Antacids: Magnesium hydroxide mixture MCQs With Answer provides B. Pharm students a focused review of magnesium hydroxide as a liquid antacid—covering chemistry, mechanism, formulation, dosing, quality control, drug interactions and adverse effects. This concise, keyword-rich introduction emphasizes terms like antacids, magnesium hydroxide mixture, acid neutralizing capacity (ANC), formulation stability, hypermagnesemia, drug interactions and compounding considerations. Designed for exam preparation and practical pharmacy practice, the content balances pharmacology, pharmaceutics and regulatory testing to deepen understanding. Clear, clinical and formulation-focused questions help reinforce critical concepts required in B. Pharm courses. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary mechanism of action of magnesium hydroxide as an antacid?
- Systemic alkalinization by absorption and renal excretion
- Neutralization of gastric acid by hydroxide ions
- Coating the gastric mucosa to protect from acid
- Stimulating prostaglandin production to reduce acid secretion
Correct Answer: Neutralization of gastric acid by hydroxide ions
Q2. Magnesium hydroxide mixture is commonly referred to by which popular name in pharmacies?
- Simethicone suspension
- Milk of magnesia
- Aluminum phosphate gel
- Sodium bicarbonate solution
Correct Answer: Milk of magnesia
Q3. Which of the following best describes the chemical formula of magnesium hydroxide?
- MgO
- Mg(OH)2
- MgCO3
- MgCl2
Correct Answer: Mg(OH)2
Q4. Acid neutralizing capacity (ANC) of an antacid refers to:
- The rate of gastric emptying after administration
- The amount of acid neutralized per unit weight or volume
- The time taken for onset of symptom relief
- The ability to bind bile salts in intestine
Correct Answer: The amount of acid neutralized per unit weight or volume
Q5. Which adverse effect is most commonly associated with magnesium-containing antacids?
- Constipation
- Diarrhea
- Hypokalemia
- Hyperglycemia
Correct Answer: Diarrhea
Q6. A major contraindication for magnesium hydroxide use is:
- Renal insufficiency due to risk of hypermagnesemia
- Hypertension due to sodium load
- Peptic ulcer disease because it increases acid secretion
- Diabetes mellitus due to sugar content
Correct Answer: Renal insufficiency due to risk of hypermagnesemia
Q7. Which pharmacokinetic property of magnesium hydroxide is most relevant to its antacid action?
- High systemic bioavailability
- Local action in the stomach with minimal systemic absorption
- Hepatic metabolism to active metabolites
- Renal excretion after first-pass absorption
Correct Answer: Local action in the stomach with minimal systemic absorption
Q8. When formulating a magnesium hydroxide mixture, which excipient is commonly added to improve palatability?
- Glycerin
- Flavoring agents and sweeteners
- Sodium lauryl sulfate
- Calcium carbonate
Correct Answer: Flavoring agents and sweeteners
Q9. The neutralization reaction of magnesium hydroxide with hydrochloric acid produces:
- Magnesium chloride and water
- Magnesium oxide and carbon dioxide
- Magnesium sulfate and hydrogen gas
- Magnesium carbonate and water
Correct Answer: Magnesium chloride and water
Q10. Which laboratory test is commonly used to determine the acid neutralizing capacity of an antacid like magnesium hydroxide mixture?
- Titration with standard hydrochloric acid
- UV spectrophotometry at 254 nm
- High performance liquid chromatography
- Microbial limit test
Correct Answer: Titration with standard hydrochloric acid
Q11. Combination antacid products often include both magnesium and aluminum salts because:
- They synergistically increase gastric acid secretion
- Aluminum causes constipation and magnesium causes diarrhea, balancing GI effects
- Both increase systemic magnesium levels
- They reduce absorption of Vitamins
Correct Answer: Aluminum causes constipation and magnesium causes diarrhea, balancing GI effects
Q12. Which of the following interactions is most important when a patient is taking tetracyclines along with magnesium hydroxide?
