Preparation of deflocculated suspensions MCQs With Answer

Introduction: Preparation of deflocculated suspensions is a core competency in pharmaceutics for B. Pharm students. In deflocculated systems, particles remain discrete due to high zeta potential and low electrolyte compression, giving slower sedimentation but a higher risk of caking. Success requires thoughtful preformulation, efficient wetting and dispersion, controlled particle size reduction, appropriate viscosity modifiers and rheology (pseudoplastic, thixotropic), and careful control of pH, ionic strength, and surfactant choice. Key concepts include Stokes’ law, DLVO theory, sedimentation volume, redispersibility, Ostwald ripening, homogenization/milling, suspending agents (e.g., NaCMC, xanthan), and buffer selection. This introduction emphasizes practical steps, stability testing, and excipient compatibility to achieve uniform dosing and physical stability. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which statement best describes a deflocculated suspension?

• Particles are weakly clustered into loose networks that settle rapidly but redisperse easily
• Particles remain as discrete units with high repulsive forces and settle slowly with caking risk
• Particles are fused into aggregates that never settle
• Particles float due to density lower than the vehicle regardless of particle size

Correct Answer: Particles remain as discrete units with high repulsive forces and settle slowly with caking risk

Q2. In deflocculated suspensions, a high magnitude of zeta potential is desirable because it:

• Promotes controlled floc formation
• Increases van der Waals attraction
• Enhances electrostatic repulsion and maintains dispersion
• Eliminates the need for wetting agents

Correct Answer: Enhances electrostatic repulsion and maintains dispersion

Q3. According to Stokes’ law, sedimentation velocity in a deflocculated suspension decreases when:

• Particle diameter increases and viscosity decreases
• Particle diameter decreases and viscosity increases
• Density difference between solid and liquid increases
• Zeta potential decreases

Correct Answer: Particle diameter decreases and viscosity increases

Q4. Which strategy best maintains deflocculation during formulation?

• Increase ionic strength to compress the double layer
• Adjust pH away from the isoelectric point of the particle surface
• Add electrolytes to reduce surface charge
• Introduce polyvalent counterions to neutralize charge

Correct Answer: Adjust pH away from the isoelectric point of the particle surface

Q5. The most appropriate wetting approach for hydrophobic drug powders in aqueous deflocculated suspensions is to:

• Pre-wet with a nonionic surfactant solution before dispersion
• Use high levels of electrolytes to increase wettability
• Add oil to reduce surface energy
• Increase pH beyond the drug’s degradation range

Correct Answer: Pre-wet with a nonionic surfactant solution before dispersion

Q6. Which class of excipients primarily provides structured vehicles that reduce sedimentation without inducing flocculation?

• Electrolytes (e.g., sodium chloride)
• Suspending agents (e.g., sodium CMC, xanthan gum, HPMC)
• Antioxidants (e.g., BHT)
• Flavoring agents

Correct Answer: Suspending agents (e.g., sodium CMC, xanthan gum, HPMC)

Q7. The preferred rheological behavior for pourable deflocculated suspensions intended for oral use is:

• Dilatant and non-thixotropic
• Newtonian throughout the shear range
• Pseudoplastic with mild thixotropy
• Highly elastic (solid-like)

Correct Answer: Pseudoplastic with mild thixotropy

Q8. Which processing step is most effective for narrowing particle size distribution in a deflocculated suspension?

• Low-speed propeller mixing
• High-shear homogenization or wet media milling
• Static mixing only
• Standing to allow gravitational separation

Correct Answer: High-shear homogenization or wet media milling

Q9. DLVO theory in suspension stability refers to the balance between:

• Hydrogen bonding and ionic bonding
• Electrostatic repulsion and van der Waals attraction
• Shear thinning and shear thickening
• Osmotic pressure and capillary action

Correct Answer: Electrostatic repulsion and van der Waals attraction

Q10. To maintain a deflocculated state, the buffer system should generally be formulated to:

• Provide high ionic strength to improve taste
• Minimize ionic strength while controlling pH
• Contain polyvalent cations to bridge particles
• Shift pH to the particle’s isoelectric point

Correct Answer: Minimize ionic strength while controlling pH

Q11. Which statement about sedimentation volume (F) is most accurate for deflocculated suspensions?

• F is typically larger than in flocculated systems
• F is often smaller, with higher caking risk if vehicle is not sufficiently structured
• F is always 1 regardless of formulation
• F cannot be measured in deflocculated systems

Correct Answer: F is often smaller, with higher caking risk if vehicle is not sufficiently structured

Q12. A key risk of excessive particle size reduction in deflocculated suspensions is:

• Reduced surface area leading to poor dissolution
• Ostwald ripening due to increased surface energy
• Instant gelation due to particle fusion
• Immediate microbial growth

Correct Answer: Ostwald ripening due to increased surface energy

Q13. Which surfactant class is preferred to maintain deflocculation with minimal impact on zeta potential?

• Nonionic surfactants (e.g., polysorbates)
• Cationic surfactants (e.g., CTAB)
• Anionic surfactants (e.g., SDS) at high ionic strength
• Zwitterionic surfactants with multivalent counterions

Correct Answer: Nonionic surfactants (e.g., polysorbates)

Q14. Which method best evaluates particle size distribution during suspension preparation?

