Cathartics: Bentonite is a focused topic for B. Pharm students exploring clay-based cathartics, formulation roles and pharmacological behavior. Bentonite, a smectite (montmorillonite) clay, is valued for its high cation-exchange capacity, swelling and strong adsorbent properties that influence laxative and suspending actions in dosage forms. This introduction covers mechanism of action, pharmaceutical applications, formulation considerations, stability, quality control tests, drug–excipient interactions, adverse effects and regulatory safety. Understanding bentonite’s physicochemical attributes and its role among cathartics and adsorbents is essential for formulation design, therapeutic use and mitigating drug absorption issues. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary mineralogical component of bentonite clay?
- Kaolinite
- Montmorillonite
- Illite
- Chlorite
Correct Answer: Montmorillonite
Q2. Bentonite belongs to which group of clays?
- Kaolin group
- Smectite group
- Chlorite group
- Vermiculite group
Correct Answer: Smectite group
Q3. The high swelling capacity of bentonite is primarily due to:
- Its crystalline quartz content
- Layered structure with interlayer water and exchangeable cations
- High organic matter content
- Metal oxide coatings
Correct Answer: Layered structure with interlayer water and exchangeable cations
Q4. Which property makes bentonite useful as a suspending agent in oral suspensions?
- Low viscosity
- Thixotropic behavior and swelling
- Strong alkalinity
- High solubility in water
Correct Answer: Thixotropic behavior and swelling
Q5. Bentonite’s cation exchange capacity (CEC) influences which pharmaceutical attribute?
- Color only
- Adsorption of drugs and ions
- Evaporation rate
- Melting point
Correct Answer: Adsorption of drugs and ions
Q6. In pharmacopeial preparations, “bentonite magma” refers to:
- A dry powder used in tablets
- An aqueous suspension of bentonite
- An oleaginous ointment base
- A concentrated tincture
Correct Answer: An aqueous suspension of bentonite
Q7. Which ion commonly occurs in bentonite interlayers and affects swelling?
- Fe3+
- Na+ and Ca2+
- Cl-
- CO3^2-
Correct Answer: Na+ and Ca2+
Q8. The mechanism by which bentonite can exert a cathartic effect is mainly through:
- Osmotic draw of electrolytes from blood
- Lubrication of fecal mass only
- Adsorption of water and increase in fecal bulk leading to peristalsis
- Stimulation of enteric nervous system via chemical irritants
Correct Answer: Adsorption of water and increase in fecal bulk leading to peristalsis
Q9. Acid activation of bentonite is performed to:
- Decrease its surface area
- Increase its adsorptive capacity by removing impurities and opening pores
- Make it fully soluble in water
- Convert it to kaolinite
Correct Answer: Increase its adsorptive capacity by removing impurities and opening pores
Q10. Which pharmaceutical test assesses the swelling ability of bentonite?
- Loss on drying
- Swelling index (or sedimentation volume)
- Viscosity only
- Melting point determination
Correct Answer: Swelling index (or sedimentation volume)
Q11. A significant safety concern with oral bentonite preparations is:
- Systemic absorption causing liver toxicity
- Contamination with heavy metals such as lead and arsenic
- Immediate hypersensitivity in most patients
- Rapid renal excretion
Correct Answer: Contamination with heavy metals such as lead and arsenic
Q12. Bentonite can reduce the oral absorption of certain drugs by:
- Enhancing gastric emptying
- Adsorbing the drug onto its surface
- Inhibiting hepatic metabolism
- Increasing intestinal pH to inactivate drugs
Correct Answer: Adsorbing the drug onto its surface
Q13. Which of the following drugs is most likely to have reduced absorption if co-administered with bentonite?
- Paracetamol (acetaminophen)
- Tetracyclines
- Insulin (injectable)
- Inhaled salbutamol
Correct Answer: Tetracyclines
Q14. The layered structure of bentonite is composed mainly of:
- Silica tetrahedral and alumina octahedral sheets
- Pure carbon layers
- Sulfide sheets
- Polymeric organic chains
Correct Answer: Silica tetrahedral and alumina octahedral sheets
Q15. Which parameter is critical for quality control of bentonite used in pharmaceutical suspensions?
- Particle size distribution, swelling index and microbial limits
- Optical rotation only
- Boiling point
- Viscosity at 200°C
Correct Answer: Particle size distribution, swelling index and microbial limits
Q16. Bentonite is classified pharmaceutically as which type of excipient?
- Synthetic polymer
- Inorganic clay excipient with adsorbent/suspending properties
- Hydrophobic lubricant
- Preservative
Correct Answer: Inorganic clay excipient with adsorbent/suspending properties
Q17. Which of the following is NOT a typical application of bentonite in pharmacy?
- Suspending agent in oral suspensions
- Adsorbent in topical pastes
- Primary active analgesic in tablets
- Clarifying agent in some formulations
Correct Answer: Primary active analgesic in tablets
Q18. The term “thixotropy” in relation to bentonite suspensions means:
- The suspension becomes more viscous on shaking
- The suspension becomes less viscous on standing
- The suspension becomes less viscous on shaking and regenerates viscosity on standing
- The suspension is completely non-Newtonian with no practical relevance
Correct Answer: The suspension becomes less viscous on shaking and regenerates viscosity on standing
Q19. Which analytical method is commonly used to identify montmorillonite in a bentonite sample?
