate causes rapid tolerance and dependence
• Stimulant laxatives are more associated with habituation; osmotic cathartics less so with short-term use
• Both cause permanent loss of bowel function after one use
• Neither affects bowel motility over time

Correct Answer: Stimulant laxatives are more associated with habituation; osmotic cathartics less so with short-term use

Q43. What is an important pharmacy practice consideration when dispensing magnesium sulphate powder for oral use?

• Advise the patient to take without water
• Provide clear instructions on dilution, dose, timing and warn about dehydration and interactions
• Recommend mixing with milk to improve taste
• Label as safe for use in renal failure without monitoring

Correct Answer: Provide clear instructions on dilution, dose, timing and warn about dehydration and interactions

Q44. Which feature differentiates magnesium citrate from magnesium sulphate as cathartics?

• Magnesium citrate is not osmotic
• Magnesium citrate is often palatable and commonly used for bowel prep; magnesium sulphate historically used as Epsom salt
• Magnesium sulphate has no systemic absorption
• Magnesium citrate causes permanent electrolyte loss only

Correct Answer: Magnesium citrate is often palatable and commonly used for bowel prep; magnesium sulphate historically used as Epsom salt

Q45. Which professional action is required if a patient develops signs of magnesium toxicity after oral cathartic use?

• Continue cathartic and observe at home
• Stop magnesium salt, assess airway/breathing/circulation, measure serum magnesium, and give IV calcium if severe
• Administer oral antidiarrheal medication immediately
• Encourage more fluid and outpatient follow-up in one week

Correct Answer: Stop magnesium salt, assess airway/breathing/circulation, measure serum magnesium, and give IV calcium if severe

Q46. Which pharmacological property explains why magnesium sulphate produces watery stools?

• Inhibition of gastric acid secretion
• Osmotic retention of water and stimulation of intestinal motility
• Increased bile acid secretion
• Enhanced protein digestion

Correct Answer: Osmotic retention of water and stimulation of intestinal motility

Q47. For research and formulation, which stability consideration is relevant to magnesium sulphate powder?

• It is highly volatile and requires refrigeration
• It is hygroscopic; proper packaging to protect from moisture is important
• It rapidly oxidizes on exposure to air
• It converts to elemental magnesium at room temperature

Correct Answer: It is hygroscopic; proper packaging to protect from moisture is important

Q48. Which clinical sign suggests progression from hypermagnesemia to life-threatening toxicity?

• Mild nausea only
• Loss of deep tendon reflexes progressing to respiratory depression and cardiac arrest
• Transient dizziness that resolves spontaneously
• Mild headache without neurologic findings

Correct Answer: Loss of deep tendon reflexes progressing to respiratory depression and cardiac arrest

Q49. In overdoses of magnesium salts, beside IV calcium, which supportive measure is often indicated?

• Forced diuresis and dialysis in severe renal failure
• Immediate gastric lavage only
• High-dose oral sodium bicarbonate
• Topical cooling

Correct Answer: Forced diuresis and dialysis in severe renal failure

Q50. From a pharmacology exam perspective, which statement is most accurate regarding educational focus on magnesium sulphate as a cathartic?

• Only memorizing dose is sufficient for clinical use
• Understanding mechanism, dosing, onset, contraindications, monitoring and interactions is essential for safe pharmacy practice
• Clinical monitoring is irrelevant for over-the-counter use
• Magnesium sulphate is obsolete and not covered in modern curricula

Correct Answer: Understanding mechanism, dosing, onset, contraindications, monitoring and interactions is essential for safe pharmacy practice

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com