• Polarimetry
• Laser diffraction
• UV-Vis spectroscopy at 254 nm
• Refractometry

Correct Answer: Laser diffraction

Q15. The most appropriate order of addition to prepare a deflocculated suspension is:

• Add dry powder directly to final vehicle under low shear
• Levigate powder with wetting agent, then disperse into structured vehicle
• Adjust pH after bottling
• Add preservative last and do not mix

Correct Answer: Levigate powder with wetting agent, then disperse into structured vehicle

Q16. To reduce sedimentation without inducing flocculation, you should primarily:

• Increase vehicle viscosity with an appropriate polymer
• Add a flocculating electrolyte
• Raise temperature to reduce viscosity
• Use large, irregular crystals

Correct Answer: Increase vehicle viscosity with an appropriate polymer

Q17. During preformulation, adjusting pH away from the drug’s isoelectric point helps because it:

• Reduces solubility and increases caking
• Increases surface charge and electrostatic repulsion
• Eliminates the need for preservatives
• Guarantees zero sedimentation

Correct Answer: Increases surface charge and electrostatic repulsion

Q18. Which statement is TRUE regarding preservatives in deflocculated suspensions with nonionic surfactants?

• Nonionic surfactants never affect preservative efficacy
• Preservatives may partition into micelles, reducing free active concentration
• Electrolytes always enhance preservative action
• Preservatives eliminate the need for aseptic processing

Correct Answer: Preservatives may partition into micelles, reducing free active concentration

Q19. A practical way to reduce Ostwald ripening in suspensions is to:

• Broaden particle size distribution
• Minimize temperature cycling and use polymers that adsorb on particle surfaces
• Increase solubility of the drug substantially
• Use high electrolyte concentrations

Correct Answer: Minimize temperature cycling and use polymers that adsorb on particle surfaces

Q20. Which test best accelerates detection of caking tendency in deflocculated suspensions during development?

• Short-term color observation
• Centrifugation followed by redispersibility assessment
• Odor evaluation
• pH measurement only

Correct Answer: Centrifugation followed by redispersibility assessment

Q21. The most suitable rheology modifier to achieve pseudoplastic flow without high ionic sensitivity is generally:

• Sodium alginate at high salt levels
• Xanthan gum
• Gelatin near its isoelectric point
• Polyethylene glycol 400

Correct Answer: Xanthan gum

Q22. In deflocculated suspensions, “caking” refers to:

• Reversible sediment that easily redistributes on shaking
• Irreversible, compact sediment difficult to redisperse
• Foam formation during mixing
• Uniform dispersion of particles

Correct Answer: Irreversible, compact sediment difficult to redisperse

Q23. To lower the density difference (Δρ) and reduce sedimentation rate without flocculation, a formulator may:

• Add a water-miscible cosolvent like glycerol or sorbitol to the vehicle
• Increase particle density using heavy metal salts
• Use volatile organic solvents in final product
• Replace water with oil

Correct Answer: Add a water-miscible cosolvent like glycerol or sorbitol to the vehicle

Q24. Which is the most relevant measure of physical stability for a deflocculated suspension at rest?

• pKa of the drug
• Sedimentation volume and rate, plus redispersibility
• Melting point of the drug
• Specific rotation

Correct Answer: Sedimentation volume and rate, plus redispersibility

Q25. During preparation, levigation aids like glycerin are used primarily to:

• Increase electrostatic attraction
• Displace air and improve wetting before dispersion
• Induce controlled flocculation
• Act as primary preservatives

Correct Answer: Displace air and improve wetting before dispersion

Q26. Compared with flocculated systems, deflocculated suspensions generally show:

• Faster sedimentation and better redispersibility
• Slower sedimentation but higher risk of hard cake
• No sedimentation at all
• Permanent stability without shaking

Correct Answer: Slower sedimentation but higher risk of hard cake

Q27. For a poorly wettable, hydrophobic API, a suitable wetting agent in an oral aqueous deflocculated suspension is:

• Polysorbate 80
• Liquid paraffin
• Aluminum chloride
• Isopropyl ether

Correct Answer: Polysorbate 80

Q28. To avoid compressing the electrical double layer and maintain deflocculation, formulators should:

• Use minimal necessary electrolyte concentrations
• Use high concentrations of divalent cations
• Set pH at the isoelectric point
• Use strong cationic surfactants liberally

Correct Answer: Use minimal necessary electrolyte concentrations

Q29. A practical in-use instruction that supports dose uniformity for deflocculated suspensions is:

• Do not shake before use
• Shake well to redisperse before each dose
• Store in a freezer
• Add water to the bottle before each dose

Correct Answer: Shake well to redisperse before each dose

Q30. When selecting a suspending polymer for a deflocculated suspension, an important consideration is:

• High sensitivity to salts to promote flocculation
• Compatibility at product pH and desired pseudoplastic flow
• Insolubility in water
• High elasticity that prevents pouring

Correct Answer: Compatibility at product pH and desired pseudoplastic flow

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