- Ultraviolet spectroscopy
- X-ray diffraction (XRD)
- Thin-layer chromatography
- Gas chromatography
Correct Answer: X-ray diffraction (XRD)
Q20. Excessive oral intake of adsorbent clays like bentonite may lead to which gastrointestinal issue?
- Severe diarrhea due to osmotic activity
- Constipation and potential intestinal obstruction
- Immediate ulceration of the stomach
- Systemic hypertension
Correct Answer: Constipation and potential intestinal obstruction
Q21. Which of the following best describes bentonite’s interaction with electrolytes in the gut?
- It completely dissociates and releases chloride
- It exchanges its interlayer cations (e.g., Na+, Ca2+) with ions in the gut
- It oxidizes electrolytes to gases
- It has no interaction with electrolytes
Correct Answer: It exchanges its interlayer cations (e.g., Na+, Ca2+) with ions in the gut
Q22. For formulation scientists, which factor is essential when dispersing bentonite in aqueous media?
- Maintaining anhydrous conditions
- Proper hydration and slow stirring to allow swelling
- Adding strong oxidizers immediately
- Heating to 200°C to dissolve it
Correct Answer: Proper hydration and slow stirring to allow swelling
Q23. Which of the following tests helps determine the ability of bentonite to form and maintain a stable suspension?
- Sedimentation volume and viscosity measurement
- pH only
- Boiling point elevation
- Flash point
Correct Answer: Sedimentation volume and viscosity measurement
Q24. Bentonite’s effect on drug bioavailability is mainly due to:
- Enzymatic degradation of the drug
- Physical adsorption and sequestration of the drug molecule
- Metabolic induction of cytochrome P450 enzymes
- Promotion of gastric acid secretion
Correct Answer: Physical adsorption and sequestration of the drug molecule
Q25. Which form of bentonite shows greater swelling: sodium bentonite or calcium bentonite?
- Calcium bentonite swells more
- Sodium bentonite swells more
- Both swell equally
- Neither swells in water
Correct Answer: Sodium bentonite swells more
Q26. Which impurity in bentonite is most relevant to regulatory safety limits in pharmaceuticals?
- Silica content only
- Heavy metals (lead, arsenic, mercury)
- Excessive color pigments
- Low organic carbon
Correct Answer: Heavy metals (lead, arsenic, mercury)
Q27. Bentonite can be used in topical formulations primarily as a:
- Permeation enhancer
- Absorbent and vehicle for pastes
- Systemic antimicrobial agent
- Sensitizing perfume base
Correct Answer: Absorbent and vehicle for pastes
Q28. Which of the following describes the effect of grinding/finely milling bentonite for use in oral formulations?
- Decreases surface area and reduces adsorption
- Increases surface area, enhancing swelling and adsorption but may affect rheology
- Converts it into soluble silica
- Removes all exchangeable cations
Correct Answer: Increases surface area, enhancing swelling and adsorption but may affect rheology
Q29. In the context of cathartics, which category best fits bentonite’s action?
- Contact stimulant cathartic
- Bulk-forming/adsorbent cathartic
- Osmotic saline cathartic
- Stool softener (surfactant) only
Correct Answer: Bulk-forming/adsorbent cathartic
Q30. Which excipient property should be monitored to prevent microbial growth in aqueous bentonite suspensions?
- Use of appropriate preservatives and pH control
- Ensuring the suspension is nutrient-rich
- Adding sugar as a carbon source
- Sterilizing at 300°C
Correct Answer: Use of appropriate preservatives and pH control
Q31. Which characterization technique provides information about bentonite surface area and porosity?
- BET (Brunauer–Emmett–Teller) nitrogen adsorption
- Mass spectrometry
- Polarimetry
- NMR of protons only
Correct Answer: BET (Brunauer–Emmett–Teller) nitrogen adsorption
Q32. Bentonite’s role in oral rehydration or diarrhea management is primarily due to:
- Supplying electrolytes
- Adsorbing toxins and microorganisms and reducing stool liquidity
- Direct antimicrobial systemic action
- Increasing gastric acid
Correct Answer: Adsorbing toxins and microorganisms and reducing stool liquidity
Q33. Which statement about bentonite’s solubility is correct?
- Bentonite is highly soluble in gastric acid
- Bentonite is insoluble and forms colloidal dispersions on hydration
- Bentonite dissolves in ethanol
- Bentonite sublimes on heating
Correct Answer: Bentonite is insoluble and forms colloidal dispersions on hydration
Q34. When formulating with bentonite, why is pH adjustment sometimes necessary?
- To make it fully volatile
- To optimize swelling, stability and preservative efficacy
- To convert it into an organic polymer
- To ensure it reacts with all drugs
Correct Answer: To optimize swelling, stability and preservative efficacy
Q35. Which of the following tests would detect contamination of bentonite with pathogenic microbes?