- Magnesium enhances tetracycline absorption
- Magnesium forms insoluble chelates with tetracyclines reducing absorption
- Tetracyclines potentiate the laxative effect of magnesium
- No clinically significant interaction exists
Correct Answer: Magnesium forms insoluble chelates with tetracyclines reducing absorption
Q13. The onset of action of magnesium hydroxide mixture when taken orally is typically:
- Within minutes to 30 minutes
- Several hours later
- After 24 hours
- Only after repeated dosing for a week
Correct Answer: Within minutes to 30 minutes
Q14. In compounding a stable magnesium hydroxide oral suspension, which pH range is typically targeted to maintain stability and palatability?
- Highly acidic (pH 1–2)
- Neutral to slightly alkaline (pH 7–9)
- Extremely alkaline (pH >12)
- Strongly buffered at pH 4–5
Correct Answer: Neutral to slightly alkaline (pH 7–9)
Q15. Overuse of magnesium hydroxide can lead to which electrolyte disturbance?
- Hypomagnesemia
- Hypermagnesemia
- Hyponatremia
- Hyperchloremia
Correct Answer: Hypermagnesemia
Q16. Which quality control test specifically assesses the uniformity of a liquid magnesium hydroxide mixture?
- Assay for active content after shaking (content uniformity)
- Friability
- Disintegration time
- Dry content by loss on drying
Correct Answer: Assay for active content after shaking (content uniformity)
Q17. Magnesium hydroxide is classified pharmacologically as which type of agent?
- H2 receptor antagonist
- Proton pump inhibitor
- Antacid
- Gastric mucosal protector
Correct Answer: Antacid
Q18. Which patient population requires dose adjustment or caution when administering magnesium hydroxide?
- Patients with normal renal function
- Pregnant women in third trimester only
- Patients with renal impairment
- Young adults aged 18–25 only
Correct Answer: Patients with renal impairment
Q19. The typical role of magnesium hydroxide in antacid therapy compared to sodium bicarbonate is:
- Provides rapid systemic alkalosis
- Acts locally with lower risk of systemic alkalosis
- Releases CO2 to relieve bloating
- Has stronger buffering capacity per mole than bicarbonate
Correct Answer: Acts locally with lower risk of systemic alkalosis
Q20. Which adverse cardiovascular effect can occur with severe hypermagnesemia from excessive magnesium hydroxide?
- Bradycardia and hypotension
- Supraventricular tachycardia
- Hypertension and tachycardia
- Left ventricular hypertrophy
Correct Answer: Bradycardia and hypotension
Q21. For pediatric dosing of milk of magnesia, which consideration is most important?
- Use adult dose scaled only by age
- Ensure appropriate weight-based dosing and avoid repeated high doses
- Mix with alkaline beverages to enhance effect
- Administer only with dairy products
Correct Answer: Ensure appropriate weight-based dosing and avoid repeated high doses
Q22. Which analytical method can be used to quantify magnesium ion concentration in a magnesium hydroxide mixture?
- Titration with EDTA (complexometric titration)
- Flame photometry for sodium
- Infrared spectroscopy for organics
- Bacterial endotoxin test
Correct Answer: Titration with EDTA (complexometric titration)
Q23. The buffering capacity of an antacid influences:
- Only the taste of the formulation
- How much the pH changes when acid is added
- The ability to absorb lipophilic drugs
- The color of the liquid
Correct Answer: How much the pH changes when acid is added
Q24. Which clinical condition is magnesium hydroxide most appropriate to relieve?
- Acute myocardial infarction
- Gastric hyperacidity and heartburn
- Chronic renal failure without supervision
- Severe peptic ulcer bleeding
Correct Answer: Gastric hyperacidity and heartburn
Q25. When assessing the stability of a magnesium hydroxide suspension, which parameter is most indicative of physical stability?
- Color only
- Viscosity, sedimentation and redispersibility
- UV absorption at 210 nm
- Microbial content only
Correct Answer: Viscosity, sedimentation and redispersibility
Q26. Which excipient is often used as a suspending agent in magnesium hydroxide oral mixtures?
