Physicochemical approaches for SR/CR formulation MCQs With Answer

Physicochemical approaches for SR/CR formulation MCQs With Answer help M. Pharm students connect core physical chemistry with the design of sustained/controlled release systems. This quiz drills concepts such as diffusion and erosion mechanisms, polymer science (viscosity grade, permeability, glass transition), drug–polymer interactions, and the impact of solubility, pKa, particle size, and complexation on release kinetics. You’ll also test your understanding of modeling (Higuchi, Korsmeyer–Peppas, Hixson–Crowell), structural attributes (porosity, tortuosity, coating thickness), and formulation levers (salts, resins, plasticizers, surfactants, buffers). Each question is crafted to be application-focused and exam-ready, so you can diagnose how physicochemical properties are tuned to achieve robust, predictable SR/CR performance.

Q1. In a diffusion-controlled reservoir (membrane) system, the primary determinant of drug release rate is:

• Membrane permeability and thickness
• Drug’s biological half-life
• Tablet hardness alone
• Gastric emptying rate

Correct Answer: Membrane permeability and thickness

Q2. A key Higuchi model assumption for a drug dispersed in an insoluble matrix is:

• Drug concentration in the matrix is much higher than its solubility
• Matrix undergoes rapid surface erosion
• Drug diffusion is non-Fickian by default
• Membrane-controlled zero-order release is guaranteed

Correct Answer: Drug concentration in the matrix is much higher than its solubility

Q3. Drug release from hydrophilic matrix tablets (e.g., HPMC-based) is predominantly governed by:

• Diffusion through a hydrated gel layer coupled with matrix erosion
• Purely zero-order kinetics independent of gel properties
• Convective transport driven by GI peristalsis alone
• Enzymatic cleavage of polymer backbones only

Correct Answer: Diffusion through a hydrated gel layer coupled with matrix erosion

Q4. Increasing the viscosity grade of HPMC (e.g., from K4M to K100M) in a hydrophilic matrix typically:

• Slows release by forming a stronger, thicker gel with lower diffusivity
• Has no effect on release kinetics
• Accelerates release by enhancing water penetration
• Prevents gel formation, causing dose dumping

Correct Answer: Slows release by forming a stronger, thicker gel with lower diffusivity

Q5. Among acrylic polymers used for SR coatings, the one with higher permeability due to greater quaternary ammonium content is:

• Eudragit RS
• Eudragit RL
• Eudragit L100
• Eudragit S100

Correct Answer: Eudragit RL

Q6. For a weakly basic drug formulated in a hydrophilic matrix, incorporation of acidic excipients (lowering microenvironmental pH) will most likely:

• Increase drug solubility in the gel and speed up release
• Decrease drug solubility and slow release
• Have no effect on release
• Cause surface erosion to dominate

Correct Answer: Increase drug solubility in the gel and speed up release

Q7. Reducing drug particle size in an insoluble polymer matrix (e.g., ethylcellulose) typically:

• Decreases surface area and slows initial release
• Increases surface area and can increase burst release
• Eliminates diffusion as a mechanism
• Converts release to zero-order

Correct Answer: Increases surface area and can increase burst release

Q8. In the Korsmeyer–Peppas model for cylindrical matrices, an exponent (n) in the range 0.45 < n < 0.89 indicates:

• Fickian diffusion
• Case-II transport (zero-order swelling-controlled)
• Anomalous (non-Fickian) transport
• Pure erosion control

Correct Answer: Anomalous (non-Fickian) transport

Q9. For ion-exchange resinate-based SR systems, the dominant external factor modulating drug release is:

• Counter-ion concentration (e.g., Na+/Cl−) in the dissolution medium
• Ambient light intensity
• Tablet colorant concentration
• Capsule shell thickness

Correct Answer: Counter-ion concentration (e.g., Na+/Cl−) in the dissolution medium

Q10. A reservoir system approaches zero-order release when:

• Membrane area and thickness are constant and the core maintains constant drug activity (excess undissolved drug)
• The membrane swells substantially over time
• Drug is fully dissolved with rapidly depleting core activity
• Coating is intentionally heterogeneous

Correct Answer: Membrane area and thickness are constant and the core maintains constant drug activity (excess undissolved drug)

Q11. In porous matrices, the effective diffusivity (De) is most favorably altered to increase release by:

• Decreasing porosity and increasing tortuosity
• Increasing porosity and decreasing tortuosity
• Decreasing both porosity and tortuosity
• Increasing tortuosity only

Correct Answer: Increasing porosity and decreasing tortuosity

Q12. Increasing plasticizer content (e.g., triethyl citrate) in an ethylcellulose film coating most commonly:

• Decreases film permeability and slows release
• Increases film permeability by enhancing chain mobility, often speeding release
• Eliminates the need for a polymer
• Prevents film formation entirely

Correct Answer: Increases film permeability by enhancing chain mobility, often speeding release

Q13. A physicochemical strategy to slow the release of a weakly basic, highly soluble drug is to:

• Form a hydrophobic salt (e.g., pamoate or stearate)
• Micronize the drug to increase surface area
• Add strong surfactants to increase wetting
• Use an enteric polymer that dissolves in the stomach

Correct Answer: Form a hydrophobic salt (e.g., pamoate or stearate)

Q14. Which polymer is best known for predominantly surface erosion, enabling near zero-order release in erosion-controlled systems?

• PLGA (poly(lactide-co-glycolide))
• Polyanhydrides
• PVA (polyvinyl alcohol)
• PEO (polyethylene oxide)

Correct Answer: Polyanhydrides

Q15. A prerequisite for osmotic pump formulations to sustain release is that the core contains:

• Only poorly soluble drug without any osmogen
• Components that generate sufficient osmotic pressure (highly soluble drug or added osmogen)
• Hydrophobic waxes exclusively
• Enzymes to cleave the coating

Correct Answer: Components that generate sufficient osmotic pressure (highly soluble drug or added osmogen)

Q16. A practical method to minimize burst release from a hydrophilic matrix is to:

• Increase drug surface enrichment during compression
• Granulate or coat drug particles with polymer to reduce surface localization
• Reduce polymer content drastically
• Polish tablets with hydrophilic surfactants only

Correct Answer: Granulate or coat drug particles with polymer to reduce surface localization

Q17. Selecting a film-forming polymer with a glass transition temperature (Tg) close to storage temperature generally leads to:

• Increased chain mobility and higher water permeability of the film
• Lower permeability due to rigidification
• No impact on transport properties
• Instant crystallization of the drug

Correct Answer: Increased chain mobility and higher water permeability of the film

Q18. In hydrophilic matrix tablets, high levels of magnesium stearate typically:

• Increase wettability and speed up release
• Decrease wettability and can slow initial release
• Have no effect on release variability
• Convert diffusion control to pure erosion control

Correct Answer: Decrease wettability and can slow initial release

Q19. For a highly soluble drug embedded in an insoluble matrix (e.g., ethylcellulose), increasing drug loading generally:

• Reduces pore formation and slows release
• Increases channel formation upon dissolution and speeds release
• Eliminates the need for plasticizer
• Ensures zero-order release automatically

Correct Answer: Increases channel formation upon dissolution and speeds release

Q20. The Hixson–Crowell cube-root model is most appropriate for dosage forms where:

• Diffusion through a constant geometry dominates without dimensional change
• Surface area and diameter decrease over time due to erosion/dissolution while shape remains geometrically similar
• Pure osmotic pumping controls release
• Enzymatic degradation is the only mechanism

Correct Answer: Surface area and diameter decrease over time due to erosion/dissolution while shape remains geometrically similar

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