- Assay for silica
- Microbial limit testing
- FTIR spectroscopy
- Viscosity measurement
Correct Answer: Microbial limit testing
Q36. Bentonite interacts with which formulation component to potentially reduce the effectiveness of oral vaccines or antibiotics?
- Lipids only
- Antigens and antibiotic molecules via adsorption
- Flavoring agents only
- Synthetic polymers are unaffected
Correct Answer: Antigens and antibiotic molecules via adsorption
Q37. Which method is appropriate to reduce drug–bentonite interactions in a combined oral product?
- Co-administer drug with bentonite together to maximize interaction
- Use spacer dosing (separate administration times) or use coating to prevent adsorption
- Increase bentonite dose tenfold
- Remove the drug from the formulation entirely
Correct Answer: Use spacer dosing (separate administration times) or use coating to prevent adsorption
Q38. The presence of organic matter in bentonite may affect which property most directly?
- Electrical conductivity only
- Adsorptive capacity and color
- Transform it into a gas
- Make it magnetic
Correct Answer: Adsorptive capacity and color
Q39. Which pharmacopoeial parameter would be used to test for inorganic impurities in bentonite?
- Loss on drying
- Assay for heavy metals (heavy metal limit tests)
- Enzymatic activity assay
- Osmolarity measurement
Correct Answer: Assay for heavy metals (heavy metal limit tests)
Q40. In which dosage form is bentonite least likely to be used?
- Topical paste
- Oral suspension
- Parenteral injectable solution
- Capsule as a diluent
Correct Answer: Parenteral injectable solution
Q41. Which structural feature allows bentonite to adsorb organic molecules?
- Its non-porous dense crystal lattice
- Large specific surface area and interlayer space
- Only its color contributes to adsorption
- Its solubility in lipids
Correct Answer: Large specific surface area and interlayer space
Q42. Which statement about bentonite and electrolyte balance is TRUE when used as a cathartic?
- It causes massive systemic electrolyte loss like hyperosmotic laxatives
- It has negligible osmotic effect but may alter local ion exchange in gut lumen
- It enriches blood sodium levels directly
- It chelates systemic potassium causing hypokalemia directly
Correct Answer: It has negligible osmotic effect but may alter local ion exchange in gut lumen
Q43. Which processing parameter is critical to ensure reproducible rheology of bentonite suspensions?
- Mixing time, shear rate and hydration protocol
- Color matching
- Exposing to direct sunlight during manufacture
- Adding volatile solvents
Correct Answer: Mixing time, shear rate and hydration protocol
Q44. Which excipient incompatibility is commonly observed with bentonite in solid dosage forms?
- Strong interactions with ionic drugs leading to reduced availability
- Complete inertness with all excipients
- Spontaneous combustion when mixed
- Conversion into gelatin
Correct Answer: Strong interactions with ionic drugs leading to reduced availability
Q45. Which regulatory concern is most relevant when sourcing bentonite for oral pharmaceutical use?
- Ensuring batch-to-batch uniformity, purity and limits for elemental impurities
- Checking its flame point only
- Certifying it as sterile for injection
- Confirming it is food grade sugar
Correct Answer: Ensuring batch-to-batch uniformity, purity and limits for elemental impurities
Q46. Which of the following best describes how bentonite affects viscosity in a formulation?
- It always decreases viscosity
- It can increase viscosity due to network formation and swelling
- It converts liquid to gas reducing viscosity
- It has no impact on viscosity under any conditions
Correct Answer: It can increase viscosity due to network formation and swelling
Q47. In the context of drug delivery, which property of bentonite can be exploited for sustained release?
- Rapid dissolution in stomach
- Adsorptive binding and slow desorption of drugs
- Complete metabolic stability in bloodstream
- Volatility at room temperature
Correct Answer: Adsorptive binding and slow desorption of drugs
Q48. Which handling precaution is important for manufacturing personnel working with bentonite powder?
- No precautions needed; it is always safe
- Avoid inhalation of fine dust and use appropriate PPE
- Only ingest small amounts to test quality
- Store at high temperatures to sterilize
Correct Answer: Avoid inhalation of fine dust and use appropriate PPE
Q49. Which is a common method to reduce bentonite’s adsorption of a co-formulated drug?
- Increasing contact time deliberately
- Using surface coating on drug particles or employing spacer dosing
- Acidifying the drug to pH 1 always
- Drying the bentonite at 500°C with the drug
Correct Answer: Using surface coating on drug particles or employing spacer dosing
Q50. Which characteristic distinguishes sodium bentonite from calcium bentonite in pharmaceutical behavior?
- Sodium bentonite has greater swelling and dispersion in water compared to calcium bentonite
- Calcium bentonite is more soluble in ethanol than sodium bentonite
- Sodium bentonite is magnetic while calcium is not
- Both are identical in all physicochemical behaviors
Correct Answer: Sodium bentonite has greater swelling and dispersion in water compared to calcium bentonite
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.
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