- Hydroxypropyl methylcellulose (HPMC) or xanthan gum
- Sodium chloride
- Calcium carbonate
- Magnesium stearate
Correct Answer: Hydroxypropyl methylcellulose (HPMC) or xanthan gum
Q27. A pharmacist counsels a patient to separate doses of magnesium hydroxide and ciprofloxacin by how many hours to reduce interaction?
- No separation is necessary
- At least 2 hours before or 4–6 hours after ciprofloxacin
- Only 15 minutes difference
- Always take together for synergy
Correct Answer: At least 2 hours before or 4–6 hours after ciprofloxacin
Q28. In USP monographs, the assay of magnesium hydroxide often involves titration against:
- Sodium hydroxide
- Standard hydrochloric acid
- Silver nitrate
- Potassium permanganate
Correct Answer: Standard hydrochloric acid
Q29. Which of the following is a systemic effect of excessive magnesium absorption?
- Increased deep tendon reflexes
- Depressed neuromuscular transmission leading to decreased reflexes
- Hyperactivity and tremors
- Increased gastric acid secretion
Correct Answer: Depressed neuromuscular transmission leading to decreased reflexes
Q30. When designing labeling for an over-the-counter magnesium hydroxide mixture, which warning is essential?
- May cause permanent tooth discoloration
- Avoid use in severe renal impairment unless under medical supervision
- Never take with any other oral medicine
- Must be refrigerated at all times
Correct Answer: Avoid use in severe renal impairment unless under medical supervision
Q31. Which statement about the onset and duration of antacid effect for magnesium hydroxide is correct?
- Onset slow, duration very short (<10 minutes)
- Rapid onset, moderate duration (up to a few hours)
- Onset delayed until systemic absorption occurs
- Duration is indefinite with single dose
Correct Answer: Rapid onset, moderate duration (up to a few hours)
Q32. The presence of carbonate or bicarbonate in an antacid formulation can lead to which unwanted effect compared to magnesium hydroxide alone?
- Increased risk of systemic alkalosis and CO2 evolution leading to belching
- Reduced palatability only
- Complete inactivation of magnesium
- Increased risk of hyperglycemia
Correct Answer: Increased risk of systemic alkalosis and CO2 evolution leading to belching
Q33. In pharmacology exams, the term ‘milk of magnesia’ specifically indicates:
- A solid tablet of magnesium hydroxide
- An aqueous suspension of magnesium hydroxide
- A magnesium-containing chewable candy
- An injectable magnesium solution
Correct Answer: An aqueous suspension of magnesium hydroxide
Q34. Which factor increases the risk of magnesium toxicity from antacids?
- Concurrent use of loop diuretics only
- Impaired renal excretion of magnesium
- High dietary calcium intake
- Administration with meals
Correct Answer: Impaired renal excretion of magnesium
Q35. Which test helps determine microbiological suitability of a magnesium hydroxide oral mixture?
- Viscosity measurement
- Microbial limit test and preservative efficacy test
- pH meter calibration only
- Moisture content by Karl Fischer only
Correct Answer: Microbial limit test and preservative efficacy test
Q36. The therapeutic use of magnesium hydroxide in constipation is primarily because it:
- Is a stimulant laxative
- Acts as an osmotic laxative by retaining water in the intestine
- Inhibits intestinal motility leading to constipation
- Blocks opioid receptors in gut
Correct Answer: Acts as an osmotic laxative by retaining water in the intestine
Q37. Which storage instruction is appropriate for commercial magnesium hydroxide mixtures?
- Store in well-closed container at controlled room temperature away from light
- Store frozen at -20°C
- Expose to direct sunlight to maintain potency
- Store under nitrogen to prevent oxidation
Correct Answer: Store in well-closed container at controlled room temperature away from light
Q38. In assessing drug interactions, magnesium hydroxide most commonly affects the absorption of which class of antibiotics?
- Beta-lactams
- Tetracyclines and fluoroquinolones
- Macrolides only
- Glycopeptides only
Correct Answer: Tetracyclines and fluoroquinolones
Q39. What is the impact of food on the antacid effect of magnesium hydroxide?
- Food completely prevents its action
- Food may delay onset but prolong duration of effect
- Food converts it into an acid
- Food increases systemic absorption dramatically
Correct Answer: Food may delay onset but prolong duration of effect
Q40. Which of the following is a correct compatibility consideration when packaging magnesium hydroxide mixtures?
- Avoid containers that react with alkaline mixtures, such as zinc or certain metals
- Use metal containers exclusively for stability
- Store in glass with cork stoppers only due to chemical reaction
- Packaging material is irrelevant for liquid antacids
Correct Answer: Avoid containers that react with alkaline mixtures, such as zinc or certain metals
Q41. Which lab parameter would be most important to monitor in a hospitalized patient receiving high doses of magnesium hydroxide?
- Serum magnesium concentration
- Serum potassium only
- Liver enzymes only
- Serum triglycerides
Correct Answer: Serum magnesium concentration
Q42. In formulation development, which preservative property is desirable for an oral magnesium hydroxide mixture?
- Microbial inhibitory activity compatible with pH and excipients
- Strong oxidizing action to degrade magnesium
- High volatility to evaporate quickly
- No microbial activity is necessary
Correct Answer: Microbial inhibitory activity compatible with pH and excipients
Q43. Which clinical symptom could indicate early magnesium toxicity?
- Tingling, nausea and lethargy
- Increased deep tendon reflexes and agitation
- Excessive sweating and fever
- Visual hallucinations only
Correct Answer: Tingling, nausea and lethargy
Q44. For a magnesium hydroxide oral suspension, which rheological property helps prevent rapid settling of particles?
- Low viscosity and Newtonian flow
- Appropriate increased viscosity and pseudoplastic behavior
- Completely solid gel formation
- Highly thixotropic irreversible gel
Correct Answer: Appropriate increased viscosity and pseudoplastic behavior
Q45. Which of the following best describes the role of magnesium hydroxide in combination with alginate formulations?
- Alginate neutralizes acid while magnesium increases foam formation
- Alginate forms a raft, magnesium neutralizes residual acid to reduce reflux symptoms
- Magnesium inhibits alginate activity
- They are never combined due to incompatibility
Correct Answer: Alginate forms a raft, magnesium neutralizes residual acid to reduce reflux symptoms
Q46. Which patient instruction is appropriate when advising about magnesium hydroxide antacid use?
- Take with all other oral medications to improve absorption
- Separate administration from certain antibiotics to avoid chelation
- Use daily without limit for chronic kidney disease
- Avoid fluids when taking the product
Correct Answer: Separate administration from certain antibiotics to avoid chelation
Q47. Which of the following is a pharmaceutic disadvantage of magnesium hydroxide compared to proton pump inhibitors?
- Produces systemic acid suppression for 48 hours
- Provides short-term symptomatic relief but does not reduce acid secretion long-term
- Causes irreversible inhibition of gastric H+/K+ ATPase
- Has stronger antisecretory action than PPIs
Correct Answer: Provides short-term symptomatic relief but does not reduce acid secretion long-term
Q48. During an in‑process control of a magnesium hydroxide suspension, failing redispersibility indicates:
- Excellent physical stability
- Potential formulation problems such as inadequate suspending agent or particle aggregation
- Low microbial contamination only
- Correct particle size distribution
Correct Answer: Potential formulation problems such as inadequate suspending agent or particle aggregation
Q49. Which lab test would detect inorganic contaminants such as heavy metals in a magnesium hydroxide mixture?
- Atomic absorption spectroscopy (AAS)
- HPLC for organic impurities
- Viscosity measurement
- pH titration
Correct Answer: Atomic absorption spectroscopy (AAS)
Q50. For exam preparation, which concept best summarizes the therapeutic profile of magnesium hydroxide mixtures?
- They are systemic antacid prodrugs requiring metabolic activation
- They are local, rapid-acting antacids with osmotic laxative effects and potential interactions in renal impairment
- They are primary gastroprotective agents preventing Helicobacter pylori infection
- They are the preferred long-term treatment for Zollinger-Ellison syndrome
Correct Answer: They are local, rapid-acting antacids with osmotic laxative effects and potential interactions in renal impairment
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